Quote:
Originally Posted by porsche986spyder
With no O2 bung wholes for the sensors I hope you plan on keeping the cats at least in the headers on. Otherwise you will get your cells to come on and stay on. Or you can do vice versa, delete the ones on the headers and keep the ones on the secondary down pipes. Either way, you can only delete one set(pair) with out any problems but not bot sets(all four). Not to mention the problems you would have with passing emissions. The real question here is which set of cat deletes gives you more power, the ones located in the headers, or the secondary ones? Any one know? I would bet deleting the ones in the headers would be more to benefit from. 
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I have tried every combination several times for various reasons on my 2000 S which has O2 sensors before and just after the primary cat which is part of the header.
1) Just the Fabspeed bypass. A bit more throttle response, noticeable deepening of sound, and no chance of CEL. Sounded awesome with PSE.
2) Maxspeed headers w/bypass. VERY noticeable increase in throttle response. By far the single largest power mod. One CEL in about 1,500 miles of driving. 30 seconds to clear and never came on again. Headers have 2 O2 bungs so just reattached sensors. Sound was very disappointing. I thought it would roar but sounded ricey and tinny. Was told that cats reduce high frequency tones.
3) Headers w/oem secondary cats. Gains from headers still felt strong. No CEL yet. Sound is awesome. My vote for best combo.
I had the headers off for a while and really noticed a loss in power. Felt flat.
On these Stebro bypasses, they really do not compare with the quality of the Fabspeed pipes. If you were to look at the two side by side and look at what you are getting for your money, I think that the Fabspeed is a better value.