Sizing up a straight through muffler

[Slanter]

This was in response to the "What car are you considering fixing up?" thread, but I thought it's enough of a tangent that I ought to spin off this discussion into its own thread.

There are so many types of performance mufflers on the market, it staggers the imagination. Trying to pick which one can be pretty confusing. Some things I can't help you with. Trying to evaluate how a muffler will sound is pretty tricky. The rest of the engine has a huge effect on the exhaust tone, so a muffler that produces a deep rumble on a V8 may yeild a harsh, obnoxious buzz on a naturally aspirated inline four and make a turbochargered inline six sound like a jet engine. The best you can do is guess based on how other cars you've personally heard with similar engines sound with different mufflers.

Likewise, trying to evaluate how well a chambered muffler will perform by looking at it is virtually impossible. The best thing to do here is go by dyno reports about engines similar to yours, if you can find them. Sometimes you can get flow data and go with David Vizard's rule of thumb that a muffler should flow 2.2 CFM for every horsepower you'd expect to make without the muffler (Using two mufflers in a dual setup, naturally, doubles the CFM).

Luckily, straight through mufflers are both common and pretty easy to evaluate. The first thing to do is look through it. You want a tube that is the same diameter as the inlet and outlet, all the way through. One "performance" muffler made by a company that shall remain nameless actually had the pipe inside neck down to less than an inch in diameter. The store clerk pointed out that its carbon fiber construction made it lightweight... big deal if you've got to run four mufflers if your engine makes decent power. And big expense. Also, for best performance the muffler should not have objects sticking out into the tube - just holes letting the gas expand into the packing. Of course, this will also be pretty loud - just listen to a car with a Thrush Magnum Glasspack! The Thrush is a prime example of a straight through muffler with very little restriction.

The other thing to consider is durability. A cheap muffler (again, the Thrush comes to mind) will be made of steel with some sort of coating on it and packed with fiberglass. Both will deteriorate over time. Some glasspacks have been known to lose all their packing within a year. Stainless steel cases can hold up better, and packing a muffler with stainless steel wool or high tempterature ceramic means longer life for the packing.

As for the tip design, very few of the tips on the market look like they will improve flow, and even the few that might (long conical designs) probably will have no measurable effect on performance. A handful of exhaust tips (some of the "Chevy Bow Tie" ones are perhaps the worst offenders) actually create exhaust restriction. Not what you want, usually.

[Robert-The-Rambler]

This was in response to the "What car are you considering fixing up?" thread, but I thought it's enough of a tangent that I ought to spin off this discussion into its own thread.

There are so many types of performance mufflers on the market, it staggers the imagination. Trying to pick which one can be pretty confusing. Some things I can't help you with. Trying to evaluate how a muffler will sound is pretty tricky. The rest of the engine has a huge effect on the exhaust tone, so a muffler that produces a deep rumble on a V8 may yeild a harsh, obnoxious buzz on a naturally aspirated inline four and make a turbochargers inline six sound like a jet engine. The best you can do is guess based on how other cars you've personally heard with similar engines sound with different mufflers.

Likewise, trying to evaluate how well a chambered muffler will perform by looking at it is virtually impossible. The best thing to do here is go by dyno reports about engines similar to yours, if you can find them. Sometimes you can get flow data and go with David Vizard's rule of thumb that a muffler should flow 2.2 CFM for every horsepower you'd expect to make without the muffler (Using two mufflers in a dual setup, naturally, doubles the CFM).

Luckily, straight through mufflers are both common and pretty easy to evaluate. The first thing to do is look through it. You want a tube that is the same diameter as the inlet and outlet, all the way through. One "performance" muffler made by a company that shall remain nameless actually had the pipe inside neck down to less than an inch in diameter. The store clerk pointed out that its carbon fiber construction made it lightweight... big deal if you've got to run four mufflers if your engine makes decent power. And big expense. Also, for best performance the muffler should not have objects sticking out into the tube - just holes letting the gas expand into the packing. Of course, this will also be pretty loud - just listen to a car with a Thrush Magnum Glasspack! The Thrush is a prime example of a straight through muffler with very little restriction.

