Mufflers and hp

[David 23]

I wonder if anyone has objective, dyno proven data on various popular muffler/exhaust options and how they actually enhance or reduce power. I've heard a number of opinions, but they never seem to be consistent or backed up by data. I realize different engine configurations will cause different answers, but perhaps any specific data which would include the engine and exhaust configuration could be helpful to others. Anyone care to offer info?

[Reiver]

I've only tried the butt dyno and that is subjective.
Makers often provide information but rarely dyno charts.....this muffler makes 15 hp over stock etc.
They probably do but usually at WOT if more free flowing....I don't race my 911 daily so that is basically meaningless.
I have an '83 SC 930-10 Euro in fresh shape and I just tuned it up. I am in the process of putting EBS SCRS bumpers for and aft and wanted to test my muffler before cutting the rear unit.

I have SSI's and the motor is stock with a fresh top end...burns 8-10 ounces of oil in 3k miles between oil changes.


I ran the SSI's with no muffler (with ear plugs) on a route I normally can experiment with...rolling 5 mph full throttle stomp in 1st....and similar in all gears. It ran surprising well open with the headers only but the bottom end was soft to come on throttle thru mid rpm...high rpm was good. Thank God for ear plugs....and the countryside with no cops around.


I then ran a Dansk sport 2/1 w 70 mm exit pipe...that has a total area of exit at 5.93 inches.

Very nice....good throttle response thru mid and high range....I drove it about 100 miles in one day to get a feel....nice unit.


Following day a Dansk 2/2 peashooter w 50 mm twin exit pipes with a combined area in of 6.034.
Luckily the weather/temp was the same as the day prior low 70's w/ low humidity.


That muffler gave the best overall performance thru the rpm range from rolling 5 mph stomp (wheel spin) thru the top end.

Why, guessing the twin outs handle the pulse in a more uniform manner.....and they mirror the 2/1 in total area at the exit pipe.

This is just my non scientific experiment but who has the money or time to dyno numerous mufflers unless you are in the business and then you will only advertise your own in the best light possible.

That's as close as I can get.....and my 930-10 SC has a different cam/HP/comp ratio than the US models so is specific to that car.....that is the other issue. You'd need the same motor for all of the tests with the same conditions/same dyno etc.

[TimT]

This info is quite dated, but still relevant:

[mb911]

From an engineering standpoint how is that even possible for the triads? There is a huge brick wall in the flow path??


Not much beats stock for all around performance stock = 2 in 1 out..

[Reiver]

The chart is interesting but it shows, again, HP at WOT, where we race but do not drive.

I am more interested in torque not HP and when it comes on line. Exhaust tuning is interesting and like intake always a trade off for cars with non variable cams...an attempt to widen the sweet spot.

I agree about the 2/1 for the street....but found the Dansk 2/2 to be a tad more performance oriented (non scientific for sure) but...the exit area on the Dansk 2/2 is just about the mirror of the sport 2/1.

[Superman]

Originally Posted by mb911

From an engineering standpoint how is that even possible for the triads? There is a huge brick wall in the flow path??
..

Triads do well. I love mine. Disclosure: I know the guy who makes them. As far as the flow path goes, his build process involves some drilling....wink.

But....I love them mostly for the sound. I'd agree that WOT testing is mostly just relevant to racing. I'd also agree, heartily, that the best thing you can do for your engine is to bolt on a pair of SSIs. Read up (if you haven't already) on the physics of a "tuned" exhaust. SSIs really wake these motors up.

[Superman]

Also, in all fairness, 'mb911' makes a very popular exhaust. Good reviews. All in all, I'd recommend the Triad (1), the mb design which is somewhat similar (2) or the Bursch if you want a quieter, more throaty note.

[Bill Verburg]

Differently mufflers handle flow differently, the most efficient from a flow stand point is a straight pipe w/ a diameter that matches the flow volume and speed, next is a perforated straight pipe w/ the perforation walls outside the flow area, this is the design used in most glass packs, least efficient is a design w/ all sorts of bends, u-turns and baffles that adds turbulence to the flow.

[Trackrash]

There are a number of things to consider.

What motor are we talking about? All stock or modified?

Are you asking about just the muffler or the entire system?

If you have Bruce Anderson's Porsche 911 Performance Handbook there is a section with dyno graphs comparing different exhausts and mufflers.

A sport muffler, like the Dansk 2 in 1 out, will typically give about a 10 hp increase over the factory stock muffler.

According to Wayne in his How to Rebuild 911 motors book an SSI and sport muffler on an SC motor will give a 30-50 HP increase. (that is debatable)

The exhaust system should be configured to give the best performance in the desired RPM range as it is a part of the entire motor's tuning.

