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I would prefer to stay with a stock exhaust system (new) on a turbo build (M30B34). Was hoping for 300-350hp in the end. Is this possible/reasonable with the stock exhaust?

It will be tough as the stock exhaust will choke the $#%% out of the system.

It's not just the power, but turbo responsiveness and spool will be greatly diminished as well. BMW got 250 hp from the 745i system with near-stock sized pipes. I wouldn't expect to get higher than 250-300 (maybe) with a stock b34 system. Seriously though, do a proper exhaust for it. Sell the new exhaust system you have to someone who needs it. You're going to have to hack it up to make it work with the turbo anyway. This is no time for that degree of penny-pinching. If you don't have the money to complete the project with a new exhaust right now, wait until you do. Do it right the first time.

That's my $0.02 anyway.

If its a new OEM exhaust then selling it could pay for the custom one and then some other goods. That exhaust is not exactly up to the task. It would "work" but...

What about the stock M5 exhaust?

derrith wrote:What about the stock M5 exhaust?

If you're going to change the exhaust, change it to something that'll do the job properly. Again, it'll "work", but it won't work well.

A better NA exhaust is not a better turbo exhaust.


Hopefully redundant answers are better than one

Understood -- stock exhaust + turbo = no good