ESE's works engine tuner

[aljaxon]

I do it like this, with the depth gauge of the caliper in the top corner of the exhaust port, against the piston.
Attachment 354309










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at first i looked at it and thought thats wrong cos i and my 2 tuning pals been measuring to the centre of the port at piston end and centre at flange end to "average" out the distance. and then when i thought why you'd gone to the top i realised thats when the waves start and by the middle, where im measuring those waves are inconsequential.
its only a couple of mm and in theory my pipes will be shorter and revving 50rpm or so higher.
but bottom line is i and my pals have been measuring wrong.
cheers frits.

[Frits Overmars]

.It is always a worry drilling holes here as it may loosen the crank pin.

Your concern is justified if the amount of remaining material between the crankpin bore and the balancing bores is smaller than half the crank pin diameter.
The effect of those balancing bores is proportional to their distance from the crankshaft center. Drilling those holes a little further away from the crank pin, and much closer to the outer edge of the crankshaft would have had more effect, i.e. you would have been able to make do with smaller bores.











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[wobbly]

Re the duct length - this as you say only makes a small difference , but Neels in his guide for EngMod uses the duct centerline length ie mid port height to mid exit face.
I have always used the average of the roof length and the floor length - measured as Frits described , from the port edges to the exit center.
Saying that the top timing edge is where the wave starts is correct , but we also have a return wave that begins occurring when the piston is near BDC - and that length is shorter.
So both the BDC and EPO lengths have an effect on that wave timing as seen by the port face.

This varying length effect also applies to a reed blocks intake length in the sim.
The length from the blocks mounting face to the petal tip is effective when the reeds are closed , but when fully open the length from the mount face to the beginning
of the port in the block is effective. In testing a CR125 with a fully instrumented dyno using TFX data logging for a PhD project I found that the effective average intake tract length worked
in reality from the bellmouth with end correction , to a point on the reed block ports that was 2/3 of the distance from the mount face to the tips.
This replicated perfectly in the sim , the wave action within the intake as seen on the instrumented engine.

[porttiming124]

Re the duct length - this as you say only makes a small difference , but Neels in his guide for EngMod uses the duct centerline length ie mid port height to mid exit face.
I have always used the average of the roof length and the floor length - measured as Frits described , from the port edges to the exit center.
Saying that the top timing edge is where the wave starts is correct , but we also have a return wave that begins occurring when the piston is near BDC - and that length is shorter.
So both the BDC and EPO lengths have an effect on that wave timing as seen by the port face.

This varying length effect also applies to a reed blocks intake length in the sim.
The length from the blocks mounting face to the petal tip is effective when the reeds are closed , but when fully open the length from the mount face to the beginning
of the port in the block is effective. In testing a CR125 with a fully instrumented dyno using TFX data logging for a PhD project I found that the effective average intake tract length worked
in reality from the bellmouth with end correction , to a point on the reed block ports that was 2/3 of the distance from the mount face to the tips.
This replicated perfectly in the sim , the wave action within the intake as seen on the instrumented engine.

Woobly.
Can you explain the (End Carburetor Correction) ?
What exactly is it for?

[TZ350]

Had a couple of interesting bikes on the dyno today.

[wobbly]

An intake wave travels up and down the tuned length , and when a positive wave reaches atmosphere it is not reflected back directly from the face of the bellmouth.
The actual reflection point is past the end - as air is " soft " .
For a bellmouth inlet on a carburetor the end correction is a parallel length added to the end diameter that is 0.25 X the bellmouth inlet diameter.
So for a 38 Dia carb the end correction added to the bellmouth is a parallel 9.5mm section.

I know that BSL bike quite well - did it hit 155 RWHp like it used to.

[peewee]

Aha , so the Serval is a different animal , maybe those port timings are low with the BDC in the right place - I had not seen that actual setup sheet before.
The 68/64 normal Cub is set up with a 120 rod and a option TRX piston.
Shit thats a very short rod on a big stroke - even the original RD400 with the 62 stroke was limited by those short 115 rods.
But yes stagger with the A opening first , the next two the same lower height and the boost lower again - works very well.
Having the ports all low like that makes it easy to get all the STA numbers correct very easily as its not plated.
And my choice would be the Banshee piston with the 5mm spacer to get some case volume happening.
CrankWorks are just as bad as plenty of others at using all the same components for a huge bunch of different combo's of stroke/rod/piston - so check what the BF actually is.

ive tried stagger of A first then B then C / D the same. i never heard of A first then B/C same then D. is it something new ? whats the principle behind it ? did you do 1* steps ?

