I have read that good mufflers can increase torque at lower revs. David Vizard disagrees. He is a prolific automotive writer with, I understand, extensive experience building engines and racing cars in the British racing scene, and aerospace engineering experience. I guess he does a lot of consulting work, because he seems to run his own dyno. He says that mufflers only reduce engine output, regardless of the engine to which they are attached. Any opinions?

 

The way I see it and I'm no expert is that the exhaust system is tuned for the car and any changes may affect the outcome. For instance, the stock LT1 exhaust is pretty damn good. I'm running in the 12's with the stock exhaust on my '93.

On my '95 with the stock exhaust I ran 13.0. On that car I removed the mufflers and only realized a gain of .08 in the 1/4 but my mph was reduced by 1.5 mph. So that indicates a power loss.

I out a Corsa catback system on and got the 1.5 mph back, so something is said about having mufflers, or at least the proper one.

 

As an aside, each engine has a certain amount of torque/horsepower it can produce. Adding/deleting mufflers or other items in the system may allow the engine to make closer to its potential horsepower and torque. However, the potential of the engine might only be reached through an exact combination of things like exhaust, intake, plugs and wires, timing, etc.

To say that such and such "added" 10 horsepower, as many people do, is really an incorrect statement. You didn't add it, it was already there. On a particular engine, removing the mufflers might remove a restriction that allows the engine to achieve more of its potential. On another engine, removing the mufflers might take away a critical part of the system that the engine was tuned to operate with. In that case, you would lose horsepower and/or torque.

On my LT1 when I removed the mufflers, I felt like I lost some sub-3k rpm torque. Don't have any dyno numbers to prove it, but I could feel it. Maybe it was actually just a change in throttle response. I don't know, but something was different. Putting mufflers back on restored the low-end zip.

So obviously on my particular engine, the thing is designed to work with some backpressure. May be different for someone else's engine. The only way to really know for sure is to tune the thing on a dyno.

Sorry for rambling there.

 

ANY restriction in the exhaust has an adverse effect on performance. This is why rails, funny cars, nascars, etc.. do not restrict their exhaust. If mufflers had ANY posisitve effect, don't you think that all of the abot cars woudl use some type of them? :yesnod:

 

Go ahead and run your car with no exhaust and see what happens, you'll more than likely slow down.

 

These cars need a certain amount of backpressure to run optimally. I think thats why the muffler eliminators sometimes cause a power loss.

Really it all comes down to the individual motor and what its power band is. L98 needs a little back pressure, LT1/4 also. A motor like the ZR1 which makes less down low torque and more high rpm power can benefit from no back pressure, but it will be at the expense of bottom end torque.

 

I had my mufflers on my 85 removed 3 years ago and the day I did I noticed an improvement right away. I don't have any proof but the feel of the car. And it feels much better now without them. Mine just has tips on it. I'm not saying none of them need back pressure. But mine seems to like it without the mufflers. I do still have some back pressure from the cat.


[Modified by Davidsvette85, 2:21 PM 11/23/2003]


[Modified by Davidsvette85, 2:22 PM 11/23/2003]

 

I have run my car with no exhaust using an exhaust bypass. It does not slow down. The requirement of back pressure is a myth. You have valves in your heads that stop flow in sync with the command of the cam lobe. When the valve is closed, back pressure has no effect. Now if your exhaust valve springs are weak, then back pressure can assist the closing of the valve.
The game of horse power is majority based on unrestricting the flow of air and fuel. Restricting either results in less performance... Good headers are "tuned" to actually help "pull" exhaust from the motor. This is done because back pressure and restriction are not performance enhancers. :lurk:


[Modified by c4power, 9:23 AM 11/23/2003]

 

Thanks to everyone who replied. I knew I would generate some conversation with this posting. I am inclined to think that mufflers reduce engine output, but I'm not sure. Perhaps any gains that people measure or feel when their cars have mufflers can be attributed to the stock ECM, which is programmed with mufflers in mind. I'm not sure about that, either. I wish I could somehow get David Vizard to weigh in on this discussion.

 

Totally agree with Mojo. In days past, my Nova actually picked up a tenth with mufflers and an air cleaner vs. open headers and no air cleaner. On top of that, look at the latest header collector design in Pro Stock. While still mufflerless, they are engineering in small reductions in collector diameter to help torque and hp numbers.

Comparing a top fuel car to a street/strip car is not entirely apples to apples. When done properly, a tuned exhaust will help a car unless it is simply designed to run at insane RPMs.

 

I have hundreds of timeslips to back up my findings. I'm also talking on a stock system. Start modifying and it's a different story.