porting/durations/peak-power-RPM needed

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Joined: Fri Feb 17, 2017 12:49 pm

porting/durations/peak-power-RPM needed

Postby jaguar » Fri Feb 17, 2017 4:55 pm

hi guys
I've already made spreadsheets for
1) calculating squish velocity http://www.dragonfly75.com/moto/sqVelocity.html
2) balancing the crank (2 stroke or 4 stroke) http://www.dragonfly75.com/moto/crankbalance.html
3) designing a boost bottle http://www.dragonfly75.com/moto/YEIS.html
4) designing expansion chambers http://www.dragonfly75.com/motorbike/portsMS.html

Now I want to design a calculator for correct engine porting. So far all that's been available to us are general guidelines and the time-area formulas made for old GP bikes. I dislike the latter because the formula for the exhaust port uses the whole port instead of only the blowdown area. That is OK for the old style of engine with one squarish exhaust port but not for bridged ports or ones with two auxiliary ports. Also its transfers formula uses the whole port open time whereas I've observed on crankcase pressure traces that for every 1000 RPM over 5000 that the end of its positive pressure lasts 5 degrees more past BDC. So I consider that the true "transfer time" which should be the only time put into the formula. I think my formulas are fairly close now but I want a few good engine examples to go by to get a good running average for the correction factors in each formula.
Each example needs:
A) a port map with dimensions of the ports
B) exhaust and transfer/boost durations
C) peak power RPM from either a dyno or just seat of the pants going uphill and noting at what speed/gear the power starts to drop off. Just knowing the speed and the number of crank rotations for every rotation of the rear tire in said gear I can figure out the RPM of its peak power (beyoind which the power starts to fall).
I sell my spreadsheets but this one will be free. And every one who gives me A/B/C will get a free one.

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Re: porting/durations/peak-power-RPM needed

Postby Areomyst » Wed Feb 22, 2017 11:47 am

Hi jaguar,

I remember you from the MacDizzy forums. I can provide some of that information eventually. My Derbi GP1 project is going through different stages of porting, and I'll be dyno testing it, etc... I can't make any promises on timeframe though, as I'm terribly busy with family life and work. I'm interested to see what you come up with.

"The more a man learns, the more he realizes how little he knows."

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