GT380 ground up build

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?
 
themotoworks said:
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.
 
The more volume between the piston port and reed valve, The longer the delay between piston port opening and read valve opening.

Let’s 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 rpm’s 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.
 
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
 
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?
 
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.
 
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?
 
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.
 
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
 
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
 
farmer92 said:
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
 
irk miller said:
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

That’s nuts!
The amount of time that must have gone into the conception of it must be staggering
 
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
 
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.
 
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
 
gt380june_zpsyqrej63b.jpg

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.
 
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


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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.


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