DO THE TON

Blood Sweat Tears and Grease => Projects => Specials => Topic started by: themotoworks on May 25, 2018, 20:10:19

Title: GT380 ground up build
Post by: themotoworks on May 25, 2018, 20:10:19
Starting a new project with a new idea, I picked up a gt380 for free with a valid registration and want to use it as a design experiment to see if I can put some ideas I've had into one single project.  The idea is really to conceive the entire bike before really building anything, my hope is that it both makes a really functional bike, speeds up the mechanical side of the build process, and makes for a really nice looking build.  I pulled the motor already and have been measuring it to put it into solidworks and integrate it with the other parts.  The front end is a gsxr-750 with custom made triples and a custom machined spoked hub, rear end is all custom fab, going to run an ohlins shock for a 900ss ducati because I'm familiar with them, planning on a large diameter tube backbone frame and machined aluminum swingarm mounts that combine the engine mount, frame to engine mounting and subframe/seat mount... came up with some sketches, and talked to jeremy lacy about him basically designing the bodywork and look of the bike, should be interesting. 

(http://i1266.photobucket.com/albums/jj540/smp4616/Mobile%20Uploads/IMG_20180525_153012159_zps3spjhcee.jpg)
(http://i1266.photobucket.com/albums/jj540/smp4616/Mobile%20Uploads/IMG_20180524_155600_238_zpswerp6och.jpg)
(http://i1266.photobucket.com/albums/jj540/smp4616/gt380_zpsilzwcsty.jpg)
Title: Re: GT380 ground up build
Post by: farmer92 on May 25, 2018, 20:44:32
This looks like a sweet project!
Just wondering how you ended up with the frame style you chose.
I presume by large diameter backbone you mean something like an Egli frame,
(https://uploads.tapatalk-cdn.com/20180525/c9100c0c0664e870fb60c275ff3ac88c.jpg)
That one is for a tz350 i believe.
What did you plan for material?
Title: Re: GT380 ground up build
Post by: themotoworks on May 25, 2018, 21:05:02
chromoly, I'm having trouble finding large diameter thin wall tubing in that material though, I may need to have a sheet rolled. 
Title: Re: GT380 ground up build
Post by: farmer92 on May 25, 2018, 21:18:03
Figured it would be chromo, was hoping maybe you would have had better luck than me at finding something in a proper size.

Did you model it yet? What sort of weight are you aiming for for the frame?

I modelled several frame designs this design seemed to give the best stiffness to weight ratio, it was about 18lbs
Title: Re: GT380 ground up build
Post by: irk miller on May 25, 2018, 22:44:03
YZ frames were pretty light.  When the shock tubed into the frame, the backbone was stamped.

(http://pulpmx.com/app/uploads/2017/09/csteel124_3.png)

They later went to this in 80.   

(http://farm7.static.flickr.com/6185/6082133407_47f94a75dc.jpg)

Title: Re: GT380 ground up build
Post by: teazer on May 26, 2018, 00:34:01
How large do you want the backbone?

http://www.onlinemetals.com/merchant.cfm?pid=10434&step=4&showunits=inches&id=250&top_cat=197

That's 3.0'' but it's pretty thick.  You may have to go to rolling a sheet into tube as you suggested.

in DOM you can get up to 4.0"    http://www.onlinemetals.com/merchant.cfm?pid=12690&step=4&showunits=inches&id=283&top_cat=197


Title: Re: GT380 ground up build
Post by: themotoworks on May 26, 2018, 08:45:37
I talked to Fritz Egli and he actually told me what I had suspected for a while, he doesn't use chromoly tubing, the modulus of all steel is basically the same, and there's not going to be a difference in the stiffness from a513 to 4130 unless it's being bent to yield, which it shouldn't be.  4" .083" is available, I'll model a frame from that and see how well it does, from my experience, changing the diameter or wall thickness of the main backbone section very predictably changes the tortional stiffness of the front end
Title: Re: GT380 ground up build
Post by: Hurco550 on May 26, 2018, 12:03:32
A friend of mine is working on building a tube chassis autocross truck, and we've been researching the use of docol r8 tubing vs chromoly. Similar weight, yet there are far less brittleness issues in the heat affected zone from welding. It just became available in the u.s. market fairly recently, though it's been used in Europe for a bit. Just another possible option. When i build a frame (someday) ill likely use it.


http://www.aedmotorsport.com/catalog/product/docol-tube-r8

Sent from my SM-G920V using Tapatalk

Title: Re: GT380 ground up build
Post by: farmer92 on May 26, 2018, 12:29:17
Donít they all weigh nearly the same? Like less than 1% density difference?

I was under the impression that you have more elastic deformation from 1020 vs 4130
But that they both reach plastic deformation at nearly the same points.
Title: Re: GT380 ground up build
Post by: themotoworks on May 26, 2018, 12:51:11
yeah, the density of all steel is basically the same, the modulus is basically the same, the things that vary with different alloys and heat treatments are the tensile strength and the yield, which really only determines where they "break".  so if I were designing a roll cage, chromoly would be a good choice, because for a given weight roll cage, the chromoly one would take more of a beating before it gave way, but in a design built to be predictable under known loading, with an adequate safety factor in the design, there wouldn't be a difference in performance between 4130 and a513
Title: Re: GT380 ground up build
Post by: themotoworks on May 27, 2018, 12:48:21
(http://i1266.photobucket.com/albums/jj540/smp4616/gt3801_zpsp9dirbzd.jpg)
trying to finish designing the swingarm and rear frame mount, which is a big p.i.t.a. because the rear engine mounts are kicked way off to the right of the engine centerline, not ideal but I can make it work
Title: Re: GT380 ground up build
Post by: themotoworks on May 31, 2018, 18:09:46
(http://i1266.photobucket.com/albums/jj540/smp4616/gt380%20timing_zpslz5ozhte.png)

I'm planning on slightly modifying the engine, cutting the piston skirt and adding piston ports as well as reed valves and tuned pipes, anyone on here know much about 2 strokes?  Will this timing be alright?  It's a bit modified on the intake side to allow for the reed valve to stop reversion back into the carbs instead of the piston blocking the back flow. 

also made a lot of progress on designing the rear suspension, need to finalize the shock choice so I can finish designing all the linkages etc.
Title: Re: GT380 ground up build
Post by: teazer on May 31, 2018, 18:51:36
Where did those data points come from? Is that what you measured stock timing as or where you want it to be?  For a free revving motor, those numbers are not close to where you want them to be.  IMHO. try EO at 90 ATDC, TO at 120 ATDC and Intake at say 1110 BTDS as a starting point and work out the time area at target peak revs and see how wide you would have to go to reach the sort of BMEP levels you want at target RPMs. 

