[NZCOBRA]

I have just recently bought some Flowmaster Slimline mufflers 13530320,like a HP2, these are 4 1/2 OD and have 3 1/2 ID listed and are made of 304 , the internal hole is a lot smaller than expected maybe 2 1/4- 2 1/2 cant measure properly , you have to tig weld your own ends on . Car is still quite loud, actually 1 db less , I tried a different exit pipe that had a 2 1/2 inside the 3 1/2 that exits inwards and down that made the car 5 db quieter , OK on the road but not so good for dusty /shingle drive ways , Haven't gone back to dyno to see if the 408 makes more or less that 554 flywheel HP .The air cleaner I designed and had machined cost me 5KW it is an 11x3 made into an oval , the EFI throttle bodies have bigger linkages to clear ,It is hard to do much else .Cheers