Is a 3" exhaust too big?

[Jaydon Fabulous]

I'm looking into a muffler delete shortly down the road, and i was wondering what your thoughts were on a 3" exhaust for our na engines. I was thinking of having them fab up a 2 into 1 3" from the cat back, similar to the supersprint setup. Any idea of the pros and cons of this?

[Incompatible]

Originally Posted by Jaydon Fabulous

I'm looking into a muffler delete shortly down the road, and i was wondering what your thoughts were on a 3" exhaust for our na engines. I was thinking of having them fab up a 2 into 1 3" from the cat back, similar to the supersprint setup. Any idea of the pros and cons of this?

Jaydon, I've had a little bit of time to talk to a few dyno and tech support folks (still ongoing) about the delete project. My understanding at this point is that running a single pipe for the flow/horsepower of our Si cars, the 2.5" dia is fine. 3" will not give you anything other than a little louder volume. For the additional power the M puts out, the 3" would be a better way to go for top end.

Our existing dual system uses 1.880" (OD) tubes. I'm considering the muffler delete at the axle and extending the dual tubes out using 2" dia. tube. Before moving forward, I want to have a "Plan B" in case the delete is to loud. Keep checking back on the "muffler delete" thread we've both posted on.

[S2peed]

That might be a bit too big, the lost in back pressure can result in lost in horsepower. Also it might create a bad exhaust tone.

[Jaydon Fabulous]

Thanks for the great info.

I went on e90 post and saw a couple of the non-turbo engines running custom 3" exhausts. There's even one person running 3.5" piping...which looked a little extreme. Does anyone know the diameter of the supersprint center pipe for our cars? I'm guessing by the look of it it's got to be somewhere around 3".

Originally Posted by Incompatible

Jaydon, I've had a little bit of time to talk to a few dyno and tech support folks (still ongoing) about the delete project. My understanding at this point is that running a single pipe for the flow/horsepower of our Si cars, the 2.5" dia is fine. 3" will not give you anything other than a little louder volume. For the additional power the M puts out, the 3" would be a better way to go for top end.

Our existing dual system uses 1.880" (OD) tubes. I'm considering the muffler delete at the axle and extending the dual tubes out using 2" dia. tube. Before moving forward, I want to have a "Plan B" in case the delete is to loud. Keep checking back on the "muffler delete" thread we've both posted on.

[Incompatible]

Originally Posted by Jaydon Fabulous

Thanks for the great info.
I went on e90 post and saw a couple of the non-turbo engines running custom 3" exhausts. There's even one person running 3.5" piping...which looked a little extreme. Does anyone know the diameter of the supersprint center pipe for our cars? I'm guessing by the look of it it's got to be somewhere around 3".

3" is correct from what I remember. I think I found the size info on the supersprint site.

[Jaydon Fabulous]

http://www.k20a.org/forum/showthread.php?t=46317

Interesting read. It seems that the 3" performs better than 2.5" on this 4 banger.

[Incompatible]

Originally Posted by Jaydon Fabulous

http://www.k20a.org/forum/showthread.php?t=46317

Interesting read. It seems that the 3" performs better than 2.5" on this 4 banger.

(The following is my opinion based on limited knowledge and experience.)
Welcome to the world of dyno and build variables. 1. Lots of variables which are not qualified in regards to the dyno runs. 2. The engine is setup with headers, intake, tune,.... Does that translate directly (apples to apples comparison) over to our cars? For a simple axle back muffler delete I would not think you would see any gain in hp. For a car set up with headers, an ecu tune, high flow cats... the 3" should/might show an improvement over the 2.5".

Borla has a good read on exhaust size under their website FAQ section which is quoted below:

"Q. Is a bigger pipe and muffler system better?
No, there has to be a balanced design to enhance the maximum engine output, exhaust gas velocity, and sound. If the diameter of the tubing is too large, the exhaust gas velocity will be reduced and rob the exhaust of thermal efficiency. Unfortunately we often disprove accepted racer mentalities like bigger is better. We must spend a great deal of energy explaining to someone how a 4" exhaust pipe will not work as efficiently as a 3" pipe. That is hard sometimes, but it is why we have magazine editors. Even with our excellent "track record" winning more professional car races than all the other muffler makers combined, we still often have to prove our theories to very well know top racers. One of these issues is volume versus velocity. The late John Lingenfelter helped us prove this over and over with his legendary Corvette exploits. People were often amazed how he would run 600 plus horsepower Vettes with 2 1/2" exhaust. If 4" would have made John go faster, he would have run it. We need to have a pipe large enough to overcome the boundary layer restriction in a dynamic flow situation while maintaining exhaust speed and evacuation. This isn't a simple axiom to understand, but the second best explanation is to say in race classes where let us say the budgets are seldom limited and the rules are not restrictive regarding exhaust, you will observe much smaller exhaust header tubing and exhaust pipes than some kids run on their 190-horsepower hand-me-down Honda sports compacts on the street."

[Incompatible]

Jaydon, I've been doing some surfing on the 1addicts forum which eventually led me back to the maganaflow website. Magnaflow offers cat back exhausts for both the 128 (NA) and 135 (turbo) cars. The 128 has the N52 with slightly less hp then the Z4 N52 motor. The magnaflow 128 system uses 2.5" pipes while the 135 uses 3". On a side note, look at the size of the resonator/center silencer on the magnaflow system, very large.

[Jaydon Fabulous]

It seems to me like magnaflow thinks the 128 people want a more subtle exhaust, while the 135 is all about performance with the bigger piping and no resonator. I understand that turbo/supercharged cars go with larger piping since they flow better, but i think i'm going to give it a go with the 3" for my z. I'm also thinking of integrating one of magnaflows race mufflers before the tip. They're only 6" long, weigh next to nothing, and couldn't hurt performance.

[Incompatible]

Originally Posted by Jaydon Fabulous

It seems to me like magnaflow thinks the 128 people want a more subtle exhaust, while the 135 is all about performance with the bigger piping and no resonator. I understand that turbo/supercharged cars go with larger piping since they flow better, but i think i'm going to give it a go with the 3" for my z. I'm also thinking of integrating one of magnaflows race mufflers before the tip. They're only 6" long, weigh next to nothing, and couldn't hurt performance.

Are you going to remove/retain the resonators? Don't forget the before and after sound clips. Thanks

[Jaydon Fabulous]

I was just going to do a muffler delete, but now i really want to try to get some horsepower out of the exhaust. I'm going to go 3" from the cats back if it'll fit and get rid of the resonators. Hopefully i'll have this done by summer.

[stoaked]

I had the muffler delete and 3 in tips added on. I think it looks great and sounds incredible. It is however a little loud when it first starts up but after 30 seconds of warming up it sounds great. The 3 in tips fit in the rear bumper opening perfectly. Highly recomend it.