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Headers are of marginal value in a supercharged application. The point of headers is to create exhaust port pressure that's less than inlet pressure during the overlap period, but in a supercharged application inlet pressure is always positive at WOT so exhaust wave dynamics aren't that important. Also, you don't need or want a high overlap camshaft.
A good set of free flowing manifolds or short tube headers are a better bet than long tube headers designed for a natuallly aspirated application. On a supercharged engine achieving low average backpresssure is more important than harnessing the exhaust wave dynamics.
Look at any supercharged racing engine. The exhaust pipes aren't merged into a collector and they're just long enough to be reasonably certain that the exhaust gases are directed away from the car.
I'd agree if I'd ever seen shorty headers or manifolds that looked decent. All Chevy exhaust manifolds have sharp turns that hurt flow. Shorty headers seem to all have terrible collector designs too. Very steep merging angle.
I'd buy long tube headers, only for the gentler bends and good collectors. No worries about equal length primaries.
Good point, but long tube headers actually have quite a bit of friction. For a supercharged application getting the exhaust into the full size exhaust pipe as quickly as possible will minimize wall friction. The 2.5" rams horns are actually pretty good and they can be ported and port matched to the heads.
If it were me I would survey the market for the best flowing manifolds available.
Thanks for the info - I'll probably just stay with the stock headers and put money into someother place. The new Fastech LSX intake manifold may be a better place to put my money with either the 78mm or 90mm throttle body. Let me know what you think