Quite muffler that doesn't kill power...

MilesTugoh · Post by **MilesTugoh** » Sun Dec 30, 2007 3:39 pm

I am interested in creating a near zero loss exhaust system for my '47 Olds sedan, 500 ci, 1 7/8" four into one 3" collector 36" long, 2 1/2" pipe. 2.73 gear.

The resulting db level should be not just be legal quiet, I want it to be quiet quiet. This is not a race car, its a long distance cruiser with creature comforts.

My paper design approach has been to find muffler cases of maximum case volume, interior pipe size no less than In/Out size, highest flow rates (1100-1500 cfm), and install as many /side as space allows.

Is anyone aware of any 'rule of thumb' relating total muffler volume to engine displacement for maximum sound suppression ?

Thanks for your responses.

VMC · Post by **VMC** » Sun Dec 30, 2007 7:13 pm

randy331 wrote:
VMC wrote:I tested a pair of Walker # 17665 3" mufflers on my own 530+ HP 496 on the dyno. With a pair of 3' long collector extensions (trying to simulate under-car pipes on the dyno) they actually picked up 30 ft.lbs and 32 HP over open 2" headers and no collector extensions, and were surprisingly quiet until you really leaned on them.
Eric
It would be interesting to know how much power it would make with the 3' collector extensions, and no mufflers.

Randy

Randy;

I initially wanted to test just the collector extensions by themselves, but the dyno shop I use is located in a residential area. As with most other dyno cells, the exhaust normally runs from the collectors directly into the dyno cell mufflers, but there wasn't really enough room to install the colletor extensions and still attach them to the dyno cell mufflers; the only way to run the extensions was to open the bay doors of the dyno cell and run them out the back door of the dyno room. Even with the mufflers in place, I'm guessing the neighbors probably weren't all that amused.

At least now I know my particular combinations runs better with an exhaust system than w/o it.

Eric

Cougar5.0 · Post by **Cougar5.0** » Sun Dec 30, 2007 7:21 pm

I'm also using the 18" Magnaflows and they are fairly quiet.

hurstoldsracer · Post by **hurstoldsracer** » Sun Dec 30, 2007 9:11 pm

If you gain power by adding a muffler, your engine was inefficient to begin with. Any power gain you see by adding a muffler, was just part of the power that was lost by something else being wrong.

Forgive my ignorance, but what could be wrong that would cause you to pick up with a muffler? The same Monte SS that I described in my earlier post would run much better with mufflers than without, so would the Hurst Olds I raced after that. I am building a Camaro now and would like to avoid this problem again, even though I do not plan to ever take the mufflers off.
Mike

Dodge Freak · Post by **Dodge Freak** » Sun Dec 30, 2007 11:06 pm

If the motor has more power with a muffler than without, I always thought it was due too lean A/F ratio and a jet change would pick the power back up, but maybe theres more to it than that ??

crazyman · Post by **crazyman** » Mon Dec 31, 2007 12:18 am

Just thinking out loud, do you suppose it has something to do with the negative pressure waves bouncing back up to the valve at a different time due to muffler design, furthering the scavenging effect?

Post by **CamKing** » Mon Dec 31, 2007 12:36 am

hurstoldsracer wrote: Forgive my ignorance, but what could be wrong that would cause you to pick up with a muffler? The same Monte SS that I described in my earlier post would run much better with mufflers than without, so would the Hurst Olds I raced after that. I am building a Camaro now and would like to avoid this problem again, even though I do not plan to ever take the mufflers off.
Mike

It could be many things.
Too much exhaust duration for the exhaust port.
The wrong size header.
The wrong air/fuel mixture.
The wrong lobe centers.
The wrong length headers.

The fact is, if the restriction of the muffler picked your power up, you were down to begin with. The restriction from the mufler is band-aiding another problem.