Of course you will also need to design a pipe to work with the target port shapes - assuming there's enough metal to port it to those numbers. Look at what Barton motors did with the water cooled Sparton 500 which was based on that bottom end. 

Suitable sized reed boxes are a good way to add additional intake time area but that may cause clearance issues with the rear cylinder base studs.

Just as a point of reference with a more modern motor, an RS250 Aprilia lightly cleaned up makes over 60hp from 250cc, so a triple based on the same ports could theoretically make around 90hp.  Your motor will not have exhaust power valves or the port area, or crankcase reed area of an RS250 so that gives you a base to consider.  By comparison, a full race GT250 or T20 makes closer to 40hp with a TZ crank, later style multi port barrels etc .

You may want to look at what anyone with a T20/GT250 or even a T315/350 does to make power and start there. I recall riding a beautiful T350 with 6mm spacers under the cylinders many years ago. It looked totally stock and went remarkably fast.

How much HP at what Revs is your target?

Last time I looked at one of those, I ended up with EO at 80 ATDC, and transfers at 110 ATDC peaking at almost 10,000 with restricted intakes to keep revs down and some semblance of bottom end (ie below 6k).   
Title: Re: GT380 ground up build
Post by: themotoworks on May 31, 2018, 21:37:38
those exhaust and transfer numbers were based on measuring the stock engine, the intake to crank timing is based on adding windows into the piston skirt and cutting the base of the skirt back, which gave longer duration, requiring a reed valve, but possibly making more power.  I downloaded some long book on 2 stroke performance, looked like it was from the 70's, but it has a lot of info on port size based on rpm etc., I want to make this thing peppy but not go so overboard that I lose months to engine tweaking.  The idea for this build was to really test the idea of building a bike completely in the computer, then machining and welding to the prints, then assembling, and seeing if it would work, or what would need to be changed to make it work.  I hesitate to go neck deep into the engine, but at the same time I don't want to leave it as sleepy as stock, especially when the rest of the bike is really build for performance.  also since my slow time at work is usually the summer months, if this goes past september, it may not see the light of day until next summer

Here's where I'm at with the rear suspension so far, plots look good for the geometry, clearances look pretty good in SW, just need to flesh out things like the linkage and swingarm, I'm also a little hesitant to finalize the design without having the shock in hand, and since ohlins doesn't give out cad info or drawings, that might force a bit of a wait...


(http://i1266.photobucket.com/albums/jj540/smp4616/gt380suspension_zpsqchgnuew.png)
(http://i1266.photobucket.com/albums/jj540/smp4616/gt380%20suspension%20plots_zps3itofdk8.png)
Title: Re: GT380 ground up build
Post by: irk miller on May 31, 2018, 22:03:03
What's your wheelbase?
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 01, 2018, 07:10:30
I'm aiming for 54.5" at static sag
Title: Re: GT380 ground up build
Post by: teazer on Jun 01, 2018, 08:09:24
I dug out a previous simulation run for a more or less stock 380 and changed inlet timing to yours and lost power everywhere.  The ports are way too large and lose intake velocity and therefore crankcase filling. Raise the exhaust 2.5-3.0mm, transfers by 2mm and drop the intakes 2mm to start.  Check those numbers with your engine builder.  There are infinite number of combinations and a few of them work better than others.  You will have to machine teh head to get compression back  too.
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 01, 2018, 08:22:08
the stock intake is 69 degrees, what simulator are you using?
Title: Re: GT380 ground up build
Post by: teazer on Jun 02, 2018, 01:45:19
283 ATDC or 77 BTDC modeled in Mota 6.1 or -x beta version.  283* is 24.2mm BTDC and your 123* works out to 44.1mm BTDC (plus piston length of course). 

MOTA ignores actual intake port dimension when using reeds because it assumes that the reeds will effectively modulate flow but with excessively large ports, it loses flow velocity even with reeds. The sections of the reeds and port must be matched to work effectively.

BTW, you still get harmonics in the intakes with reeds and reversion - just not quite as bad. 
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 02, 2018, 20:13:44
(http://i1266.photobucket.com/albums/jj540/smp4616/Mobile%20Uploads/IMG_20180602_102202153_HDR_zps25rvla8v.jpg)
(http://i1266.photobucket.com/albums/jj540/smp4616/Mobile%20Uploads/IMG_20180602_180857_587_zpsqa3wvezy.jpg)

finished up the rear hub, it's modeled in the solidworks bike so it's nice to know already that things will fit, next going to try to finish the front hub sunday before I need to do actual work at the shop haha

Title: Re: GT380 ground up build
Post by: CrabsAndCylinders on Jun 03, 2018, 01:15:51
That is pure motorcycle porn, love it!
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 12, 2018, 18:38:57
how much dead air can be between the piston port and the reed valve?  I'm trying to design a weld in transition to hold the reed valve, but I can't get it all that close to the cylinder without having issues clearing the cylinder nuts... can there be some volume there or is any volume a dealbreaker?
Title: Re: GT380 ground up build
Post by: farmer92 on Jun 12, 2018, 20:02:11
how much dead air can be between the piston port and the reed valve?  I'm trying to design a weld in transition to hold the reed valve, but I can't get it all that close to the cylinder without having issues clearing the cylinder nuts... can there be some volume there or is any volume a dealbreaker?


Why are you using piston porch and reeds at the same time?

Poke a few holes through the Pistons and stuff something in the crankcase to take up space to make up for the added volume.
Title: GT380 ground up build
Post by: farmer92 on Jun 12, 2018, 20:18:26
The more volume between the piston port and reed valve, The longer the delay between piston port opening and read valve opening.

Letís take a look at the limit cases,

 Very Low RPM:
The piston port will open and cause a vacuum air will flow from the dead space into the crankcase eventually the read valve will open ended the pressure will stabilize in both spaces and do the piston port will close.

