Aftermarket muffers and performance/efficiency

[Johnny248]

I know there is actually more involved in exhaust design than just a pipe to redirect exhaust out from under the car, however I'd like to see what peoples opinions are on replacing an OEM muffler with a straight through design muffler.

There are a lot of vechiles today that appear to have a good flowing exhaust sytem with nice smooth bends and decent diameter pipe. However, most seem to use some sort of baffled style muffler.

What effects if any would there be to replace just the muffler with a straigh through design muffler such as a magnaflow? I know it will be louder, but are there any real time gains in engine power or increased fuel economy for have less restriction on the exhaust fumes in todays vehciles?

 

[SteveSRT8]

This is very vehicle specific. But most factory systems are very well engineered and make excellent power without much noise.

Beware as many cars these days react poorly to lowered back pressure and or velocity changes. You may require tuning to develop any additional power at all, and the gains are always very small.

As an example, on my car a cat back with drastically better flow numbers results in a very slight gain in HP at the upper rev range and a huge drop in torque at the bottom! Generally the car is quite a bit slower than a bone stocker!

 

[dparm]

A few percent, perhaps. And that's only at WOT at redline.

Without a proper exhaust SYSTEM (aka headers, cat converters, tubing, etc), the muffler alone will make no difference except adding noise. Loud != fast.

 

[pcfxer]

The muffler is a bottleneck in my car (and most other Nissan/Infinitis).

 

[Malo83]

Anything is better than a stock muffler

 

[user52165]

Originally Posted By: Malo83
Anything is better than a stock muffler

As mentioned, it is very vehicle specific. You cannot make that generalization without mentioning what car.

 

[Cujet]

As mentioned above.

However, my guess is that you already know this.

The early Mazda Miata gains nearly nothing by installing a header and exhaust, with free flow (or no) catalytic. Is it measurable? Yes, is it a waste of money? Yes.

However, take that same miata and add a few other modifications, now the output increases dramatically. It's not unusual to see 90HP in stock form. 93 with $1000 worth of exhaust mods. Add some mild cams, improved intake manifold, larger throttle body and higher compression pistons and now the RWHP jumps to the 150HP range. That's 60% more real world HP.

 

[440Magnum]

Originally Posted By: Cujet
As mentioned above.

However, my guess is that you already know this.

The early Mazda Miata gains nearly nothing by installing a header and exhaust, with free flow (or no) catalytic. Is it measurable? Yes, is it a waste of money? Yes.

However, take that same miata and add a few other modifications, now the output increases dramatically. It's not unusual to see 90HP in stock form. 93 with $1000 worth of exhaust mods. Add some mild cams, improved intake manifold, larger throttle body and higher compression pistons and now the RWHP jumps to the 150HP range. That's 60% more real world HP.


Well of course. The camshaft (and nowadays the PCM tune) are the keys to any engine's performance characteristics. Unless the stock exhaust or intake system is just STUPID restrictive (and there really aren't many cases of that since the 80s), neither is going to be the limiting factor. Cold air intakes and cat-back exhausts are largely placebos, and even when they do aid performance measurably the actual bang for buck is small. Granted, they often sound nice, but that's about it most of the time.

 

[SteveSRT8]

Originally Posted By: Cujet
As mentioned above.

However, my guess is that you already know this.

The early Mazda Miata gains nearly nothing by installing a header and exhaust, with free flow (or no) catalytic. Is it measurable? Yes, is it a waste of money? Yes.

However, take that same miata and add a few other modifications, now the output increases dramatically. It's not unusual to see 90HP in stock form. 93 with $1000 worth of exhaust mods. Add some mild cams, improved intake manifold, larger throttle body and higher compression pistons and now the RWHP jumps to the 150HP range. That's 60% more real world HP.


Excellent point.

If you use my car as an example, adding a very low restriction cat back (my car already has a nice factory shorty header and 2.875 tubing) moves the torque curve up from an already high 4800 rpm peak.

While you technically add peak hp (few for the dollars) you are left with a car that is noticeably slower off the line than a stocker!

Since I like quiet my stock pipes are fine. They bark when you get on it. I learned long ago that people will foolishly underestimate a car that is quiet.

Can you say "sleeper"?

 

[artificialist]

When I had a fully built cat back for my 2003 Saturn ION, it made more power across the entire band.

Many cars benefit from performance cat-backs, it depends on how the OE system was built.

 

[ahoier]

Originally Posted By: dparm
Without a proper exhaust SYSTEM (aka headers, cat converters, tubing, etc), the muffler alone will make no difference except adding noise. Loud != fast.
Yep, what I've been reading too.....you typically can't just change the muffler/exhaust and expect to get HP/MPG gains.....the real benefits come when you change/adapt the whole system.

 

[dwendt44]

My vehicle has two cats a resonator and a large baffle type muffler. On top of that, it also has a odd shaped and restrictive "Y" pipe.
It's a small V-6 but I'm sure a better designed exhaust system would gain some improvement all around.

