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Author Topic: GT380 ground up build  (Read 4660 times)

Offline CrabsAndCylinders

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  • Posts: 1978
  • Careful With That Axe Eugene
Re: GT380 ground up build
« Reply #20 on: Jun 03, 2018, 01:15:51 »
That is pure motorcycle porn, love it!
Lighter, Quicker, Faster.
ZX-14, 900F x 2, 1100F, R100, CBR600, SR500, GT500, RZ350, KZ1000 x 2, Moto Guzzi Lemans lll, CBX550, RD 350, 750 SOHC police special, RG250, TL1000R, GT750, KTM Super Duke 1290 R, Harris/Z-1, Norton 750 Commando, Green 77 KZ650

Offline themotoworks

  • Posts: 97
    • the motoworks
Re: GT380 ground up build
« Reply #21 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?

Offline farmer92

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Re: GT380 ground up build
« Reply #22 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.

Offline farmer92

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GT380 ground up build
« Reply #23 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.
« Last Edit: Jun 12, 2018, 20:23:27 by farmer92 »

Offline themotoworks

  • Posts: 97
    • the motoworks
Re: GT380 ground up build
« Reply #24 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

Offline teazer

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Re: GT380 ground up build
« Reply #25 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?
 
« Last Edit: Jun 26, 2018, 21:41:32 by teazer »

Offline teazer

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Re: GT380 ground up build
« Reply #26 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.

Offline themotoworks

  • Posts: 97
    • the motoworks
Re: GT380 ground up build
« Reply #27 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?
« Last Edit: Jun 26, 2018, 21:56:44 by themotoworks »

Offline teazer

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Re: GT380 ground up build
« Reply #28 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. 

Offline themotoworks

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Re: GT380 ground up build
« Reply #29 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