Very high rpm:
The piston port will open which will cause a vacuum and the air will be drawn from the dead space into the crank case the piston port will begin to close as air starts to flow past the read valve.
The piston port will be closed and the air will slam into the piston and revert back closing the reader valve keeping the dead space under positive pressure.

somewhere in the middle you have different resonance frequencies and overtones going on.

The gist of it is that it will make certain rpmís much better than others depending on that volume and the effects of that volume will be reduced as you manage to shrink it.

It will more than likely make it more difficult to tune as well.

Edit: I seem to have missed understood you after re-reading a few posts back.
When you said the piston ports I thought you meant a piston ported engine as well as reads and not that you were going to cut a window into the intake side of the piston skirt, my bad...

With that being said yes that volume is extremely important to the characteristics of your engine.
If you make it to large the motion of the piston will have a harder time creating enough vacuum to open up the reeds.
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 26, 2018, 20:02:32
looking for some input on where to go from here, I carefully measured everything and I mean everything... in the gt380, predicted HP runs about 30, which based on the claimed 40 seems about right for 70's japanese marketing.  now where should I look for improvements?  here's the data from the MOTA program, based on my measurements which should be pretty spot on for that engine.  I was thinking about adding a reed to the simulation but I feel like I should start with timing and port size first...

     

 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
      *                                                                     *
      *                       ENGINE PERFORMANCE FILE                       *
      *                                                                     *
      *  FILE NAME: C:\USERS\PUBLIC\MOTA\SAMPLES-6\GT380TUNED.PER           *
      *                                                                     *
      *  DATE (D/M/Y): 26/6/2018                                            *
      *                                                                     *
      *  TIME: 4:58 p.m.                                                    *
      *                                                                     *
      *  COMMENT: "Optimisation output file"                                *
      *                                                                     *
      * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *



      ENGINE SPECIFICATION
      --------------------
 
      BASIC ENGINE CONFIGURATION:
        Piston controlled induction.
        Single piece expansion chamber.
 
 
      PIPE STEP FACTOR:
      Lower Limit:  4.1   Upper Limit: 13.0   Value: 10.0
 
 
      SCAVENGING PARAMETERS:
 
        Maximum Short Circuit Ratio: 0.20
        Maximum Displacement Scavenging Fraction: 0.80
        Scavenge Ratio for Zero Short Circuit: 1.00
        Scavenge Ratio for No Displacement Scavenging: 0.50



       BORE      STROKE     CONNECTING ROD   GUDGEON PIN
       (mm)       (mm)        LENGTH (mm)    OFFSET (mm)
 
      54.00      54.00          110.00           0.00



      BORE/STROKE   CONNECTING ROD LENGTH
         RATIO          /STROKE RATIO
 
        1.0000             2.0370



      BOX NAME                  CLEARANCE       SWEPT       COMPRESSION
                               VOLUME (cc)   VOLUME (cc)       RATIO
 
      CRANKCASE                  225.00        123.67           1.55
      CYLINDER                    10.00        123.67           8.59



      CALORIFIC VALUE OF    AIR FUEL   THROTTLE AREA
         FUEL (BTU/lb)        RATIO        RATIO
 
           18536.3            13.00        1.000



      COMBUSTION PARAMETERS:
 
      COMBUSTION      BURN PERIOD
      EFFICIENCY       (degrees)
 
         0.800            55.0



      IGNITION TIMING:
 
      IGNITION TIMING
       (degrees BTDC)
          20.0



      AMBIENT CONDITIONS:
 
      TEMPERATURE (F)   PRESSURE (psi)
 
            68.0            14.70



      PISTON PORT DIMENSIONS:
 
      PORT     NUMBER  BRIDGED     MAXIMUM PORT WIDTH    HEIGHT  CORNER RADII
      NAME    OF PORTS  (Y/N)   ANGULAR   ARC    CHORD    (mm)    TOP  BOTTOM
                                 (deg)    (mm)    (mm)            (mm)  (mm)
 
      INLET       2       Y      38.20   18.00   17.67    19.04   3.00   3.00
      TRANSFER    2       N      65.78   31.00   29.33    10.99   3.00   6.00
      EXHAUST     1       -      78.52   37.00   34.17    20.85   5.00   5.00
 
 
      PORT           BRIDGE     RADII AT BRIDGE
      NAME            WIDTH       TOP   BOTTOM
                      (mm)       (mm)    (mm)
 
      INLET           5.00       3.00    3.00
 
 
      PORT            TOTAL      ATTITUDE ANGLES
      NAME             AREA      AXIAL    RADIAL
                     (sq.cm)     (deg)     (deg)
 
      INLET           6.5732       5.0      0.0
      TRANSFER        6.0571       0.0     20.0
      EXHAUST         6.9103      15.0      0.0
 
 
      PISTON PORT TIMINGS:
 
      PORT NAME     START OPEN   FULL OPEN   START OPEN    FULL OPEN
                    (deg ATDC)  (deg ATDC) (mm from TDC) (mm from TDC)
 
      INLET           292.0        348.0        19.77         0.73
      TRANSFER        120.0        180.0        43.01        54.00
      EXHAUST          96.0        180.0        33.15        54.00



      INLET DUCT
 
        A bellmouth is present at the inlet of section 1.
        Section 4 is the inlet duct portion inside the barrel.
 
      SECTION  LENGTH  DIAMETER IN  DIAMETER OUT   AREA IN  AREA OUT
                (mm)      ( mm)         (mm)       (sq.cm)   (sq.cm)



         1      13.5      25.0         29.0          4.91      6.61
         2      95.0      41.0         25.0         13.20      4.91
         3      25.0      70.0         41.0         38.48     13.20
         4      56.0      29.0         28.9          6.61      6.55
 
 
      TRANSFER DUCTS
 
        Smooth entry to each transfer duct 2 is NOT assumed.
        Diameters and areas are those of each individual duct in a group.
 
