Engine function and performance - a comprehensive explanation

You're not the only one who's interested in the finer details...

http://www.x386.net/TTR/tech/cgi-bin/motorsim.cgi

Still working on factoring in cam profile influence on the final output numbers, along with intake/carb sizing. Exhaust is going to have to be it's own sim I bet... Plus bore/stroke ratio impact... so much math to sort out.

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Originally Posted by Kurlon

You're not the only one who's interested in the finer details...

http://www.x386.net/TTR/tech/cgi-bin/motorsim.cgi

Still working on factoring in cam profile influence on the final output numbers, along with intake/carb sizing. Exhaust is going to have to be it's own sim I bet... Plus bore/stroke ratio impact... so much math to sort out.

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oh man.. I think that might be a larger task than you realize.. the impact of proper intake and exhaust port&runner tuning with matching cam profile can create volumetric efficiencies of greater than 1.. and that doesn't even factor in pumping losses, friction losses based on thrust vector (or maybe it does factor that with the rod length to stroke length ratio..)

my head hurts even trying to imagine factoring it all in together in an equation!

i also see nothing factoring in compression ratio..

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Originally Posted by Cerberus

oh man.. I think that might be a larger task than you realize.. the impact of proper intake and exhaust port&runner tuning with matching cam profile can create volumetric efficiencies of greater than 1.. and that doesn't even factor in pumping losses, friction losses based on thrust vector (or maybe it does factor that with the rod length to stroke length ratio..)

my head hurts even trying to imagine factoring it all in together in an equation!

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Heh, one piece at a time. Pumping losses and friction due to thrust angles are not factored in right now, at least not specifically. There is a generic 'powertrain loss' fudge factor that is user settable, defaults to 85% pass through, although some dyno comparisons against my model suggest 90% is more accurate on pitbikes.

if you have a dyno, you can do a couple different negative HP runs to actually see how much you are losing

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Originally Posted by RandyO

waaaay too much info, do you actually expect anyone to read all the way thru?


function of engine --- to make the bike go
performance is related directly to how much you twist the throttle


that's all you need to know

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Unfortunately, for those who only know this much, they get to go straigh to the dealer to get raped when the bike doesn't do what they expect it to when they twist the throttle. This is one of many reasons I prefer to know as much as I can about motors/mechanical things

Let's get back to the 90 degree crankshaft. I have read (as many have) that big bang maotors are more about getting a better vibration frequency to allow revs to climb past the 17K mark. Not to rest the tire.

I think they have found that traditional I4s start to really fight themselves as the revs climb.

It's all about spinning a flywheel.

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Originally Posted by Paul_E_D

Let's get back to the 90 degree crankshaft. I have read (as many have) that big bang maotors are more about getting a better vibration frequency to allow revs to climb past the 17K mark. Not to rest the tire.

I think they have found that traditional I4s start to really fight themselves as the revs climb.

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Originally Posted by Paul_E_D

Let's get back to the 90 degree crankshaft. I have read (as many have) that big bang maotors are more about getting a better vibration frequency to allow revs to climb past the 17K mark. Not to rest the tire.

I think they have found that traditional I4s start to really fight themselves as the revs climb.

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from everything i've read, the big bang motors have to made stronger internally (and internally counter balanced) to handle power pulses that happen in close proximity to each other instead of being equally spaced.. and stronger typically equals heavier.. which equals lower redline..