Ok, 1 more theoretical ?

[Sprocket1]

and then I'll quit. Maybe. It is hard on a gasoline engine to run it without a muffler. Why?

[normde2001]

OK....Why? The most powerful gasoline engines I know of , (top-fuel dragsters, 5,000+ hp), run without mufflers.

[Sprocket1]

A muffler causes backpressure. Backpressure is needed to keep the piston pushing down on the connecting rod bearing. If it didn't the piston will have a minute amount of overtravel due to bearing clearance. It is called "slap" I think. The engines you are refering to are extremely short lived. They measure "worn outness" in seconds not hundreds of hours.

[DieselD]

Yes, you'll loose exhaust valves.
What do I win?
Danny

[bgott]

I haven't heard or read that one and I've been a mechanic for durn near 30 years. Even with back pressure you would get that slap effect when the piston and rod changed direction. If you had enough back pressure to push the piston down it would barely run if it ran at all. You also have a pressurized oil film for a cushion. Why would it affect a gasoline engine and not an unmuffled non- turbocharged diesel engine? I think someone blew some smoke up your hiney. [img]/forums/images/graemlins/blush.gif[/img] I've always heard that you didn't want to run an engine without pipes from the manifolds. It had nothing to do with back pressure, supposedly when you shut it off cold air could run up the manifolds and warp the exhaust valves. I have ran the pee out of a few engines without exhaust pipes on cold days and shut them off and never had a valve problem due to cold air intrusion.

[Sprocket1]

That's what I was taught at Allis-Chalmers Engine school 30 some years ago. I did a google search for engine backpressure. Seems everyother result argued the need for or against backpressure. I'd say that is a subject that will be argued for eons.

[MossRoad]

<font color="blue"> It is hard on a gasoline engine to run it without a muffler </font>

Without a muffler or without an exhaust manifold?

[slowrev]

Not really sure about the engine, but I do know it is hard on my ears. I like good mufflers and good hearing [img]/forums/images/graemlins/smile.gif[/img]

[jpr62902]

What if you replaced the stock exhaust with a less restrictive (louder) exhaust system (Cat back)? Would that cause engine damage?

[kemartin3]

I'm not an engineer, but for what it is worth. The amount of backpressure affects the performance of the engine, both overall horseposer and torque, and the amount of each at a given RPM. A term you may hear is a "tuned exhaust." It is done in lots of ways: pipe diameter, pipe length, mufflers, etc. On race cars (e.g., NASCAR) there are often multiple pieces of exhaust pipe of different lengths and diameters to get the desired torque and horsepower "curves." An important piece is having the same effective pipe length for each cylinder, hence the funny contorted bends you often see in aftermarket headers. I've seen a couple of books that explain all of the math needed to do the job right. Made my head hurt.

Kevin