Well, I've developed an exhaust leak so it looks like it's time to do something about it. And here is my question: What are the pros and cons of switching to headers or getting the exhaust manifolds ported?
I've tried both, here's some thoughts: You can hog out your manifolds yourself with about 3 hours, a good die grinder, and an industrial sandblaster. Certainly flows better, bot *that* noticable a change though. A good clean $0 add-on. Headers have a bigger up front cost, they should be coated to protect your investment, and you'll need to rework your exhaust to work with `em. Better performance, noticably so, and you'll get a slightly different note from the 455.
On the big cars, the problem with full length headers is crushing them against speed bumps, rolled curbs, etc.. Shorty headers were not an option back in my days. The increased header noise (pinging/tinging) can grow tiresome to those who prefer the sound of their stereo system and quiet interiors. On a factory engine (small valve, small cam, 2.93:1 rear) there may be no practical increase in street performance by just adding headers alone. My friend's 455 Riv (small valve stock heads, 2.93:1 rear) ran a Kenne-Bell 1H "Family" camshaft with full length headers. Changed back to stock exhaust manifolds and told me there was no loss in performance.
Hey thanks guys. While true that my 455 is currently stock, I'm planning more of a build up, over the years, replacing as things wear out and money allows. I know shorty headers are the only ones that will fit, and my entire exhaust line is pretty well shot, so reworking the exhaust around the headers isn't a huge deal. I'll have to mull it over for awhile.
Aside from your exhaust.... I'd start with an oil pump booster plate and an electronic ignition conversion. Personally, I don't like the looks of the factory HEI units and would not install one in my boat.
Ah, go with the headers if you're rebuilding the whole kit. Bang for the buck though, I favour a carb and HEI rebuild (using an external coil). If the appearance of the HEI bothers you, check out davessmallbodyheis.com for a good clean conversion.
