Supercharger exhaust Q & A's

**chikinhed** · 03-23-2008, 01:16 AM

I am trying to get the most out of my stage 2+ supercharger kit. Because of a low Load% reading I checked my stock exhaust for back pressure and found it to have 11 psi of back pressure near redline. To remedy this I thought a simple bolt on AA track pipe would fix this ..... it only brought it down to 9 psi of back pressure which is still WAY too high. So then I decided to use the front part of the AA track pipe and make a 3" mandrel bend exhaust with a high flow cat and long Magnaflow straight through muffler ..... that gave me 9 psi back pressure and a very loud sound. I then replaced the cat with an ultra quiet straight through resonator ..... that gave me 2.5 psi back pressure and about the same sound. Next I will be trying a Moroso Spiral Flow Muffler. Just as a quick test I put it on the outlet of the Magnaflow muffler and it was so quiet. So quiet in fact that I expect the back pressure to increase. I will respond back with the results.

I would like to know what all the other supercharged cars are using for exhausts and if any of you have found the secret combo that gives low back pressure and minimal sound volume ( I don't like loud cars any more).

**Shuasha** · 03-23-2008, 01:52 AM

Originally Posted by chikinhed

I am trying to get the most out of my stage 2+ supercharger kit. Because of a low Load% reading I checked my stock exhaust for back pressure and found it to have 11 psi of back pressure near redline. To remedy this I thought a simple bolt on AA track pipe would fix this ..... it only brought it down to 9 psi of back pressure which is still WAY too high. So then I decided to use the front part of the AA track pipe and make a 3" mandrel bend exhaust with a high flow cat and long Magnaflow straight through muffler ..... that gave me 9 psi back pressure and a very loud sound. I then replaced the cat with an ultra quiet straight through resonator ..... that gave me 2.5 psi back pressure and about the same sound. Next I will be trying a Moroso Spiral Flow Muffler. Just as a quick test I put it on the outlet of the Magnaflow muffler and it was so quiet. So quiet in fact that I expect the back pressure to increase. I will respond back with the results.

I would like to know what all the other supercharged cars are using for exhausts and if any of you have found the secret combo that gives low back pressure and minimal sound volume ( I don't like loud cars any more).

I'm very interested in this myself. I'm doing an E34 532 SC exhaust pretty soon.

**WK446** · 03-23-2008, 02:28 AM

chikinhed: I'm interested in this as well. BTW, how are you intending on passing Aircare?

**Shuasha** · 03-23-2008, 02:35 AM

What are you using to measure backpressure?

**chikinhed** · 03-24-2008, 01:17 AM

I removed the wide band O2 sensor for my AEM gauge from the exhaust bung, installed a fitting that I made, hooked up to a hose that I ran in to the car to a calibrated pressure gauge.

**chikinhed** · 03-25-2008, 05:20 AM

Tonight I installed the 3" Moroso Spiral Flow muffler in my exhaust ..... Back pressure was back up to 9 psi. so out it came. It was quiet, but obviously for a reason. I would not recommend this muffler because of the back pressure it adds. On goes my quest for quiet power.

Over the past week since I had reduced my back pressure down to 2.5 psi, I have more and smoother power between 6000 and 7000 rpm. My long term fuel trims have gone leaner as well.

**WK446** · 03-25-2008, 11:55 AM

chikinhed: Check your e-mail or PM me another contact e-mail please.

**///M3 CRAZY** · 03-25-2008, 11:58 AM

i had the track pipe and a no name aftermarket exhaust (straight through design)...

**chikinhed** · 03-25-2008, 12:18 PM

I don't want to stay with the AA track pipe because with just the track pipe and no muffler attached to the back of it I was getting 4.5 psi back pressure. Oh, and how do you like the Corvette?

**///M3 CRAZY** · 03-25-2008, 12:33 PM

Originally Posted by chikinhed

I don't want to stay with the AA track pipe because with just the track pipe and no muffler attached to the back of it I was getting 4.5 psi back pressure. Oh, and how do you like the Corvette?

i think you need a set of KK headers and full 3.5 exhaust.... and the vette is really nice....

**Motorsport3** · 03-25-2008, 03:41 PM

I'm curious to see what you find out as well. I currently have a Stromung cat back that seriously has to go. When my car is under boost, it has that Pontiac Sunbird, air through a McDonalds straw sound. I know there has to be something out there that will offer better performance.

**GG///M3** · 03-25-2008, 04:36 PM

Originally Posted by ///M3 CRAZY

i think you need a set of KK headers and full 3.5 exhaust...

+1 I know AA makes a nice race exhaust afew sc guys just added this to there cars, but no one has hit up a dyno yet.

