I have a bone stock 70GS455(except for HEI and open element air cleaner) and was considering some ported and polished(if thats even possible) exhaust manifolds. Since I just purchased a new 2 1/2' Torque Tech exhaust system with the long case Walker Dyno Max mufflers but have not installed it yet I figured I might could swap to some better exhaust manifolds when installing the new exhaust system. I remember when I first started racing dirt track someone was modifying the exhaust manifolds for the SBC by porting and polishing the inside of them. I think they may have used some sort of extrusion process... Anyhow I was wondering if any of you folks were using this type of manifold and if so how much of a horsepower/torque increase could be expected? What is the cost and finally does anybody have a used set for a bargain? Thanks for any info and all replies. All opinions are welcomed. Thanks Bert
Greg Gessler does them, you can check out his website at http://www.gesslerheadporting.com/ you can probably do a search on ported exhaust manifolds on this site and find a bunch of info as well. I have a set and I know Carl Rychlik does too, since I bought mine from him when he bought new ones. :TU: I have no complaints about them, but I couldn't tell you if I picked up any horsepower from them, since I made a bunch of changes at the same time.
i asked greg about extrude honing my 340 manifolds,as the poston headers may/may not fit according to some posts i saw.he said about $400.i wouldnt go that route unless you want the stock look uzzled: he recomended spending that on porting the heads as a better investment.
Opening up the dump from 2" to 2.25" will net you about 5 hp and .05 in et. Cost for this will be roughly $200 unless you know the machinist quite well. As Greg says your money will be better spent else where.