It is stainless steal however, and will likely last well past 100,000 miles.

 

[dwcopple]

Originally Posted By: dwendt44
I'm sure a better designed exhaust system would gain some improvement all around.

I'm sure it would too...

 

[dailydriver]

Originally Posted By: dparm
A few percent, perhaps. And that's only at WOT at redline.

Without a proper exhaust SYSTEM (aka headers, cat converters, tubing, etc)


In some states/locales you CANNOT get away with long tube headers, even with OEM style 400 cell, ceramic matrix cats attached to the ends of them, let alone lower restriction (but much easier clogged/killed with a performance tune) 200 cell metal matrix catcons!!!

"Shorties" (short tube headers) are generally NOT considered worth the coin/bother, since they usually only give ~5whp over stock manifolds (if you are really lucky), even though they bolt right up to the OEM/OEM style 400 cell cats.
They DO save a few pounds of fat off of the front end, over heavy cast iron exhaust manifolds if that is standard on one's car, however.

 

[artificialist]

Yeah, the reason long-tube headers aren't legal without a special certification is because they dissipate more heat before it reaches the cat, meaning the cat needs more time in order to be effective. The heat dissipation is also why long tube headers are not as effective as they look when installed on turbo engines.

One suggestion I have read is to keep the iron manifolds, but port them well.

 

[rslifkin]

I agree on headers having limited benefit on a lot of engines. However, on some with poorly designed manifolds, there would be large gains. On my Jeep, even with the heads, cam, etc, from what I've modeled in engine analyzer, a good set of longtubes would give me about 10 hp and 5-10 ft. lbs. over the stock manifolds with a good y pipe. IOW, considering the headers would have to be totally custom to fit in the Jeep, not worth it.

However, the cat warmup thing is vehicle dependent. On the Jeep, the cat is behind the y-pipe both in stock form, and with my re-done setup, so longtubes wouldn't put it any further down the system (it already takes a while to warm the cat). If anything, for me, longtubes would warm it up faster, as they could be wrapped or ceramic coated to retain more heat, while the y-pipe isn't.

 

[SteveSRT8]

Agreed, very vehicle specific info. I'll bet the 5.9 uses very rich startup programming to light the cat up quickly.

Got a large displacement engine? Expect bigger gains from a well designed header over an iron 'log' style manifold. Modern engines will generally need some tuning to get the best gains.

And Chrysler knows how to make a good shorty, wrap it in sheet metal to retain heat (and noise). 5.7 owners gain 20 hp with these installed off a 6.1. No rise in underhood temps!

Seriously, most of the smaller motored economy type cars will get virtually nothing from exhaust work. If there was an mpg in there somwhere you can bet the mfgr would have found it. A leading tuner admitted to me that 5 or 6 percent was the most he had ever seen in gains on later model 4 bangers.

 

[dailydriver]

Originally Posted By: rslifkin
I agree on headers having limited benefit on a lot of engines. However, on some with poorly designed manifolds, there would be large gains. On my Jeep, even with the heads, cam, etc, from what I've modeled in engine analyzer, a good set of longtubes would give me about 10 hp and 5-10 ft. lbs. over the stock manifolds with a good y pipe. IOW, considering the headers would have to be totally custom to fit in the Jeep, not worth it.

However, the cat warmup thing is vehicle dependent. On the Jeep, the cat is behind the y-pipe both in stock form, and with my re-done setup, so longtubes wouldn't put it any further down the system (it already takes a while to warm the cat). If anything, for me, longtubes would warm it up faster, as they could be wrapped or ceramic coated to retain more heat, while the y-pipe isn't.


I was saying that CARB/DOT/EPA legal, aftermarket, 'shortie' headers give little to nothing (as far as power gains) over stock iron manifolds.

Now LONGTUBES over the stock pigs is a whole 'nother story!!

On LS1 4th gen f bodies, some have gained as much as 40hp to the wheels with just longtubes and a good tune!

If my catcons were as far back as yours are in the system, I would already have had longtubes on the car for 11 years!!!

 

[dailydriver]

Originally Posted By: SteveSRT8
Agreed, very vehicle specific info. I'll bet the 5.9 uses very rich startup programming to light the cat up quickly.


Does the catcons 'lighting off' much quicker also help save them/ensure their longevity, besides putting out less emissions during open loop operation??

In other words, if you had a hand held programmer (like a Diablo Sport Predator), and it gives you the tuning option to control the COT (catalyst operating temp, or light off temp), would setting it higher or lower help the longevity of the catcons, given that it is dumping more raw fuel into them if one sets it lower (than let's say 400*F)???

 

[SteveSRT8]

Actually the majority of owners in my community have nothing but problems with anything other than stock cats. They constantly throw codes, collapse internally, etc.

I can't really say that I know the answer to your question. On my tuner that is not an option. I can adjust the mixture and spark timing but only within narrow ranges.

I've seen cats overheat from a misfire, so it would seem richer mixture=hotter cat, but yet many cars have a "cat protect" mode involving a super rich mix that actually cools them under load.