Optimum muffler position is..? 1

[ConstantCraving]

On a performance car with a rather lengthy exhaust system, is it better to place the muffler as close as possible to the engine to allow higher exhaust pressure that far forward to blast past any restriction the muffler might pose?

Or is it better to place the muffler(s) as far to the rear as possible (at the very end is this example) and let the exhaust utilize the volume of the exhaust system ahead of the muffler(s) in any number of ways?

500ci engine, 2.5" or larger exhaust pipe, dual exhaust all the way back. No CATS.

I'm kind of favoring mufflers in the rear, so the engine is seeing no initial restriction and can exhale as it wants. The muffler for each bank being approx. 12' away from where a forward mounted muffler would be. Lots of room for that blast coming out of the engine to find its' way unimpeded in that distance..

-And because I just finished installing a couple rear mounted mufflers when the question kind of came up

 

[Fabrico]

More like about 5 to 7 feet from the engine. What is meant by "12' from where a forward mounted muffler would be"? Must be a performance limousine.

 

[NickE]

Also by putting the mufflers at the back where there is more excess space (no motor), the exaust system can be designed to take advantage of the pulses to increse VE above 100%.

Unless its a forced induction motor. Then you want as little pressure as possible.



Nick
I love materials science!

 

[Tmoose]

A long pipe with no muffler is pretty good at developing standing waves, so various notes are likely to be excited as the motor revs.
There will probably be a beauty right at cruising speed.

 

[thrashercharged]

So what is the answer? My understanding from reading the responses is that Tmoose is suggesting placing the mufflers close to the header collector to reduce standing waves for optimum silencing. Nicke is suggesting that placing the mufflers farther back can help increase VE above 100%. Why exactly does placing the mufflers farther away as opposed to closer make it easier to increase VE?

So is the answer to place the mufflers close to the header for maximum silencing and near the end for maximum power?

I assume that the farther away from the collector the mufflers are, the smaller they can be because the exhaust will have cooled and the volume is less?

Also, weren't there more responses in the thread a few days ago that disappeared? I think the original poster said something about having a 10 sec car? Were there any good responses in the lost posts? I can't recall. Why would these response be deleted/lost?

 

[Fabrico]

Few vehicles, production or race, have had much choice as to where the muffler(s) could go. Nor have the dyno people said much over the years.

There were more responses here but they weren't all friendly so the thread got rewound a bit. You didn't miss a thing.

 

[innovator]

This Vizard article will tell you (and a lot more)

http://www.geocities.com/motorcity/track/6992/vizard.html

In brief....What is important is the volume of the silencer and if it acts as an expansion chamber. If this is the case, near the engine can have benefits. If you have an expansion chamber then the silencer can go anywhere and it needs to flow 2.2cfm (not sure at what pressure) for each Bhp to not cause restriction and thus powerloss.

The expansion chamber replicates open pipes, so a large expansion of the gas pulse, causing the negative wave.

Read the article its good.

John

 

[NickE]

thrasher-

placing the mufflers further back doesnt necessarily improve VE, it provides more room for tuning length.

Nick

 

[Viper488]

I've recently found and read the Vizard article. Many websites have printed it.

If the muffler was further back that'd leave more room for the gases to expand before reaching the restriction of a typical muffler.

Vizard says tune the engine for best H/ collector length, then add the 'pressure wave terminator box' and the rest of the exhaust system. Really sounds like a 2 stroke expansion chamber doesn't it?

I'm going to weld up a pressure wave terminator box based on Vizard's article Though other than Vizard's expansion chamber theory, it doesn't appear the idea has taken off in the general high performance world does it?

He also talks about balance pipes a bit. I made one 10yrs ago and dropped .25sec from my ET..

 

[Tmoose]

I said "A long pipe with no muffler is pretty good at developing standing waves, so various notes are likely to be excited as the motor revs. There will probably be a beauty right at cruising speed."

I meant that a few times I have placed a muffler under the floor somewhere, followed by several feet of straight-thru pipe to reach the rear of the car. I judged the result
was to largely undo the muffler's silencing chores at certain speeds and create nice loud droning notes at certain rspm. I would not make an exhaust like that anymore.

If I hold a 4 or 5 foot long pipe to my mouth and whistle or sing a note that slides from the highest to the lowest in my range there are likely to be a few that are noticibly louder. That behavior attracts "attention" when powered by mouth. If an engine were to have the opportunity to behave that way it would attract unwanted attention too.