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Expert
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Location: Slidell La. | I have a set of poly flanges and I was thinking of grafting a set of mustang shorty headers onto them,my question is,are the 1 5/8 in. tube on the F**d headers suffient for flow on a stck 2 bbl engine(318)? Thanks for your input. Charlie |
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Expert 5K+
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Location: WHEELING,WV.>>>HOME OF WWVA | CHARLIE------i hope you or PANIC doesn't mind if i give this a shot------CHARLIE-if you have a copy of PANIC'S poly performance-on page 64-65-both third paragraph------i think page 64 states it best
the exhaust port of a 318 is about 1.71 in.-the same area as 1.48 id round tube------using 18 guage tubing gives an od of 1.58-16 guage gives 1.60 and he suggests using 1 5/8 or 1 3/4 as a good range to work with depending motor size and if possible-position the centerline of the primary tube slightly higher than the port centerline 1/16 to 1/8 depending on the primary size and providing that it does not obstruct the bottom of the port opening------it will ipmrove flow
the way i see it is 1/8 won't hurt unless you were boring to a larger cu.in. and use bigger valves to aid in breathing-----------later |
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Expert
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Location: Slidell La. | Thanks Chuck for your help,the flange on the mus stang and the Poly flanges are so similar you could almost mount the mus stang headers to the poly motor.If I could ever get this plan in action,I know that shorty headers are better than no headers.Thanks again Charlie |
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Expert 5K+
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Location: WHEELING,WV.>>>HOME OF WWVA | i kinda think of it this way------you have four head exhaust ports 1 3/4 dumping into a manifold that has one exit port of 1 3/4------if that exit port can handle the four primaries of 1 3/4-it'll handle 1 5/8------the only real part you have to worry about is a smooth transition from heads to primaries-to allow for a smooth flow------don't know if they are still there but there was a nos set of SPITFIRES on ebay----------------later |
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Member
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Location: Long Island, NY | Don't do anything to "transition" to the larger pipe ID. You can enlarge the port, but the edge of the port should be left sharp, no taper or radius. The abrupt change in area forms a very nice anti-reversion ledge that prevents back-flow during overlap, and cleans up your low speed nicely. |
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Expert
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Location: Slidell La. | Panic,what is anti reversion and overlap?I know not of these words.When you have no headers,is there a such thing as bad headers?I have heard people knocking the mus tang shorties,but ...those cars run so well and the headers are so compact they could easily be fitted into anything. Charlie |
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Member
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| There a good and bad headers, typically a bad header is better than a manifold however.
Generally speaking (there are some exceptions)
full length headers > shortie headers > hipo manifolds > lowpo manifolds
anti-reversion - prevent the exhaust from reversing(going back into the cylinder)
overlap - time during which the exhaust and intake valve are both partially open. |
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Header question for Panic