KennyM · Post by **KennyM** » Mon Dec 31, 2007 1:45 am

An interesting support for the correct muffler tuneing, if you will, is the FORD trucks with the 4.6/5.4 gas motors.
Almost all who replace the OEM with some after market muffler or system looking for more power, noticably lose low end pulling power and maybe add some very small amount at top rpm.
The OEM mufflers are quite large and I say the factory has found out what will work and possibly makes them so they lengthen the total tract length, internally for the best overall comprimise.
I also see that Magnaflow comes the closest to the same power or sometimes even more.

n2omike · Post by **n2omike** » Mon Dec 31, 2007 9:19 am

If the muffler is NOT a restriction, and is simply acting as a collector extension... there is no reason to call foul for running better with mufflers.

Collector extensions can add significant power, especially in the midrange where most automatic cars launch. A friend with a 440 Valient picked up a solid tenth in the 60ft by bolting a set of Race Magnums to the header collectors.

If adding restriction to the exhaust picks up power, something is wrong. But adding mufflers... especially see-through ones with pipe the same size as the collector is a different ball game.

Good Luck!

Post by **CamKing** » Mon Dec 31, 2007 9:58 am

All mufflers are some form of restriction over a stright pipe.

FASTFATBOY · Post by **FASTFATBOY** » Mon Dec 31, 2007 10:54 am

CamKing wrote:All mufflers are some form of restriction over a stright pipe.

Even a muffler like a Maganflow or a Bullet?

David

VMC · Post by **VMC** » Mon Dec 31, 2007 12:04 pm

CamKing wrote:...The fact is, if the restriction of the muffler picked your power up, you were down to begin with. The restriction from the mufler is band-aiding another problem.

Agreed, assuming the engine wasn't built with the intent to have an exhaust system on it, but what if an engine was designed to run with mufflers in the first place?

I'd like your thoughts on the following, if I may ask;

The b.s.f.c. numbers on my 496 went down at peak HP with the extensions and mufflers in place, from .590 to .505, and went up slightly at peak tq, from .486 to .497. Along with the b.s.f.c. numbers leveling out, the engine picked up significant power everywhere across the board with the exhaust in place. I attributed this to the engine over-scavenging with an open exhaust. This was anticipated since I planned to run mufflers on it from the start and slightly over-cammed the exhaust side (+8° exh. duration @ .050) to compensate.

(It may be worth noting that I wound up having to go several jet sizes down on the carburetor from its factory specs as well)

Was I on the right track by slightly over-camming the exhaust side, or am I overlooking some other factors?

Eric

Post by **CamKing** » Mon Dec 31, 2007 1:52 pm

VMC wrote: I attributed this to the engine over-scavenging with an open exhaust. This was anticipated since I planned to run mufflers on it from the start and slightly over-cammed the exhaust side (+8° exh. duration @ .050) to compensate.

That is most likely the case.

As for you adding duration on the exhaust to help with running mufflers, it can help a little, but if you add too much duration, it can hurt the power a lot.

Just because you saw a power gain with the mufflers, doesn't mean your cam was helping gain back the power lost by the mufflers, the mufflers may have just been band-aiding an inefficient cam.

Say you have cam "A"(262-272), 406ci, 12:1, exh port flows 72% of int
It makes 600hp@7,000rpm, and 514lbs@4,900rpm.
You add your mufflers and the power goes up to 608hp, and 518lbs.

Now take cam "B"(262-266) in the same engine.
It makes 634hp@7,000rpm, and 532lbs@4,900rpm.
You add your mufflers and the power drops to 614hp, and 530lbs.

I'll take the cam that lost power with the mufflers.

Dodge Freak · Post by **Dodge Freak** » Mon Dec 31, 2007 2:19 pm

You guys are awesome !

I do recall hearing about how a cam with too much exhaust duration was like a built in EGR.

Post by **CamKing** » Mon Dec 31, 2007 2:31 pm

Dodge Freak wrote:You guys are awesome !

I do recall hearing about how a cam with too much exhaust duration was like a built in EGR.

Yep.
I found that out in the 80's when a lot of local short tracks started mandating mufflers.
I figured, I'd just take the cam that was working well without the mufflers, and increase the exhaust duration. All that did was kill the power and make the intake runners black.