Overlap should lower compression as you get blowby from my understanding.


-Zach

 

You need to re-understand. Blowby is the amount of air "blowing-by" the cylinder rings, which does affect compression, but has nothing to do with cam events. Excessive blowby, which is undesirable in any amount, is caused by poor cylinder wall to ring fit, which can be a result of bad tolerances, warpage, wear, etc. Large overlap causes intake charge dilution at low firing speeds, but has nothing to do with static compression.

 

i was edumecated in the rotary world. So when i said blowby i was talking about pressure released from the overlap of the exaust and intake stroke. (there are no pistons, rings or valvetrain)

thinking about it on a 4stroke motor this probably won't happen though, so it won't effect compression. (on a rotary, you pick up large gains by increasing the overlap between the exaust and intake stroke, but loose compression from it) Was forgeting that the evo motor is not a 2 stroke :P

 

Ah I see. Yes the inferior 4 stroke is quite different. I myself need to dig into some good papers on 2-stroke motors and rotaries one of these days...

 

Exhaust scavenging is what you are talking about It isn't called "blow-by" even on a rotary engine.

 

ohh but i think he can call it blow-by if he wants to. check it out i can call it blow-by.


"overlap causes blow-by"--i just said it. hahahahhahaha

damn i was hoping that the evo9 pistons were going to be higher compression. do the heads have the same volume between evo 8 and 9? and also same volume as dsm heads?




Eddie Rosado

 

I used the term blowby because it was the only one i could think of to describe exhaust passing by. but you are right, wrong term. My original thinking is overlap could lower compression like on a rotary. But that is not the case with a 4strock.

Not sure i agree the correct term is scavaging. it should just be overlap and i shouldnt have evey used blowby.

Scavenging to me is outside the engine. has more to do with tuned length exhaust. Overlap is more of a push out the exhaust, where scavenging would be pull from the exhaust. So related, but different?