What's the deal with porting them? do I just go crazy with my porting kit and open them up/smooth things out, or is there more of a science to it?
I've done porting myself, and have read books on the subject. Manifolds should be fairly hard to mess up, in my mind. With heads, you have to remember not to open up the exhaust ports larger than the manifold / header. Don't open up the intake manifold ports larger than the intake port on the head. Manifolds are at the end of the line. Open up the individual ports, and the dump, where the exh pipe hooks up. Don't go nuts, however. If you were to open the exh manifold ports way huge, you'l just invite leaks and slow down the velocity. Gasket matching should do the trick!
72skylark, Opening up the outlet can only help you, as long as the head pipe is large enough. The individual runners require a little more finesse to extract good flow. If you don't feel like attempting this yourself, send them to me.
Good Idea Greg, I think I'll bring a set of 455 exhaust manifolds up to you when I pick up Scott's heads. I have about 5 sets, anything in particular you want in a set? Do you offer an exchange set, as long as I'm up there anyway..?:grin: How about price?
Re: Good Idea Al, Personally I would use an early 70's style that originally came on the car. I can do up a set, and you can drop off your exchange manifolds when you pick them up. Whatever casting #'s you plan on exchanging are the type that I will modify. Price is $345.00 with exchange, this includes boring the outlet oversized, porting and polishing the individual runners, bead blasting, painted with high-temp Eastwood paint. Comes with new studs, brass nuts and installation instructions. This manifold will satisfy 95% of GS owners, the other 5% are Stock Appearing racers that are looking for every last bit of power. For them, additional work is performed such as internal welding. I also have available Stainless Steel exhaust manifold bolt kits. These are the bolts that attach the manifold to the heads, say goodbye to rusted bolts! !
Greg, given the price, do your ported manifolds offer the same or better performance gains that a brand new set of TA Competition 350 headers? Just wondering if the costs vs performance is worth it.. Used headers are impossible to find, new headers are so exspensive, but exhaust manifolds are a dime a dozen and I'd imagine a decent die grinder and some carbide burrs can make 'em at least a little better... Dan
Dan, Cast iron exhaust manifolds (even ported) do not afford the engine an opportunity to scavenge the exhaust gases the way that a header can with its long primary tubes. But in a street (mild cam) application running thru a full exhaust system there is not as great a difference as you would expect. Years ago at a track rental, I performed the following R&D on manifolds. I switched my 1 7/8 KB headers to stock untouched 455 exhaust manifolds. I actually did this switch at the track. I made the head pipes before hand so that I knew every thing would fit. I ran the car at the track with the headers and switched to the untouched manifolds in the pits, and made a few more passes. With the headers running thru a 2.5" exhaust system the car was running 11.60/70, with the manifolds I ran 11.90/12.00. The difference was 3 tenths and 3 MPH. Less loss than I anticipated. Ported exhaust manifolds generally run about 1.5 to 2 tenths faster than a set of pure stock manifolds. Internal welding gives additional gains. If you dont feel up to attempting to modify the manifolds yourself, give me a call. If you want to keep your car looking original or you like that sleeper look, Ported manifolds can't be beat for cars that look stock, yet fly down the mile.:TU:
