hi all, having read various threads about de cat pipes I am still a little in the grey about true gains from putting a de cat pipe on my 20v turbo. I have a Front mounted intercooler, upgraded turbo, exhaust system, blow off dump valve, gtec 2 chip, cone air filter. what

can someone clarify if I was to put a de cat pipe on what would I gain in relation to bhp, torque etc...?

cheers in advance

Phil

I'm not entirely sure about the gains but it does sound nice.

Faster spool due to less back pressure.

Decats make quite a significant difference on turbocharged engines (not so much on N/A engines). Slightly lower boost threshold, as Joe mentioned, and also a significant increase in performance. The more highly tuned the engine, the greater the difference in performance. On a relatively lightly modified engine such as yours, a decat would give the feeling of a nice increase in throttle response and acceleration. On a dyno you might see a difference of 10 bhp. More importantly you should see a slightly wider spread of torque. The only downside is having to put the cat back on every year!

You'll also get stronger boost at higher revs, again, due to lower back-pressure

Quite simply, at anything over about 5,000 - 5,500 rpm, the turbo runs out of puff, as it struggles to overcome the backpressure in the downpipe (partly caused by the downpipe being small and partly because the cat is restrictive)

Removing the cat removes part of the restriction and allows better breathing - you'll notice you can reach 6,000+ rpm before the boost starts to tail off

Its at this point that you start chasing each new weak point as it becomes apparent - what next? bigger downpipe? - that'll sort the weedy standard downpipe's restriction. Damn, now the standard 2" V-Band adapter to the turbo is the restriction - new turbo? Great, now its the injectors, etc etc ad-infinitum

Its a slippery slope....