hello loc.i have decated my 99 is200 . where the precats were i think i should cut the pipes out and replace with smaller diameter ones as to keep some back pressure.car runs ok without but think they should be smaller diameter pipes.any comments would be apreciated.thanks

Yeah that sounds about right,

Your talking about on the manifold yeah? As long as the pipes aren't small than the normal pipework (ie the bit before and after the precats) you should be ok.

Good job fella.

Stav

NO! keep the pipes the same diameter.

ok. will try explain a little more .where the 6 pipes from the cylinder head meet there are 2 precats one for each 3 cylinders.where the cats are housed the pipework is approx say 4" wide and say 8" long then tapers down to say 2" and then carries on to the rest of the system.it is the cat housing that ime thinking of taking out and replacing with a smaller diameter pipe.possibaly the same diameter as the 2 down pipes which leed to the 2nd section of the exhaust.car runs fine at the mo but thought it may need more back pressure.thanks folks

sorry miread your reply.will get me hacksaw out and make it so its the same diameter from before and after the precat housings cheers

doing thats fine - thought u meant putting even smaller pipe work in......