 
      TRANSFER    (2 separate ducts)
 
      SECTION  LENGTH  DIAMETER IN   DIAMETER OUT   AREA IN  AREA OUT
                (mm)       (mm)         (mm)        (sq.cm)   (sq.cm)
 
         1      50.0      24.0         19.0          4.52      2.85
 
 
 
      EXHAUST DUCT (single air cooled system)
 
      SECTION    LENGTH      DIAMETER          AREA          CONE     VOLUME
                  (mm)      IN     OUT      IN      OUT      ANGLE     (cc)
                           (mm)   (mm)    (sq.cm) (sq.cm)    (deg)
 
       BARREL     60.0     29.2   35.0      6.67    9.62
         1       282.0     32.6   43.7      8.35   15.00      2.3      324.6
         2       227.6     43.7  112.7     15.00   99.76     17.2     1164.1
         3       202.9    112.7  106.0     99.76   88.25      1.9     1906.1
         4        75.3    106.0   31.8     88.25    7.94     52.5      307.9
        TAIL     110.7     29.2   29.2      6.70    6.70
 
 
      ENGINE PERFORMANCE INDICATORS
      -----------------------------
 
      SPEED     POWER    TORQUE       POWER    TORQUE
      (rpm)      (kW)     (Nm)         (hp)   (ft lbf)
 
       1000     0.806     7.698       1.081     5.678
       2000     1.865     8.905       2.501     6.568
       3000     2.626     8.359       3.521     6.165
       4000     3.188     7.610       4.275     5.613
       5000     4.078     7.789       5.469     5.745
       6000     4.470     7.115       5.995     5.247
       7000     6.521     8.896       8.745     6.561
       8000     7.284     8.695       9.769     6.413
       9000     6.165     6.542       8.268     4.825
      10000     6.038     5.766       8.098     4.253
 
      SPEED      IGNITION TIMING       AIR FUEL
      (rpm)       (degrees BTDC)         RATIO
 
       1000            20.0              13.00
       2000            20.0              13.00
       3000            20.0              13.00
       4000            20.0              13.00
       5000            20.0              13.00
       6000            20.0              13.00
       7000            20.0              13.00
       8000            20.0              13.00
       9000            20.0              13.00
      10000            20.0              13.00
 
      SPEED     MEAN EFFECTIVE PRESSURES  (atm)
      (rpm)     BMEP     PMEP     FMEP     IMEP
 
       1000     3.860    0.233    0.029    4.122
       2000     4.465    0.339    0.059    4.862
       3000     4.191    0.326    0.088    4.605
       4000     3.816    0.282    0.117    4.215
       5000     3.905    0.280    0.147    4.332
       6000     3.567    0.247    0.176    3.990
       7000     4.460    0.353    0.205    5.019
       8000     4.360    0.322    0.234    4.916
       9000     3.280    0.276    0.264    3.820
      10000     2.891    0.223    0.293    3.408
 
      SPEED   FUEL CONSUMPTION        FLOW RATIOS           SCAVENGE  RATIOS
      (rpm)    (BSFC: lb/hph)     DELIVERY    EXHAUST       MASS      VOLUME
 
       1000         0.889         0.634438   0.634444       0.634      0.593
       2000         0.969         0.799808   0.800056       0.800      0.794
       3000         0.921         0.713604   0.713781       0.715      0.706
       4000         0.892         0.629147   0.629124       0.629      0.606
       5000         0.809         0.584214   0.585251       0.585      0.552
       6000         0.766         0.505223   0.506570       0.506      0.478
       7000         0.856         0.705791   0.705976       0.706      0.714
       8000         0.807         0.650044   0.650178       0.650      0.652
       9000         0.920         0.557644   0.558178       0.560      0.529
      10000         0.870         0.464691   0.464099       0.464      0.416
 
      SPEED              EFFICIENCIES             PERCENTAGE ENERGY LOSS
      (rpm)     SCAVENGE   TRAPPING   CHARGING      IN EXHAUST SYSTEM
 
       1000       0.721      0.628      0.399             21.01
       2000       0.762      0.568      0.454             25.18
       3000       0.738      0.598      0.427             20.99
       4000       0.710      0.620      0.390             16.43
       5000       0.693      0.692      0.405             20.99
       6000       0.659      0.733      0.371             18.78
       7000       0.727      0.648      0.458             14.42
       8000       0.707      0.685      0.445             12.97
       9000       0.666      0.606      0.339             12.40
      10000       0.635      0.652      0.303             14.21
 
                   PEAK CYLINDER         TEMPERATURE LIMITS AT CENTRE
      SPEED   PRESSURE    TEMPERATURE    OF THE EXPANSION CHAMBER (F)
      (rpm)     (atm)         (F)           MEAN      LOW      HIGH
 
       1000     37.96       2937.11        549.9    544.3     567.4
       2000     42.49       3109.53        500.3    483.2     523.4
       3000     39.84       3012.49        560.1    548.5     586.2
       4000     36.87       2941.83        608.8    592.0     642.8
       5000     39.57       2984.38        634.4    606.1     688.2
       6000     36.98       2890.37        682.6    658.5     727.0
       7000     42.41       3043.50        654.0    614.5     726.8
       8000     41.49       2989.56        690.9    651.5     738.6
       9000     31.44       2803.08        612.5    582.3     652.7
      10000     29.38       2793.88        653.3    621.0     697.3
 
      The Specific Time Area of a port is the sum of all port areas
      over time divided by the cylinder swept volume.
      The units sec/metre and sec.sq mm/cc are equivalent.
 
              SPECIFIC PORT TIME AREA
                (sec/metre x 10000)
      SPEED    INLET   TRANSFER   EXHAUST                                                                               
      (rpm)                                                                                                             
 
      1000     796.7     623.9     997.7
      2000     398.3     311.9     498.9
      3000     265.6     208.0     332.6
      4000     199.2     156.0     249.4
      5000     159.3     124.8     199.5
      6000     132.8     104.0     166.3
      7000     113.8      89.1     142.5
      8000      99.6      78.0     124.7
      9000      88.5      69.3     110.9
     10000      79.7      62.4      99.8
 
  Elapsed time: 38.00 seconds
Title: Re: GT380 ground up build
Post by: teazer on Jun 26, 2018, 21:33:19
That's a good start.

There are all sorts of giveaways in that file for example CR looks too high but check the BSFC which is high - indicating inefficiency and BMEP which is half of where it should be.  It is a very mild state of tune by modern standards. Your garden implements are probably mugh higher state of tune.

For a simple place to start, try EO at 90 ATDC and TO at 120 just to get the ball rolling. Then look at wider ports and longer intake duration and see where that takes you. For IO, try 280 or 285 degrees to start with and move from there and add GT550 28mm carbs with matching intake ports.  You could also simulate raising the inlet port roof to 360 degrees and then work out if that's feasible or if it leaves the rings exposed.

