Re: backpressure and hurt valves
I'm not sure about the new big blocks, but I know that newer, emissions SBF's need a fair amount of back pressure to run right. I have an '86 F150 4x4 w/302 and I took the rear cat off, hollowed out the front one and just ran glass packs. The truck ran like complete crap. I took the glass packs off and put on a Flowmaster 40 series Deltaflow muffler and it ran a lot better. I did some research into that and found out that the cam timing of the emissions engines needed some back pressure to operate correctly. It doesn't make any sense to me, but I guess I'll believe them. But the valves won't get hurt if you run a full exhaust plus a cat. Look at race engines that run open headers. A lot of those engines run a season or more before being pulled apart and freshened up and they dont have any valve problems. I'd say if you ran just the stock manifolds, then I'd worry, but you have nothing to worry about. Just my opinion.
1982 F100 2wd-408c CHI 3V 225cc Heads, 3v Intake, Pro Systems 1000+HP carb, email@example.com w/ 0.694/0.697" lift solid roller, JPT Rollerized c6 and 5000 rpm converter, 4.86 gears and S&W Ladder Bar kit with QA1's all the way around.
firstname.lastname@example.org mph 1/8 mile with lots of bounce - with old engine and suspension(should be greatly improved)
1982 F100 408c 3v