I plan on putting factory manifolds back on my 70 mav im tired of all the header leaks my car is street driven ,I plan to run 2 1/2 pipe at the rear end with turn downs and flow master mufflers I don't know what cam I have but its lopey and has great throttle response with a rpm intake,600 holley and Mallory ignition will I hurt my performance a lot?
it depends on your heads. if they flow well the manifolds will consume a noticeable amount of power. most 302s dont need 2.5" exhaust. 2.25 usually has better performance. a motor needs exhaust back pressure to run efficiently. chances are with the stock manifolds you will have plenty of back pressure and the exhaust pipe size wont have much effect on the motor.
No engine "needs" backpressure. There are plenty of threads and articles on that subject if you want to research it. 2-1/2 inch pipes on manifolds with a 2-inch outlet kind of defeats the purpose. It will run fine with the stock manifolds, however power from 4000 and above will be reduced compared to headers.
What style ? Ball and socket or three bolt flange ? If it's the three bolt, what gasket are you using there ? The asbestos (white) ?
Before you go to the trouble of replacing your headers with manifolds and reducing your horsepower why don't you try some copper collector gaskets or aluminum or cut the flanges off and go with straight 3" exhaust pipe right to your header with a band type clamp like what summit sells? Then you can reduce to whatever size pipe you want to use.
This is what I was getting to. Those white asbestos gaskets are about the worst thing you can use with headers, at either end. They WILL leak, if not sooner, then later. Soft copper or aluminum works 200% better and rarely ever leak.
i think it has the paper gaskets,i haven't done any of this work to the car the previous owner built this car im just changing a few things.the exhaust work is very crappy workmanship I, 2 3/4 pipe ran all the way out the back with those cheap rond turbo mufflers ,it was mounted up with crappy hangers it shakes and rattles against stuff that's a lot fo the problem I think ,either way I go a new exhaust system in the future.Has anyone heard of using som eflex pipe to help keep the stress off of the header gaskets? I talked with a guy who use to work in a muffler shop he said every car that he has installed flex pipe in the system hasn't had any more header leak problems ,he says install them as close to the header collectors as u can to keep stress off of the gaskets up top and down below
With a decent sized cam.. that motor will be down an easy 15-20 horse with restrictive factory manifolds. And what's worse.. you'll lose torque everywhere past about 1500 rpm. Fix the issues and go about enjoying tubular headers like the rest of us do. Remflex gaskets will not leak either.
As far as collector gaskets go..i found most of them do leak..i tried a new carbon one about 2 years ago and keep using it, i think its 12 bucks for 2 gaskets and they never leak. mind you i took my exhaust off like 5 times since my first set and i keep buying them..that proves they are good