BTW, what pipes are those that you measured and are they OD dimensions or ID?

You may also want to remeasure the intake port dimensions.  What does the inlet velocity wave look like?
 
Title: Re: GT380 ground up build
Post by: teazer on Jun 26, 2018, 21:45:28
I entered your port dimensions and exhaust duct and left a simple 24mm carb and immediately got 57 theoretical HP.  Check teh intake duct and correct that and try wilder port timing to see the effect.
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 26, 2018, 21:53:56
I saw that I had my intake tract backwards, I wasn't sure how the numbers were arranged, I fixed it and got much better results (cool program, a bit lacking in explanations).  I'll continue to play, may not even need a reed valve

what's bsfc?
Title: Re: GT380 ground up build
Post by: teazer on Jun 26, 2018, 22:14:17
It's not perfect, but pretty amazing once you get the hang of it.  Only issue to watch for is that it allows you to enter crazy port widths because it has no idea how little metal there is to work with. 

Once you start to get more radical, the larger carbs start to pay off.  When you get closer, you can do a series of runs with timing changing by say 2 degrees at a time to see the effect.

If you have V10, you can choose a range of files to simulate at the same time.  That's cool but needs a fast PC. 38 seconds isn't bad.  Mine took 32 to do your run with 250rpm steps for more data points.  You can then re-run at a specific RPM to get the wave files at that RPM. That's useful for problem points in the curve or close to peak to see what's going on.

Have fun. 
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 27, 2018, 07:45:52
I tweaked it to peak 70hp at 9k, but it has some dips at 4 and 6 that I'd want to avoid.  a wera instructor with a 200hp h2 around here was telling me I should install case reeds... I think he had a few beers, but it might be cool if not too much work
Title: Re: GT380 ground up build
Post by: farmer92 on Jun 27, 2018, 07:59:57
https://youtu.be/whb86fnEjdI
200cc inline 4 2t made from 4x50cc scooter engines, stuffed into a ysr50 frame.

https://youtu.be/C_A6A53YMHI
Honda 800 v8
Made from 2 400f engines.


Anything is possible hahaha
Title: Re: GT380 ground up build
Post by: irk miller on Jun 27, 2018, 08:19:54
Honda 800 v8
Made from 2 400f engines.


Anything is possible hahaha

I'll take your Honda 800 and raise you a supercharged 1500 made from CB750 motors...

https://www.youtube.com/watch?v=hUXz68etBIc

23tbucket was building this over on Hondachopper.  Unfortunately, he passed away this June right when the trike was ready for reassembly.

https://www.tapatalk.com/groups/hondachopper/reverse-trike-with-supercharged-1500cc-engine-t57239.html
Title: Re: GT380 ground up build
Post by: farmer92 on Jun 27, 2018, 09:08:20
I'll take your Honda 800 and raise you a supercharged 1500 made from CB750 motors...

https://www.youtube.com/watch?v=hUXz68etBIc

23tbucket was building this over on Hondachopper.  Unfortunately, he passed away this June right when the trike was ready for reassembly.

https://www.tapatalk.com/groups/hondachopper/reverse-trike-with-supercharged-1500cc-engine-t57239.html

Thatís nuts!
The amount of time that must have gone into the conception of it must be staggering
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 27, 2018, 11:42:08
I remembered what the point of this build was and stopped playing too much, I optimized some pipes and found cutting the piston skirt 10mm seems to bump power and not have much in the way of flat spots, the intake tract is designed around some carbs I had saved for this bike, power shows 60 with a pretty smooth curve, I can live with that, the whole idea of this project was to learn about the process of designing a bike wholly, manufacturing the parts, and then assembling as efficiently as possible, going full radical on the engine isn't in the cards for this one, but it will be cool to keep playing with 2 strokes, I think I could build some stupid stuff with them. 





      * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
      *                                                                     *
      *                       ENGINE PERFORMANCE FILE                       *
      *                                                                     *
      *  FILE NAME: C:\USERS\PUBLIC\MOTA\SAMPLES-6\GT1D.PER                 *
      *                                                                     *
      *  DATE (D/M/Y): 27/6/2018                                            *
      *                                                                     *
      *  TIME: 10:33 a.m.                                                   *
      *                                                                     *
      *  COMMENT: "Optimisation output file"                                *
      *                                                                     *
      * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *



      ENGINE SPECIFICATION
      --------------------
 
      BASIC ENGINE CONFIGURATION:
        Piston controlled induction.
        Single piece expansion chamber.
 
 
      PIPE STEP FACTOR:
      Lower Limit:  4.1   Upper Limit: 16.0   Value: 10.0
 
 
      SCAVENGING PARAMETERS:
 
        Maximum Short Circuit Ratio: 0.20
        Maximum Displacement Scavenging Fraction: 0.80
        Scavenge Ratio for Zero Short Circuit: 1.00
        Scavenge Ratio for No Displacement Scavenging: 0.50



       BORE      STROKE     CONNECTING ROD   GUDGEON PIN
       (mm)       (mm)        LENGTH (mm)    OFFSET (mm)
 
      54.00      54.00          110.00           0.00



      BORE/STROKE   CONNECTING ROD LENGTH
         RATIO          /STROKE RATIO
 
        1.0000             2.0370



      BOX NAME                  CLEARANCE       SWEPT       COMPRESSION
                               VOLUME (cc)   VOLUME (cc)       RATIO
 
      CRANKCASE                  225.00        123.67           1.55
      CYLINDER                    10.00        123.67           8.49



      CALORIFIC VALUE OF    AIR FUEL   THROTTLE AREA
         FUEL (BTU/lb)        RATIO        RATIO
 
           18536.3            13.00        1.000



      COMBUSTION PARAMETERS:
 
      COMBUSTION      BURN PERIOD
      EFFICIENCY       (degrees)
 
         0.800            55.0



      IGNITION TIMING:
 
      IGNITION TIMING
       (degrees BTDC)
          24.5



      AMBIENT CONDITIONS:
 
      TEMPERATURE (F)   PRESSURE (psi)
 
            68.0            14.70



      PISTON PORT DIMENSIONS:
 
      PORT     NUMBER  BRIDGED     MAXIMUM PORT WIDTH    HEIGHT  CORNER RADII
      NAME    OF PORTS  (Y/N)   ANGULAR   ARC    CHORD    (mm)    TOP  BOTTOM
                                 (deg)    (mm)    (mm)            (mm)  (mm)
 