**Mod Addict** · 03-25-2008, 09:40 PM

I would like to see some dyno results of a supercharged setup with the AA race exhaust. I took mine off and installed it on my turbo so I will never know what type of gains I would of had.

**bmwtch8** · 03-25-2008, 10:32 PM

I have ss longtubes and a uuc u, but my cats arent out yet so basically im killing myself luckly they come out next week.

**GG///M3** · 03-25-2008, 11:27 PM

Originally Posted by bmwtch8

I have ss longtubes and a uuc u, but my cats arent out yet so basically im killing myself luckly they come out next week.

your luckyyyyy

**chikinhed** · 03-26-2008, 12:55 AM

All this exhaust work is exhausting. I will be trying another straight through resonator in the system in a couple of days. I don't expect much of an increase in back pressure or much of a decrease in noise but I have to do it. Right now the car is louder than I would like but the sound is awesome. My friends Subaru STI with an exhaust does not sound good.

**four2nothing** · 03-26-2008, 05:03 PM

I've got an AA gen III cat-back.... and a AA C38 that I'm starting the install this weekend.

Does anyone know how well the Gen 3 cat-back flows?

I had a WRX. They've got flat 4 boxer motors. They don't sound good with exhaust... kind of Buell-sounding.

**chikinhed** · 03-26-2008, 11:16 PM

I looked on line at the AA race exhaust and it is a 3" mandrel bent pipe back to a straight through muffler, much the same as I have just built minus the resonator, so I think with the horse power level that my car is at it may flow good enough. The track pipe by itself gave me 4.5 psi back pressure which I am attributing to the restrictive dual 2" pipes that come out of it. The track pipe and cat back exhausts are designed to be replacements for what is installed already, so the dual 2" piping will be the limiting factor for the amount of exhaust you can put through it. At that point the back pressure increases, combustion chamber temps increase, increased risk of detonation, scavenging decreases, and power is lost. AA says that their race exhaust is good for '600+ horse power with out flinching' but my guess is that the back pressure would be quite high at 600 hp. A V8 at thoughs HP numbers would be running dual 2.5" or 3". There is a direct correlation between exhaust flow and HP.

**Jim M3** · 03-26-2008, 11:24 PM

Interesting thread, I think you have really uncovered some new research on the way these systems flow for CF's. Don't you want to have some backpressure to give you some low end torque where the CF supercharge is not fully spooled VS the top end where the supercharger is making full boost. I would think it is a bit of a balancing act. You see sometimes where reducing flow has caused others to loose power and or torque.

**chikinhed** · 03-27-2008, 01:29 AM

I have been doing a lot of reading on the topic of back pressure and the recommendations that the 'professionals' have as far as back pressure. Having 0 psi back pressure will kill the velocity of the exhaust gases which reduces the scavenging effect. It's the inertia of the exhaust pulses traveling through the exhaust system that create a low pressure behind them that draw the intake charge into the cylinder during valve overlap. Apparently the low pressure created by the exhaust is much greater than the low pressure created by the downward moving piston (I think I read it was 500% greater). Also, they say that 2-3 psi should be the max back pressure for proper engine running and ~0.2 psi to maintain 100% open pipe HP. I've been dealing with 11 psi and then 9 psi. I now have it down to 2.5 psi back pressure with no loss in torque that I can feel and an increase in power at the top end that is quite noticeable and smoother.

**chikinhed** · 03-28-2008, 03:10 AM

OK, another update. I added a straight through 18" perforated resonator tonight which gave no increase in back pressure and no change in sound volume. I have a feeling I will have to go to a chambered muffler such as a Spin Tech or large Flow Master to reduce the noise. The Flow Masters are not suppose to be masters of flow in comparison to straight through mufflers like Magnaflow, Borla and Dynomax.

**WK446** · 03-28-2008, 05:41 AM

chikinhed: Thanks for experimenting and sharing!

**chikinhed** · 03-28-2008, 11:50 AM

Having access to a TIG welder helps.

**Motorsport3** · 03-28-2008, 04:56 PM

Originally Posted by GG///M3

+1 I know AA makes a nice race exhaust afew sc guys just added this to there cars, but no one has hit up a dyno yet.

Are these people using the race exhaust on the street? That exhaust is nice but it screams "illegal".

**Jackcat559** · 03-28-2008, 05:55 PM

Great thread! I'm in the same situation. Very low back pressure with a very noisey muffler. Great quality, just too loud.

Presently the car has superpsprint headers into a 3" pipe, 100 cell cat, and a see threw muffler.

These are interesting http://www.cherrybomb.com/products/ The Vortex model uses the ideas of glass packs and turbo mufflers.

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