TBH, when I put the cat bypass pipe on my car I felt no improvement in BHP at all, if anything an ever so slight decrease, I remember someone once telling me that the F could do just this due to a loss of back pressure or something like that, makes a better sound though, especially when you have a sports box on the back, I’ve not put mine back on yet anyway.
dunno how he came to that conclusion no offense when i had my 214 exhaust install i went to longlife and had a custom stainless steel exhaust on with a de-cat.
Now the firs thing i went to a RR day a month before i started moding my car and the car put out 103bhp that was with no mods at all
then after the exhaust i went to the same place tommys rollers in cardiff so see the improvment and the RR dyno put out 115bhp :S as you see a very big increase plus the car felt so much better.
Now the cat only sucks power away from the car so i can tsee how a standard cat could be anywhere near the same perfformance as a de-cat pipe can anyone point in the direction of a before and after dyno for mgf???
Plus the diameter of the de-cat pipe is much smaller than my one on my rover 214 meaning very little loss of back presure
taken from a FAQ site... There is some debate about the benefits of de-catting. Most 'experts' agree that merely removing the cats won't cause any problems as long as the Lambda sensors are left in place, and that the ECU does not need re-mapping. Simply replace the cats with equivalent lengths of exhaust piping. The main debate is whether the ECU automatically makes the most of the cat-less exhaust, or whether re-mapping is required to maximise the benefit. The consensus now appears to be that re-mapping, although optional, will increase the power over and above that gained by merely removing the cats
i havent a clue about the technicalities of it all, but i know of a few ppl who own mgf's who have suffered a loss of power after fitting a car by pass, the only gain they got was an increase in noise.
and dont take any offence from me, but i wouldnt compare a rover 200 to an mgf, as the design and outlay have similar parts but on the whole completeyl different.