      INLET       2       Y      38.20   18.00   17.67    19.17   3.00   3.00
      TRANSFER    2       N      65.78   31.00   29.33    10.99   3.00   6.00
      EXHAUST     1       -      78.52   37.00   34.17    21.31   5.00   5.00
 
 
      PORT           BRIDGE     RADII AT BRIDGE
      NAME            WIDTH       TOP   BOTTOM
                      (mm)       (mm)    (mm)
 
      INLET           5.00       3.00    3.00
 
 
      PORT            TOTAL      ATTITUDE ANGLES
      NAME             AREA      AXIAL    RADIAL
                     (sq.cm)     (deg)     (deg)
 
      INLET           6.6213       5.0      0.0
      TRANSFER        6.0571       0.0     20.0
      EXHAUST         7.0667      15.0      0.0
 
 
      PISTON PORT TIMINGS:
 
      PORT NAME     START OPEN   FULL OPEN   START OPEN    FULL OPEN
                    (deg ATDC)  (deg ATDC) (mm from TDC) (mm from TDC)
 
      INLET           270.0        311.0        30.37        11.19
      TRANSFER        120.0        180.0        43.01        54.00
      EXHAUST          95.0        180.0        32.69        54.00



      INLET DUCT
 
        A bellmouth is present at the inlet of section 1.
        Section 4 is the inlet duct portion inside the barrel.
 
      SECTION  LENGTH  DIAMETER IN  DIAMETER OUT   AREA IN  AREA OUT
                (mm)      ( mm)         (mm)       (sq.cm)   (sq.cm)



         1      75.0      60.0         35.0         28.27      9.62
         2      95.0      35.0         29.0          9.62      6.61
         3      25.0      29.0         29.0          6.61      6.61
         4      56.0      29.0         29.0          6.61      6.60
 
 
      TRANSFER DUCTS
 
        Smooth entry to each transfer duct 2 is NOT assumed.
        Diameters and areas are those of each individual duct in a group.
 
 
      TRANSFER    (2 separate ducts)
 
      SECTION  LENGTH  DIAMETER IN   DIAMETER OUT   AREA IN  AREA OUT
                (mm)       (mm)         (mm)        (sq.cm)   (sq.cm)
 
         1      50.0      24.0         19.0          4.52      2.85
 
 
 
      EXHAUST DUCT (single air cooled system)
 
      SECTION    LENGTH      DIAMETER          AREA          CONE     VOLUME
                  (mm)      IN     OUT      IN      OUT      ANGLE     (cc)
                           (mm)   (mm)    (sq.cm) (sq.cm)    (deg)
 
       BARREL     60.0     29.5   33.2      6.83    8.66
         1       157.8     33.2   39.3      8.66   12.13      2.2      163.2
         2       171.5     39.3   87.2     12.13   59.72     15.9      564.6
         3       240.4     87.2  122.2     59.72  117.28      8.3     2089.0
         4        39.2    122.2  110.8    117.28   96.42     16.5      418.2
         5        63.2    110.8   79.5     96.42   49.64     27.8      453.4
         6        51.5     79.5   33.5     49.64    8.81     48.1      136.3
        TAIL      86.7     32.5   32.5      8.30    8.30
 
 
      ENGINE PERFORMANCE INDICATORS
      -----------------------------
 
      SPEED     POWER    TORQUE       POWER    TORQUE
      (rpm)      (kW)     (Nm)         (hp)   (ft lbf)
 
       1000     0.370     3.535       0.496     2.607
       2000     0.599     2.860       0.803     2.109
       3000     1.051     3.344       1.409     2.467
       4000     2.197     5.244       2.946     3.868
       5000     5.033     9.612       6.749     7.090
       6000     7.270    11.570       9.749     8.534
       7000     9.548    13.026      12.805     9.607
       8000    13.193    15.748      17.692    11.615
       9000    15.052    15.970      20.184    11.779
      10000    11.601    11.078      15.557     8.171
 
      SPEED      IGNITION TIMING       AIR FUEL
      (rpm)       (degrees BTDC)         RATIO
 
       1000            24.5              13.00
       2000            24.5              13.00
       3000            24.5              13.00
       4000            24.5              13.00
       5000            24.5              13.00
       6000            24.5              13.00
       7000            24.5              13.00
       8000            24.5              13.00
       9000            24.5              13.00
      10000            24.5              13.00
 
      SPEED     MEAN EFFECTIVE PRESSURES  (atm)
      (rpm)     BMEP     PMEP     FMEP     IMEP
 
       1000     1.772    0.082    0.029    1.884
       2000     1.434    0.092    0.059    1.585
       3000     1.677    0.100    0.088    1.865
       4000     2.629    0.233    0.117    2.979
       5000     4.820    0.408    0.147    5.374
       6000     5.801    0.501    0.176    6.478
       7000     6.531    0.539    0.205    7.275
       8000     7.896    0.579    0.234    8.710
       9000     8.008    0.549    0.264    8.820
      10000     5.554    0.418    0.293    6.266
 
      SPEED   FUEL CONSUMPTION        FLOW RATIOS           SCAVENGE  RATIOS
      (rpm)    (BSFC: lb/hph)     DELIVERY    EXHAUST       MASS      VOLUME
 
       1000         1.032         0.337934   0.337727       0.337      0.340
       2000         1.032         0.273492   0.273015       0.273      0.274
       3000         0.943         0.292168   0.294875       0.300      0.301
       4000         0.899         0.436934   0.442361       0.443      0.444
       5000         0.941         0.838447   0.838550       0.839      0.867
       6000         0.872         0.935362   0.935491       0.935      0.982
       7000         0.929         1.121026   1.120974       1.121      1.200
       8000         0.831         1.213048   1.213049       1.213      1.308
       9000         0.774         1.145004   1.145011       1.145      1.257
      10000         0.913         0.936711   0.936364       0.937      0.941
 
      SPEED              EFFICIENCIES             PERCENTAGE ENERGY LOSS
      (rpm)     SCAVENGE   TRAPPING   CHARGING      IN EXHAUST SYSTEM
 