[wobbly]

The CPI cylinders all use the same configuration with an A port , then the B & C are like a big B port with a divider in it. Then the 2 x D ports are basically a normal boost port
again with a divider.
So I opened A first , then treated the B & C as a normal B only and made them the same timing - then as usual the boost ports lowest.
And the stagger was 1.8* A to B/C then 1.6* B/C to D.
Later I did Cheetah's with a PV , they had reverse stagger with the A low and 1* rise to the B/C/D same as the RSA.
Having the PV allowed very large triangular Aux ports helped by the low A - the STA's then matched well due to the large area of the 6 high ports.

[Frits Overmars]

Woobly. Can you explain the (End Carburetor Correction) ? What exactly is it for?

For a bellmouth inlet on a carburetor the end correction is a parallel length added to the end diameter that is 0.25 X the bellmouth inlet diameter.

This picture is from my 'FOS Software' and 'FOS tips & concepts'. You can find it at https://1drv.ms/u/s!Atyzb5b7jtWNmVcX...5eKjL?e=nxuw41
Everything that I make available there or via open forums such as KiwiBiker and Pit-Lane, or even via Fakebook, may be freely used and distributed.
So Wob, you already did a fine job with words, and you are very welcome each time you feel like illustrating your words.

[wobbly]

Thanks so much for your input Frits - not bad for a " Dutch motor mechanic ". I wonder if the evil eye of the Dragonfly is upon us still.
I see he has his very own Forum , where as Jaguar he rules supreme over a bunch of fawning acolytes that never dare transgress by disagreeing with anything spewed forth by his Royal Highness.

[skako]

Hi,
Attached is a graph simulated in EngMod2. The graph from EngMod serves me as a reference value for comparison with the graphs I get from my simulator (which is based on the first book by Prof. Blair).
Vannik already warned me earlier that the absolute values I get from that simulator can deviate significantly from reality.
I still "play" with that simulator because I can change its code. With minor or major additions to the code I run it through the ideal situation.
I wanted to see what happens at ( 0.666 x RPM_ power_ max ) if I remove the negative influence of pressure from the exhaust pipe in the BDC position, when the cylinder is maximally open.
However, I can't test 2-nd situations with EngMod2 to get good and accurate values.
EngMod is not designed that way. With a few lines of the author's programming code, EngMod would surely do it. I need a benchmark, so I can accept or reject the guidance from my simulator.
Perhaps this does not belong directly to tuning, but it still has something to do with tuning.

[porttiming124]

An intake wave travels up and down the tuned length , and when a positive wave reaches atmosphere it is not reflected back directly from the face of the bellmouth.
The actual reflection point is past the end - as air is " soft " .
For a bellmouth inlet on a carburetor the end correction is a parallel length added to the end diameter that is 0.25 X the bellmouth inlet diameter.
So for a 38 Dia carb the end correction added to the bellmouth is a parallel 9.5mm section.

I know that BSL bike quite well - did it hit 155 RWHp like it used to.

Thank you Woobly

[porttiming124]

This picture is from my 'FOS Software' and 'FOS tips & concepts'. You can find it at https://1drv.ms/u/s!Atyzb5b7jtWNmVcX...5eKjL?e=nxuw41
Everything that I make available there or via open forums such as KiwiBiker and Pit-Lane, or even via Fakebook, may be freely used and distributed.
So Wob, you already did a fine job with words, and you are very welcome each time you feel like illustrating your words.

Thank you Frits

[porttiming124]

I took the formulas from Frits' picture.
For a 44 mm carburetor that gives me an external diameter of 141 mm.
the center center of the 2 cylinder in-line engines that I work have 118mm so it overlaps.
What do you recommend to me?
I cheat the formulas to have an external diameter of 118 mm or I cut a part from each so that they don't touch each other.

[wobbly]

Many engines have the same issue - cut a small flat on each bell so they will sit on the smaller centers.
Does not seem to affect performance at all.