The other thing to consider is durability. A cheap muffler (again, the Thrush comes to mind) will be made of steel with some sort of coating on it and packed with fiberglass. Both will deteriorate over time. Some glasspacks have been known to lose all their packing within a year. Stainless steel cases can hold up better, and packing a muffler with stainless steel wool or high tempterature ceramic means longer life for the packing.

As for the tip design, very few of the tips on the market look like they will improve flow, and even the few that might (long conical designs) probably will have no measurable effect on performance. A handful of exhaust tips (some of the "Chevy Bow Tie" ones are perhaps the worst offenders) actually create exhaust restriction. Not what you want, usually.

Again thanks for the detailed explanation.

[Robert-The-Rambler]

I looked underneath the car and realized dual exhaust is not a smart option because of all the twists and winds necessary to navigate all the crap under there. But anyway I got a muffler with dual 2 1/4" tips that are perfectly round and it sounds phenominal. I get looks all the time. I don't know the model number but I am impressed. It really gives the car a higher end sound. It is deep at low rpms and screams at high rpms. I love it!!!!! I got hosed on the price but the thing was installed for $289 in under an hour paying by credit card. It would have been $250 cash. It doesn't have that famous riceburner buzz. It sounds like real power.

[Slanter]

Muffler questions seem to be common enough that maybe I ought to make a sticky out of this thread.

[-JJ-]

So how about non-straight-through mufflers? Specifically, does the 2.2CFM/hp rule still apply, and does an H-pipe/crossover (versus true dual) affect muffler selection/pipe diameter?

[Slanter]

So how about non-straight-through mufflers? Specifically, does the 2.2CFM/hp rule still apply, and does an H-pipe/crossover (versus true dual) affect muffler selection/pipe diameter?

Yes, the rule for sizing a muffler applies to any muffler type. The crossovers generally improve performance, and I've seen a few dyno tests that suggest the new X-pipes are superior to the H-pipes. However, I doubt they would warrent a smaller muffler or smaller pipes. I have not seen a dyno test that compared both pipe diameter and crossovers, though.

[-JJ-]

Yes, the rule for sizing a muffler applies to any muffler type. The crossovers generally improve performance, and I've seen a few dyno tests that suggest the new X-pipes are superior to the H-pipes. However, I doubt they would warrent a smaller muffler or smaller pipes. I have not seen a dyno test that compared both pipe diameter and crossovers, though.

Hmm.. that's rather what I figured, about flow. You've piqued my interest, though... now I'm going to have to investigate an X-connect as well. Crap. Oh well, just one more thing to add to the List.

Thanks Slanter, good stuff.

[BlueZQ8]

I just thought I'd add that when choosing an exhaust system, you don't wat to go too big either. If you do go with a setup that is too large, you may actually lose power and torque, because a certain amount of back pressure is required.

[Slanter]

Actually, it's not the backpressure that's required, although too large a diameter can apparently hurt power. Some high revving engines may give up a bit of low RPM torque if your reduce back pressure, but this is not the case for all engines.

I have seen a few accounts about oversized exhausts losing power, but many of the theories I've seen as to why this happened actually defy the laws of physics. The nearest I can tell is that a pipe that's the right diameter will keep a steady flow through it, but a pipe that's too large will sometimes cause the air to stop in between cylinder firings and make the exhaust hit a "wall of air" or even have pulses flow momentarily backwards. In either case, the problem is too much effective back pressure rather than too little.

[Radd2]

Hey. Ive always heard pretty good things about flowmaster, and ive read about their mufflers. They seem to be at the top of the industry. Any opinions on quality, ease of installation, etc.?

[CVStroker]

Personally, the best exhaust I'v ever heard was without a muffler. But it wasn't running straight pipes. It was a GM small block 350 V8 running 3" pipes from the headers to catalytic converters from an early 90s GMc Sierra, then 3" exhaust from there back. It gave the most orgasmic rumble at idle and low rpms, and a powerful growl at high rpms. Awesome thing is, the sheer size of the CCs muffled the exhaust enough that it was legal (or at least close enough to legal to not cause any problems).

