so i finally went and got a custom dual 50mm exhaust instead of the 40mm
with 1 xpipe and 1 straight thru muffler
the hesitation and bogging and misfiring under loads below 4500rpm totally disappeared.. now 2nd gear WOT @ 2000rpm it lights up the tires like crazy...

also i found out using the diagnostics that my tachometer is wrong, when i was shifting @ 7500rpm, in reality it was more like ~6700rpm ..
so that is something to remember for the swapped people.. the car has really transformed after the exhaust and tachometer discovery...
hope this helps !


im curious though why the exhaust fixed the problem ...could it be too much backpressure was causing detonation under loads ? or too much timing retard ?

if you can't get exhaust gasses out, there is no room for fresh charge of air and fuel. when working properly in correct rev range, the exhaust will scavenge the gasses out, and you get more than 100% volumetric efficiency, it would have been like trying to run a marathon with a sock stuffed in your mouth

IMO twin 50mm is still too small on the S50b30 or s50b32. u have to be at least twin 57mm or twin 62mm as OEM is

IMO twin 50mm is still too small on the S50b30 or s50b32. u have to be at least twin 57mm or twin 62mm as OEM is

Yea, I was wondering why he only went 50mm....?

Hell, mine is 75mm :paranoid:

Yea, I was wondering why he only went 50mm....?

Hell, mine is 75mm :paranoid:Shit, you should have gone 99mm. :eyecrazy

twin 75mm would be good if it was supercharged. single 75mm almost identical to twin 57mm in x-sect area

Shit, you should have gone 99mm. :eyecrazy

Man, look at my ground clearance as it is with these race cats! :eyecrazy:bluecry1

I may have to replace the CAT on my S50B30 3.0L

BMW replacement over $2500

Supersprint Race over $2200

What are the options here

It has to pass emissions test. Up till now been running the Supersprint decat.

Put the original BMW CAT back in for emissions test but it failed on NOx emissions

Now I'm stuck and thinking bout ordering the Supersprint Race but want to know if it will pass emissions

Shockwave & BSH thanks for your help.

I've never looked into it but may be now is a good time for you. Does Magnaflow or any other aftermarket company offer cats that can be welded in place of your old cats? Perhaps you can weld cats in place of the resonators on your SS midpipe.

there are some aftermarket CATS although I don't really like the idea of getting something welded onto my Supersprint decat
I was more interested in the Supersprint Race CAT
If there are some performance gains (as I have heard) and it passes emissions tests I would probably prefer a Race CAT and sell the decat