Straight Pipe

I have always heard that running a straight pipe – no muffler- is not good practice because there has to be some backpressure in the exhaust system or you will burn valves, pistons, bearings and whatever. That has never made sense to me and I do not see any reason it should be true. Other than being noisy I don’t see the problem with running a straight pipe.

Without considering noise or air pollution and keeping the conversation to an M, H or IH300/350 or similar, does anyone know for a FACT that it hurts a gas engine to always run without a muffler.

Diesel any different?

there are alot of factors top race engine builders have to concider when building an engine and to acheve the magical hp rating they look at stoikial metric effencie I think thats how it's spelled, any ways this factors in valve over lap and exhaust scavaging and so on now a engine that has the exhaust and the intake in the same casting like on the farmalls and most industrial engines and the runners are not equal length. so I guess what I am saying is if a strait pipe works for you and you are alredy def go for it if not then don't my experince has been the old stanly mufflers not as god for sound as a good nelson muffler industy muffler also they are made just down the street from me!!!

Mowing hay around a big sycamore tree, one of the branches caught it and broke the manifold.

So I always run a muffler to save a manifold. I know the manifold was rotten but ti would sure have lasted longer with a muffler to bend instead of a piece of pipe.

A tuned exhaust does make an engine breath better, just as too long or too short makes it more difficult.

Beside burning valves, in engine run without an exhaust pipe each cylinder has to start the gas moving against still air, where if the pulse from the cylinder before it was moving out the exhaust pipe, it helps pull the exhaust from teh new cylinder.

Headers on an engine (assuming they are designed using computational fluid dynamics and are real competition components) use exhaust scavenging to time the pressure and partial vacuum acoustics of the pipe/s so that at particular engine RPM the partial vacuum is pulling the last exhaust out of the cylinder (during overlap) and creating an easier entry of charge. Unless the engine/cam is pretty far toward the racing end of the spectrum, there will be mild effects of this pulse related advantage. Big huge large diameter pipes and headers are only used on machines that can produce enough flow to create high velocity in the big pipes. Low speed engines with modest cylinder displacement, shrouded valve placement, and small valve area will be little affected.
JimN