Do muffs help flow?

Friend has car with dual muffs. Single cat/exhaust pipe. Typical newer car layout. His old muffs were rusted thru. Who can say what the insides looked like. Maybe gone? So he got new “turbo” muffs. He says they improve flow compared to stock muffs. He can “feel” the power improvement. What do you think of claim? Or different question. Do performance muffs improve flow compared to NO muffs?

Not enough information to say. Is this a Ford Fiesta or a Mustang? See my point?

BTW- there is a point of diminishing returns. The exhaust system must be designed to present a minimum amount of backpressure to prevent over-scavenging of the combustion chambers. On street cars, the exhaust system is usually a compromise between performance and noise suppression. Many cars can be improved with a less restrictive exhaust at the expense of increased noise. Some cars will see little to no benefit because the intake is so restricted, opening up the back end has no effect. There is no blanket statement that fits all situations.

BTW, the “feels more powerful” can often be attributed to a recent cash outlay rather than anything measurable.

What he ‘feels’ may also be noise, just like what you can get with a ‘high performance’ intake.

Both only make a difference at wide open throttle, and the difference may be next to zero.

97 caddy Sts. 300hp, 6k redline? Been told intake is almost zero restriction. There is almost nothing that can be done to find any extra power on the car. I don’t see how any internal design of muffs can improve or smooth out the flow of exhaust.

I think you’re right. The intake/exhaust system is like a long chain, doubtful that the mufflers would be the ‘weakest link’.

The old saying goes “your butt dyno is full of crap.” i.e. you cannot tell just from the seat of your pants if there’s been an improvement just from something small like a muffler. You can only tell by measuring, which requires an actual dyno.

Sometimes the sound of the car can seem like more or less power. Blown out mufflers can make the car sound like it has less power. Fully functioning mufflers can make you feel more power at less volume. It’s a sound theory.

Well, if a muffler is holding the sound down, it is holding the power down also.

30 years ago a tuned exhaust could make a huge difference in certain vehicles. But with computer controlled systems it’s highly unlikely that changing the mufflers will make one bit of difference.

I can attest that it is strictly a sensation, but a sensation that feels real. I just put a new OEM spec muffler on our Honda. The intake pipe on the muffler developed a good sized hole so the exhaust got quite loud. As soon as that happened, the car felt like it had less power. The truth is that I was much gentler on the throttle so as to not make a lot of noise.

Don’t get me wrong here, I do like the rumble of a nice tuned exhaust but a hole in the pipe is not the same sound and I don’t care for that sound. Anyway, new muffler installed, exhaust is silent and the car actually feels more powerful, but I know its not.

Often fiddling with the tuning of the exhaust or intake just adds another kink or ripple to the torque curve.
So maybe the torque is increased a little over a narrow range of speeds.
So a wishful driver feels that little kick and thinks he’s got something going.
He doesn’t notice the dip right next to the peak.

A similar thing happens with the boy-racer who uses exhaust piping too large in diameter for a street car.
The torque and hp is increased up near the redline where race cars live, but the exhaust velocity is too low at lower rpm’s and flexibility suffers on the public roads.

I’ve read a number of tests of (EXPENSIVE) replacement systems on motorcycles, many make next to 0 difference. But they’re LOUD!

@texases Heh. I have a CRX and an MR2. Both boy-racer type cars despite the fact that I haven’t been that young in way too long. Stock muffler replacements are absurdly expensive, but it’s hard to find an aftermarket one that doesn’t sound like angry bumblebee farts. I finally found one - the Dynomax Super Turbo. It’s not a turbo, and it’s not super, and it certainly doesn’t make the cars max the dyno, but it’s nice and quiet, just the way I like it.

I think in a lot of cars the dual exhaust pipes are more for show than for performance. It’s like those short chrome tail-pipe ends you can buy to put on the end of the exhaust pipe. Just for show. On some cars, I wouldn’t be surprised if the configuration, if you looked underneath, is for the most part a single pipe/cat/muffler path, and then after the muffler the pipe is divided so to show to the world two pipes coming out the rear of the car.

Still, in max acceleration mode, the pedal to the metal, the engine is sucking in as much air as fast as it possibly can, and pushing out as much exhaust gas as fast as it possibly can. It’s like a long tube, max flow rate all around. The effective flow rate from one end to the other determines the engine power. Any part in the flow chain, from the air filter through to the muffler, any part that limits the flow rate will reduce engine performance. If the exhaust flow through a single muffler is the most limiting factor in the chain, then it stands to reason having two exhaust pipes and two mufflers would shift the limiting flow device somewhere upstream, and could improve performance.

But by how much? You still have the cat honeycomb in the exhaust path, and the cat honeycomb restricts airflow. So you may well have to double up on the cats too, to see much of an improvement in dual exhaust systems. The other factor to consider is that newer cars have O2 sensors at various points in the exhaust path. The ECM reads these sensors, and uses an algorithm based on the engine and exhaust design, to determine how much gas to inject via the injectors to achieve the best air/fuel mixture. Changing the exhaust path from the way the car was originally designed could confuse the ECM and might actually reduce the overall engine performance unless a corresponding compensation was made to the ECM software.

The same thing – a confusion of the ECM resulting in poor engine performance – can happen if you get a hole in your exhaust system. Outside air can enter the exhaust stream through the hole. The ECM assumes the only O2 getting into the exhaust stream is coming from the combustion chambers, not from outside air.

I wonder about the amount of back pressure needed for optimum performance, as designed. So you reduce back pressure by glasspacs, does that mean improved performance?

Thats what I have been telling my Flowmaster buddy,aside from scavenging you are just trying to reduce the pumping losses.
Now tell me truly,how much do headers help on a stock engine with dececent exhaust system to start with?-Kevin

I think it’s probably a placebo effect. I used to think my car ran smoother after an oil change, but the logical part of my brain knew better.

My vote is for placebo. In the past I’ve used glasspacks, turbo mufflers, and so on and never found a car to run any faster or gain any fuel mileage. It sounded cool though; or so I thought for a brief period of time.

I don’t watch many car shows on TV anymore as they’re all pretty much garbage infomercials. The show Gearz seemed to be one of the better ones at one time but a few weeks ago they showed a cat back muffler and tailpipe being installed on a pickup and the claim was that modification alone gained 38 horsepower and 50 Ft. Lbs of torque. I’m not buying that for a minute.

@OK, on one of those infomercial TV shows they showed a lot of impressive gains with a complete tuneup new cat back system and headers,big bucks indeed,What they didnt show was,what would give you the most bang for the buck(tuneup,replacing stopped up cat,etc) from there on out that show didnt have the same appeal for me-Kevin

So, generally speaking, a less restrictive muffler MAY improve exhaust flow and provide marginal power increase. But in MY case. What does a 14yr old factory GM Sts muff look like inside? Has it collapsed to the point of impeding flow? Is it gutted and have no flow restriction? Does an empty muffler shell actually impede the flow of exhaust gas due to odd, square internal shape? So will a new turbo muffler actually flow better than a gutted oem muff? Who can say