Dual to single exhaust?

[direction88]

I am going to have a new exhaust built for my car and I want opinions on my idea. I should be picking up a set of headers soon and I want to run a Y pipe to a single 3" tube into a Borla. Is 3" going to be too big/small? I have a 2.7 stroker so it breathes a little deeper than a 325i. Please give reasons as opposed to just telling me its too big/small. Thanks!

[rkettner]

i bet that will be loud. real loud.

[E30M3]

Alot of very built up s14's and turbo s14's run a 3" pipe the entire way, kinda loud but very beneficial. It might be over kill on a 2.7L, but its has been done on a e30. Good luck I'd like to see it.

[Eugene]

On top of being too loud, you will kill your bottom end torque (which is one of the benefits of a stroker right?), because your exhaust velocities will reduce dramatically.

The reason why the factory puts 2 X 1.5" pipes is for noise suppression and to keep the velocity up. You really haven't done anything to your car except increase the compression slightly and add 0.2L to the displacement, so if you are expecting a power increase by increasing the exhaust you will be disappointed, although you might get the impression that you are going faster when making more noise.

Exhaust mods are one of the last things to do, as with most of the design of the BMW, it is extremely efficient from the factory which is why you don't gain 10-15RWHP like you do from a Honda. At best with a N/A performance engine one might gain ~3-8 RWHP, depending on the depth of modifications and if the exhaust has been matched accordingly. Most guys go aftermarket/custom for the weight savings as the stock exhaust is pretty heavy, and you might shed 30lbs by doing so.

Some of the m20 forced induction guys put 3" exhaust, but that is to support ~260+ RWHP. For your application I would leave it stock for the ease and cost of installation and the fact that it is really easy to do yourself. I know it is not what you want to hear Liam, but it really depends what you want and what the end product of the car is going to be. If you insist on spending the extra money and refuse to go that route, a single 2.5" would be the largest you should go.

Good luck.

[direction88]

Eugene's legs + a vice. JK! No I realize that 3 is overkill but I do need a new exhaust (to go with your old headers) and I want something that will be worth my money. I was thinking 2 3/4 but I have been looking on r3vlimited and 2.5 sounds like the right diameter. Now my problem is finding a decent single inlet dual outlet muffler so I don't have to put something on that makes my car look ricer or 318ish! Any suggestions for a decent looking muffler? I looked on the Borla home page and they don't offer anything like I'm looking for.

[DS Rook]

Check Magnaflow website. They have lots of options.

[direction88]

Originally Posted by tuvw412 good......Good article-Here, I really learned a lot of things sem

WTF? Sorry did we not deliver on this thread for ya son?

[320iCar]

i would go for a 2.5" single exhaust. since you are naturally aspirated, thres no big rush to get air out. a little backpressure is always good. just a little. and plus, 2.5" is still pretty big. i can understand a twin turbo supra running a solid 3" exhaust, but thats because they use every inch of it. if you use 2.5" or even 2.25" (thats what im running, 2.25" turbo back stainless on my m10) you can not only have alot of flow, but also tune the sound to how you want it, not just loud like a 3"

[Mark D.]

Originally Posted by direction88 Eugene's legs + a vice. JK! No I realize that 3 is overkill but I do need a new exhaust (to go with your old headers) and I want something that will be worth my money. I was thinking 2 3/4 but I have been looking on r3vlimited and 2.5 sounds like the right diameter. Now my problem is finding a decent single inlet dual outlet muffler so I don't have to put something on that makes my car look ricer or 318ish! Any suggestions for a decent looking muffler? I looked on the Borla home page and they don't offer anything like I'm looking for.

dammit Liam, get that cars plastic bumpers on with paint instead.......:-)