Exhaust for M90

[posix]

Have been thinking long and hard about the direction I would want to take the M90 engine when it gets pulled out. Minimum I would want to take the head off from the block and have it inspected then if all is well then replace the gaskets and seals and call it a day.

I was also looking to upgrading the pistons to the CP pistons with multi piece rings and then call it a day.

Brings me to my actual question. (feel free to comment about the engine as well). Will stock exhaust be good enough? Or should I upgrade to like Coupe King SS exhaust? Or something in the middle?

 

[rsporsche]

i have gone through this with my euro b34. i have a new stahl header that i am going to use. the coupeking unit is nice but expensive. there are a few other options. one is from fritzbits in the uk - will cost you about 950 bucks delivered + its stainless. there is a stainless unit from w+n, based on stock, about 1100 delivered (not positive on their shipping). then there is stock, will cost you about 1100 bucks with free delivery + no tax - from a dealer like getbmwparts.com, it is NOT stainless. as @Stevehose says, there is something very nice about that polished tailpipe finishing piece that is part of the coupe.

regardless, use the BMW install parts + hangers,

 

[posix]

i have gone through this with my euro b34. i have a new stahl header that i am going to use. the coupeking unit is nice but expensive. there are a few other options. one is from fritzbits in the uk - will cost you about 950 bucks delivered + its stainless. there is a stainless unit from w+n, based on stock, about 1100 delivered (not positive on their shipping). then there is stock, will cost you about 1100 bucks with free delivery + no tax - from a dealer like getbmwparts.com, it is NOT stainless. as @Stevehose says, there is something very nice about that polished tailpipe finishing piece that is part of the coupe.

regardless, use the BMW install parts + hangers,

thanks for the options. any flow restrictions for a stock setup?

 

[rsporsche]

its not as open as the coupeking system or the fritzbits system. depends on how much additional power you are going to try to pull out of the m90. a good header helps, but in dyno tests with Korman, Jere Stahl stated that the 1 3/8" primary tube of the header was sufficient for all coupe engines (say stage 2 - 230 to 240 hp) with a cam, you don't need to go to a 1.5" primary tube ... unless you have a real fire-breather. i would ask members that have done dyno work on their engines to see if they found a difference. i believe @HB Chris has a stock exhaust with his b35. @sfdon has probably done more dyno work than most, but i hate to volunteer his time.

 

[posix]

I feel like the m90 as it currently is fine for my driving. Maybe i'll put in a b35 crank to add a bit more displacement and a schrick cam along with the piston, rings and rod upgrades along with converting back to FI. Probably will be in the 230 - 240hp range.

 

[HB Chris]

You rode in my coupe with b35, b30 exhaust manifold (not b35) and stock exhaust with all three silencers, I have a mild cam so around 220hp at the flywheel vs 170 stock 8.0:1. Did it have enough power? Don’t spend money when you don’t have to. The stainless exhausts will be louder but sounds like price is the same, the Fritzbits is a great exhaust. You need a leak down test and then a compression test, if that is good, check valve guides and seals and then reseal and drive it.

 

[posix]

Chris's car had enough zip for me haha. Don't plan on doing much enthusiastic driving especially after the resto haha. thanks for keeping me in line haha. i'm just going to for the stock exhaust then. I'll check out W+N exhaust since I like the stainless steel as well as getting it from a dealer as well.

 

[posix]

well i guess. if all the mufflers are good. Can see if I can clean up the existing exhaust system with new mounting hardware and hangers.

 

[rsporsche]

just so you know, the MSRP on the 4 big pieces of the exhaust is around $1400, so if you go that route, price it from multiple online dealer parts groups, free shipping and no sales tax. if you look at your existing, look at pix and determine if its factory or custom. fritzbits is 575 gbp plus 145 gbp shipping ... which is around 935 bucks all in. all of the mounting hardware (new) will be between 150 and 200 bucks. point is, its an expensive proposition. its also something you can replace later. if your existing exhaust is okay, you can consider headers and keep the exhaust you have - later you can put the better exhaust on. this is not something that is going to greatly change the sensation on your 'butt' dyno.

that being said, if you want us to talk you into spending money, we can help you there ... but Chris' advice is spot on. my BEST advice is to insulate the tranny tunnel to slow the heat soak down into the car interior.

 

[Drew Gregg]

The Coupe King stainless exhaust tailpipe has a rounded tip. It can be wet sanded and polished to look like chrome. The W&N stainless tailpipe doesn't have the rounded tip. I'm sure it can also be polished. Here's the Coupe King tip.

 

[Markos]

Nobody wants to hear about it your m90 problems @posix!

 

[OCCoupe]

@posix Stahl headers are great, so are Super Sprint headers. As Scott mentioned W&N's exhaust and Fritz Bits exhaust systems are great. I used the Fritz Bits exhaust and was very happy with fitment and quality. Plus they are good at communicating. Fritz Bits claims a 20% flow increase over stock which is good since you have extra displacement over stock. The CoupeKing exhaust is a bit more hot rod-ish. I like it but would be done with it in about 30 minutes of driving. It is loud and raspy; but this is my personal opinion.