[chrismorse]

Given the range of camshaft personalities and cylinder head flow, my guess is that harmonics complicate muffler choice in the search for max power, best torque, most area under the torque curve, best sound, or lack of drone to the point of madness.
It might be possible to specify the most effective muffler for the range of engine displacements, purpose,(race, hot street, cruiser ) and sound, (if that is definable).
I remain optimistic,
chris

[Bill Verburg]

According to Wayne in his How to Rebuild 911 motors book an SSI and sport muffler on an SC motor will give a 30-50 HP increase. (that is debatable)

Not debatable, it's pure nonsense

[Bill Verburg]

Originally Posted by chrismorse

Given the range of camshaft personalities and cylinder head flow, my guess is that harmonics complicate muffler choice in the search for max power, best torque, most area under the torque curve, best sound, or lack of drone to the point of madness.
It might be possible to specify the most effective muffler for the range of engine displacements, purpose,(race, hot street, cruiser ) and sound, (if that is definable).
I remain optimistic,
chris

Mufflers aren't really that complicated

The complicated part is the header/collector, best there varies w/ displacement, cr, cam and usage

mufflers either flow well or not or somewhere in the middle. They don't contribute anything except noise attenuation, Their negative impact on performance can only be minimized.

When running open pipes on the other hand, the exit pipes can contribute significantly or not depending on design

[175K911]

Originally Posted by Bill Verburg

Not debatable, it's pure nonsense

Agreed. SSI and sport muffler on my ‘86 3.2 gave +18wheel hp at peak power on the Autothority dyno back in ‘88 after optimizing the software. Before software this exhaust caused a big flat spot at 3800-4000 rpm. One this engine. With this exhaust combination.

So many variables, everything from intake to tailpipe is a system that needs to be factored. Same sport muffler on the same ‘86 but with 1-5/8” Bursch headers gave +24 on the same dyno one day later, but at a higher rpm and gave less torque in the 2000-4000 range. Then software changes found some of the lost torque, same with having to rejet carbs with different exhausts on carb’d engines. Then C2 cams on the same engine and the same dyno one week later gave even more 3000-5000 rpm power with the headers but now the SSI’s would strangle the the engine over 5000 rpm.

So the real answer is “it depends”.

[175K911]

Oh, and on my current ‘86 with totally stock 190,000 mile engine and just 1-5/8 George headers plus factory sport muffler on a Dyno Dynamics dyno the car made 201.6 rear wheel hp in 2010, running the same Autothority prom I still had from 1988. Simply switching to one of Ben’s M&K 911R mufflers the next pull was 206 rwhp so his muffler made more peak power that the sport muffler.

[Jeff Alton]

Originally Posted by mb911

From an engineering standpoint how is that even possible for the triads? There is a huge brick wall in the flow path??


Not much beats stock for all around performance stock = 2 in 1 out..

I had one years ago, could not stand the incredible drone. And, the butt told me it was down on power vs the 2 in 2 to out Dansk....

There is not way a muffler change has the effect on HP that the posted chart shows...

[jamesjedi]

I think Wayne’s book refers to the 78-79 SC. 30 to 50 hp gain when cams/pistons and exhaust are changed.

I am at work, and do not have the book in front of me to reference.

[Reiver]

Originally Posted by jamesjedi

I think Wayne’s book refers to the 78-79 SC. 30 to 50 hp gain when cams/pistons and exhaust are changed.

I am at work, and do not have the book in front of me to reference.

Yes....it was more than simply adding the SSI's...he was referring to high compression JE pistons 9.8-1 a 964 cam and the SSI's.

I believe he mentioned somewhere, in one of his publications, a 15 hp gain using SSI's over the stock emissions systems that came on line in the later 70's....that would seem reasonable.

[mb911]

Originally Posted by Superman

Also, in all fairness, 'mb911' makes a very popular exhaust. Good reviews. All in all, I'd recommend the Triad (1), the mb design which is somewhat similar (2) or the Bursch if you want a quieter, more throaty note.

Superman I have nothing to do with M&k .. Haven't in 7 years.. I only make a few mufflers a year and they are carbon copies of the stock 2 in 1 out muffler .. I use them for my 914-6 guys.

I am speaking strictly as a bystander as I have no dog in the fight.. I just don't understand how the flow path can be a benefit. The dyno results just blow me away.. 2+2 doesn't add up on this.. I am speaking from someone that in the past has made thousands of exhaust and has real world first hand experience..

This also should be noted that Dave @triad is a great guy and I mean no ill will.

[lvporschepilot]

I just experienced this on a customer car with EFI. Previous muffler was a 2 in 2 out, I believe it was Dansk but can't be certain as it was old, but still in good shape. Swapped to M&K 2 in 1 out and the EFI system had to be adjusted at the top end as it was running about .3-.5 lean with the new muffler.

[jeffbottman]

My '86 Targa produced this dyno graph. Non-stock items are Steve Wong chip, M&K premuffler, M&K single output muffler. Dyno run at Drift Office LLC, Seattle area. About 210 RWHP max. Exhaust sounds great and does not drone.