Sorry to bring it back from the dead, but it's 4:45 am and I'm bored out of my mind

[Derek_Thompson24]

I just wanted to add..

If anyone is buying mufflers based on their CFM ranges such as 1050 CFM.. those advertisements are nothing but false to anybody. Your engine is as good as its worst part. If your exhaust is putting out 550 CFM with straight pipes ur not going to just boost up to 1050 CFM with the new muffler.

[silvia]

I saw that someone was thinking about X pipes. These have a slight advantage over H pipes in the fact that the junction is much bigger, allowing smooth flow thruout the exaust system while still enabiling the two sides of the engine to maintain equil back pressure. If you are building your own exaust system, these are you best choice. However, if you system is already built with an H pipe and you are not clawing to find more power, its not worth it to change it out.

[toyotaridingdude]

Wow, this is informative stuff. Thanks for sharing it.



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[dodgeballer]

I'm a bit late to the game, but thanks for the info!

[mikebalint]

I really like all the ideas you guys have. Before I bought my exhaust system for my Lincoln Aviator, I looked up some different articles in magazines that compaired different companies. They were comparing the systems on muscle cars, but I thought the comparasin would stand. They compared the performance changes from stock for Flowmaster, Magnaflow, and Borla. I was shocked to see that the Flowmaster actually lost 1 horsepower from the stock system, while the Magnaflow and Borola gained power (like you want). They gained about the same, but the Magnaflow is more affordable and is made of stainless steel with a lifetime warrantee, so I picked that one. I also researched and got a good deal at www.muscleexhaust.com . They have low prices with free shipping and also threw in a K&N air filter for free. You just have to ask when you buy your system. They also sell the K&N airkits, which get really good horsepower additions and better gas milage, and Superchips to tune the cars. They didn't make an airkit for the Aviator, but I bought one and a Superchip for my Mustang and got AMAZING results. www.muscleexhaust.com seemed the best to buy online to me. You get a better deal buying online than through a shop that ups their prices. I could even install the exhaust system myself, so I didn't have to pay anyone to do it. Just uses basic hand tools.

[austinkli]

Personally, the best exhaust I'v ever heard was without a muffler. But it wasn't running straight pipes. It was a GM small block 350 V8 running 3" pipes from the headers to catalytic converters from an early 90s GMc Sierra, then 3" exhaust from there back. It gave the most orgasmic rumble at idle and low rpms, and a powerful growl at high rpms. Awesome thing is, the sheer size of the CCs muffled the exhaust enough that it was legal (or at least close enough to legal to not cause any problems).

Sorry to bring it back from the dead, but it's 4:45 am and I'm bored out of my mind

While this is usually true for any car, including my 84 celica, it doesn't really give much of a power boost. I ran straight pipes on my celica, and the sound was amazing. As I downshifted around the corner of my neighborhood every night, you couldn't help but wonder, is that a ferrari or that celica at the end of the street. Unfortunately to say, while cheaper than a good muffler, it's just not as effective.

[zacknolden]

Is it true that if you hear any exhaust noise, the muffler or pipes are probably leaking and repairs are needed? Thanks
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[Jichino]

Most sizing rules for mufflers applies to all mufflers regardless of the car model. The crossovers does infact improve performance, but i doubt most people would settle for the slight improvement in performance and have a smaller muffler.

[v2c4]

thank's for tips

[samrawet]

THANKS FOR SEARING THAT INFORMATION

[lamb2]

the explanation which has been given is very exploratory in nature and very easy to understand...thanks for this article dear......

[michl87]

a very nice article...indeed ....i must say it is very knowledge enhancing thing written there....very nice...

[nally]

if your engine makes decent power. And big expense. Also, for best performance the muffler should not have objects sticking out into the tube - just holes letting the gas expand into the packing. Of course, this will also be pretty loud - just listen to a car with a Thrush Magnum Glasspack! The Thrush is a prime example of a straight through muffler with very little restriction











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[steven444]

thanks for the informative post