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Old 09-11-2004, 11:38 PM
Brian Morency's Avatar
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Exhaust manifold vs. Headers

im am wondering how much more perfomance headers will give a 350sbc over the stock exhaust manifold? and what are the benefits of headers over an exhaust manifold? will it increase hp and by how much?
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Old 09-12-2004, 01:03 AM
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Brian I think it's pretty much accepted that the benefits headers give over cast iron manifolds are inline with performance mods done to the engine. The more stock an a engine is, the less the performance is gained by fitting headers. Of course, many will dispute this because usually the rest of the exhaust system is replaced, along with the headers, accentuating the performance gains. I've been curious about this too for quite some time and have been observant when ever test comparison results were available. From what I know, it would be safe to say that a stock engine with headers would gain between 15 to 30hp over stock manifolds. Of course if you've got a free breathing monster that consumes a huge amount of air, then the gains made with headers would be in the 60+ hp or more region. Then you've got headers of differing designs and primary pipe diameters, like 4 into 1 systems and the tri 'y' setup. I've read conflicting reports, but I think that the 4 into 1 system excel at cylinder scavenging - using the negative exhaust pulses to great effect to boost high RPM performance and therefore HP. But the scavenging effect can go against a street motor when it's 'off the cam'. The tri 'y' system on the other hand is generally free flowing and should give you a power delivery boost that you can feel in the seat of your pants. That's what I know Brian, but hopefully there's an exhaust fitter out there who can give us some of his knowledge.
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Old 09-12-2004, 08:08 AM
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Club, thats about right. If you put headers on a stock engine, youll notice a little more low end torque( if there full length especially).the higher the RPM scale the engine revs, the more beneficial headers become
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Old 09-12-2004, 08:12 AM
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Hot Rod magazine just did an interesting article regarding header selection and collector tube extension choices. Basically the had four identical headers except for the primary tubes were different sizes. They also used a set of collector extensions and cut them down an inch at a time to see if it affected the power at all. The main idea of the article - if you're not runnng 18" collector extensions with your open headers you are leaving a fair amount of power on the table.
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Old 09-12-2004, 09:24 AM
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What is a collector extension?Does that go on the end of a full length header?Thanks bm
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Old 09-12-2004, 10:52 AM
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From what I've seen I think the 'Rams Horn' cast iron manifolds in 2" or 2.5" can flow pretty darn well.

For headers what I'd like to try are 'Tri-Y's but I think only 1 company makes them and only for a limited amount of aps which doesn't include mine. Maybe some day I'll find some old rusty Tri-Ys and see if I can trial fit them as an experiment or see what it could take to modify them to fit.
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Old 09-12-2004, 01:06 PM
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Quote:
Originally posted by batman09
What is a collector extension?Does that go on the end of a full length header?Thanks bm
Its only application is for cars that have no exhaust system. Like race cars, or cars that belong to jerks for example (grin). Some people think just having the open headers is the best way to roll, but these guys proved that if you attach a foot and a half of exhaust tubing to it you will pick up some torque all across your rpm band.


Looked like this, but the ones pictured here are only 12"

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Old 09-12-2004, 03:20 PM
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aah ic. i guess i might just have to get those when i pick up some headers, i guess i must be one of those jerks, right now im running just an exhaust manifold with y pipes.lol until i get header's,
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