Ok...I asked about what scavenging was, waaay back when...I have another automotive physics question.

Ok...if scavenging is achieved by the entire exhaust system working together, then why would it be beneficial to run open-head (that is, to run no exhaust at all, have nothing past the exhaust manifold)? Wouldn't that create an extreme lack of back-pressure? thanks

 

Yes there would be practically no backpressure at all. However you can run into problems. First off it would be very easy for contaminants to get into the motor. Second, that extreme lack of backpressure can cause air to go back into the exhaust ports, and you can suck a valve...no good h:

 

I can't think of anything beneficial about that. You'd heat your engine bay like MAD, poor flow, reversion, etc, etc.

 

Actually, with an open head, you wouldn't get reversion, you'd get diversion, the sound energy from the exhaust would go wasted as it's released in a chaotic manner. This obviously does nothing to help scavenging, so what do you get? You get no thermal barrier in place for the valves since there's no direction to the heat and sound to create a rolling "wall" of air that helps scavenging, and instead you can allow ambient temperature air [which is much lower than the combustion temperature] to make contact with the valve face, which can cause all sorts of nastiness such as warping, and that air can also carry contamination into the engine as was said earlier.

 

hmm...guess I should tell Roland that he should keep the exhaust on his teg next time he runs...nah, hehehe:naughty: let him learn by his own vices