       1000       0.488      0.668      0.226             32.98
       2000       0.424      0.684      0.187             53.57
       3000       0.477      0.712      0.213             41.77
       4000       0.574      0.671      0.297             26.86
       5000       0.774      0.577      0.483             11.45
       6000       0.840      0.591      0.553              9.84
       7000       0.875      0.532      0.597              8.10
       8000       0.879      0.585      0.710              7.02
       9000       0.864      0.636      0.728              7.46
      10000       0.834      0.548      0.513              7.17
 
                   PEAK CYLINDER         TEMPERATURE LIMITS AT CENTRE
      SPEED   PRESSURE    TEMPERATURE    OF THE EXPANSION CHAMBER (F)
      (rpm)     (atm)         (F)           MEAN      LOW      HIGH
 
       1000     27.85       2276.12        449.4    446.9     456.7
       2000     25.45       2150.92        446.0    441.7     455.2
       3000     27.04       2296.55        494.1    484.4     509.9
       4000     36.22       2792.18        552.4    536.4     577.5
       5000     48.61       3263.44        613.9    589.7     654.1
       6000     55.03       3588.20        671.9    644.6     730.1
       7000     58.13       3719.44        648.4    611.5     719.2
       8000     69.42       3783.74        711.5    663.9     780.1
       9000     71.32       3737.32        741.3    686.8     816.5
      10000     48.03       3449.45        633.3    597.4     686.3
 
      The Specific Time Area of a port is the sum of all port areas
      over time divided by the cylinder swept volume.
      The units sec/metre and sec.sq mm/cc are equivalent.
 
              SPECIFIC PORT TIME AREA
                (sec/metre x 10000)
      SPEED    INLET   TRANSFER   EXHAUST                                                                               
      (rpm)                                                                                                             
 
      1000    1245.2     623.9    1031.8
      2000     622.6     311.9     515.9
      3000     415.1     208.0     343.9
      4000     311.3     156.0     258.0
      5000     249.0     124.8     206.4
      6000     207.5     104.0     172.0
      7000     177.9      89.1     147.4
      8000     155.7      78.0     129.0
      9000     138.4      69.3     114.6
     10000     124.5      62.4     103.2
 
  Elapsed time: 24.00 seconds
Title: Re: GT380 ground up build
Post by: teazer on Jun 27, 2018, 18:59:07
That's starting to look more normal.  How did you measure the two volumes?  They both look a little low.  And be careful with that ignition timing. 24.5 is rather high for 9,000 rpms.

And you are correct, all bike projects are a compromise between different competing constraints. Just out of interest, you might want to go to Jennings or Bimotion to see if all three ducts are correctly optimized in terms of time-area.
Title: Re: GT380 ground up build
Post by: 1fasgsxr on Jun 27, 2018, 19:30:01
Thatís nuts!
The amount of time that must have gone into the conception of it must be staggering
   and it don't sound like it's going to fly apart....
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 28, 2018, 07:30:48
to get the combustion chamber volume I put the cylinder on the crankcase and sealed the area between the piston and cylinder with some plasticine, then added the head gasket and used a burette to fill the chamber to the edge of the plug hole, I know that'll change a bit with a plug installed but it was the way I know to approximate it.  for the crankcase I drilled a hole in an old piston, installed everything, blocked off the oil injection port, clayed up the transfer sections and the intake port, filled the crankcase to the hole in the piston at bdc, then drained the oil out the crankcase drain and measured that.  the timing was determined by the manual, which has it set to 3mm btdc, which translates to 24.5 degrees, I don't know if it advances or not, didn't have a chance yet to look at the timing plate, my assumption from working on a few mopeds is that it does not, it's going on the dyno when finished, so it'll give us a chance to play with the timing if it starts pinging.  I'd assume that timing indicates a very slow burn due to the nature of the design, if this were a longer term project I'd probably dive right in and copy something like a tm125, probably start breaking rods at that point though
Title: Re: GT380 ground up build
Post by: themotoworks on Jun 30, 2018, 12:34:52
(http://i1266.photobucket.com/albums/jj540/smp4616/gt380june_zpsyqrej63b.jpg)
(http://i1266.photobucket.com/albums/jj540/smp4616/gt380june2_zpspa4nhf1a.jpg)

made more progress into the design, the rear linkage is basically set, it took me a while to figure out how best to make a light and compact link, fabricating it from a tube with arms welded on seems to be the best way.  I also had a lot of trouble getting a shock configured the way I initially designed it, so I redesigned based on a stock ducati 821 shock, it's still tuned well for anticipated weight, but not quite as progressive, was still able to use up all shock travel for 130mm rear wheel travel.  also figured out how to mount the rearsets as efficiently as possible, this was tough because of how wildly off center the rear engine mounts are, this engine was a pain in the ass platform to start with, but I think it'll work out well. 
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 03, 2018, 10:14:43
finished the design work, minus maybe some little spacers and stuff, going to start machining this week since no one expects much with the 4th falling right in the middle of the week
 ;D


(http://i1266.photobucket.com/albums/jj540/smp4616/gt380final_zpssa3stb2h.jpg)
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 05, 2018, 08:13:31
got some sketches back from Jeremy, I am really liking the concept, can't wait to finish the mechanical part of the build and start fabricating the pretty stuff. 


(http://i1266.photobucket.com/albums/jj540/smp4616/Image_zpsv7kknr3n.jpeg)
Title: Re: GT380 ground up build
Post by: advCo on Jul 05, 2018, 10:26:44
got some sketches back from Jeremy, I am really liking the concept, can't wait to finish the mechanical part of the build and start fabricating the pretty stuff. 


(http://i1266.photobucket.com/albums/jj540/smp4616/Image_zpsv7kknr3n.jpeg)

I love the sketches. What are you going to do about the exhaust?
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 05, 2018, 10:47:15
the expansion chambers I designed will probably be a bit longer, but the exhaust isn't the first thing my eye goes to, so I feel like changing from the pictured design in that area won't alter the overall design much
Title: Re: GT380 ground up build
Post by: The Jimbonaut on Jul 05, 2018, 10:51:21
Those sketches look great - I love the look of that front fairing, and the lines make the bike look like it's doing the ton standing still.  Very nice!
Title: Re: GT380 ground up build
Post by: advCo on Jul 05, 2018, 10:59:03
Just curious, as the pictured exhaust looks like something off a new FZ07 or something. The chambers on a triple can be one of the coolest aspects of these builds.
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 06, 2018, 17:48:12
(http://i1266.photobucket.com/albums/jj540/smp4616/IMG_20180706_164418_edit_1530909868330_zpsj1vcadfg.jpg)

finished the head tube and bearing cups, total pain in the butt, had to machine, weld, then finish machine to make sure welding didn't warp the bearing holders (it does way more than you'd think!), but they came out round and .0005" under bearing OD, the bearings went in with a small hammer and aluminum drift, nice and snug but not too tight.  going to set up the engine and a way to clamp my mount plates to the frame jig, then start finishing the frame, probably another day on it
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 07, 2018, 19:15:15
(http://i1266.photobucket.com/albums/jj540/smp4616/Mobile%20Uploads/IMG_20180707_133917438_zpszwx7opfa.jpg)
(http://i1266.photobucket.com/albums/jj540/smp4616/Mobile%20Uploads/IMG_20180707_163259750_zpseiczaszn.jpg)

almost done with the frame, you can see where it attaches to the aluminum subframes at the rear, also a pic of my cutting setup, does real nice work, if I design a frame in SW I can notch all the tubes within a few thousandths, putting the frame together leaves no gaps to fill, a bit time consuming to get all the data from the computer, but definitely worth it
Title: Re: GT380 ground up build
Post by: jpmobius on Jul 07, 2018, 21:27:56
Could you elaborate on your thinking regarding the decision to create the aluminum brackets? I realize there is a lot going on in this area, and can see machining the aluminum potentially being simpler than creating a steel fabrication, but don't reckon there to be weight savings.  This wouldn't be my preferred location for a bolted connection, but as you have obviously put a great deal of thought into your choices it would be helpful to hear how you arrived at some of them.  Lovely work all around!  I also am a big proponent of building a virtual model and creating parts directly from it - excellent fitting parts become a function of layout skill!
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 07, 2018, 22:32:47
it had a lot to do with aligning the engine, swingarm, shock linkage and steel frame with less work than trying to do the same with a weldment, with a weldment I'd be looking at multiple jigs and probably finish machining of the welded assembly to guarantee alignment of the components, this saved all that work and might actually be a bit lighter than the steel spiderweb that would be the result otherwise, the plates are actually pretty light
Title: Re: GT380 ground up build
Post by: RR100 on Jul 07, 2018, 23:13:09
Bimota frequently used steel trellis with aluminum swinger plates. The MV augusta Brutale's have this construction as well.
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 09, 2018, 19:58:54
(http://i1266.photobucket.com/albums/jj540/smp4616/Mobile%20Uploads/IMG_20180709_175555428_HDR_zps6x86xygt.jpg)

finished the frame except a couple little spots that can be done off the jig. 
Title: Re: GT380 ground up build
Post by: jpmobius on Jul 10, 2018, 11:27:12
Looks like a considerable volume in the big tubes.  Oil tank? 
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 10, 2018, 12:08:03
yeah, oil in the cross tube and gas in the main tube, it adds another .75 gallons, so the fuel cell under the bodywork can be smaller
Title: Re: GT380 ground up build
Post by: doc_rot on Jul 10, 2018, 20:01:14
Very nice. Reminiscent of the EGLI frames
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 11, 2018, 14:09:38
finished machining the axles for the swingarm, they do double duty and hold the rearsets as well, thus the smaller outrigger bearings, most of the rearset force winds up on those bearings and the rearset hanger is kept from rotating by a screw going into the rear aluminum plates... kinda involved but when it's all laid out well it goes together pretty easy, also finished the rear rocker, still waiting on getting the rocker bearings in but they should be here tomorrow and I can start putting the rear end together, will start machining swingarm parts today too


(http://i1266.photobucket.com/albums/jj540/smp4616/Mobile%20Uploads/IMG_20180710_114835_199_zpskjw8nosz.jpg)
(http://i1266.photobucket.com/albums/jj540/smp4616/Mobile%20Uploads/IMG_20180711_120644_140_zps3xk8tvjj.jpg)

Title: Re: GT380 ground up build
Post by: jpmobius on Jul 11, 2018, 17:01:53
That is going to be a slick set up - hope you will provide a thorough description of how all the bits are fixed in place.  Tapered rollers are pretty unusual for a swing arm pivot, though I have often thought of doing this myself as it would seem the optimal means to eliminate lost motion in this very important pivot.  Love the rollers for the foot controls, I have built rear sets doing this very thing (though not coincident with or part of the swing arm axle) and never fail to be pleased with the still perfect and zero play precision motion after many years of use!  Lovely old school fab work on the rocker as well - after seeing the aluminum frame plates I expected you would carve up another block for this part.  I personally am partial to the "built by hand" look of fabrications like this which seem to becoming scarce with so much CNC work being so prevalent - nice!
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 11, 2018, 19:34:39
I think I might actually switch back to ball bearings, having the swingarm mounted the way it is due to the engine mounts being waaay off to one side made things very complicated and the sealing system for the thrust bearings is probably going to fail in service, ball bearings are way simpler and still handle the anticipated loading, but with less margin than the tapered ones, but if the thrust bearings leak grease and pick up road grit asap, then that's no good either... good thing there's mcmaster, swapping to ball bearings is just a day away.  love those guys
Title: Re: GT380 ground up build
Post by: themotoworks on Jul 13, 2018, 12:56:48
(http://i1266.photobucket.com/albums/jj540/smp4616/Image-16_zpsuujbotve.jpeg)
(http://i1266.photobucket.com/albums/jj540/smp4616/Image6_zpsuzgmt5ou.jpeg)

got some more sketches, the design is getting a lot closer to 100% done, starting to convert the bodywork to actual shapes now, kinda interesting working from an artists renderings and to figure out how to make an actual shape that conforms to what the various views are showing...
Title: Re: GT380 ground up build
Post by: jpmobius on Jul 13, 2018, 15:06:50
Going to be a good looking motorcycle.  As I think someone else mentioned, don't underestimate the exhaust - it will take up a very large piece if visual real estate not present in the renderings!
Title: Re: GT380 ground up build
Post by: RR100 on Jul 13, 2018, 19:08:01
Perhaps I missed the discussion, but have you decided upon material and construction method for the bodywork?
As jp said, pretty bike. The rendered muffler placement really fits aesthetically, but seems impossible packaging for a two stroke no?

Good stuff in any event.