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Old 07-29-2004, 11:28 AM
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Headers size help

Are there any formulas for finding the correct header tube size based on cubic inches. I have a 408ci motor and will be having custom headers made next week. Do you guys feel 1-3/4 primary tubes are big enough for a motor of this size?

408ci windsor
2.08/1.60 alum heads
Roller cam 3500-6800rpm
250shot nitrous
3500stall C-4
victor jr int/ 850holley
10.75:1 compression

What are you guys running for header size on something 400 to 420 cubic inches?

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Old 07-29-2004, 12:04 PM
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I was feeling insecure about my size once too, but she told me its not the size that matters.

Does that help?

JK 1 7/8 I think would work better for you, its hard to go too large on an N20 application.

K
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Old 07-29-2004, 12:21 PM
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[QUOTE]Originally posted by killerformula
[B]I was feeling insecure about my size once too, but she told me its not the size that matters.

that was funny,

Im not insecure because im usualy blown


ok, I guess I will go with the 1-7/8 I was just worried that it might be too big for daily driving. I measured the opening on the heads and it measures 1-3/4. Do you think a 1-7/8 header is going to make a difference if the exhaust port on the head is only 1-3/4?


Ben
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Old 07-29-2004, 01:54 PM
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its probably not worth the effort unless you're going to port the exhaust. Just my best educated guess.

K
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Old 07-29-2004, 02:25 PM
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ok, thanks for the input


Ben
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Old 07-29-2004, 02:37 PM
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The ledge or step left from the port to header differences will provide a sort of reversion barriar that will help prevent gasses from being pulled back into the chamber while the cams in overlap. DON'T port match that. It helps build Mass density in the cylinder.
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Old 07-29-2004, 03:01 PM
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What ledge? I already ported my Header flanges to match perfectly with the heads, they are ported to a 1-3/4" in a D shape. I ported these exhaust ports with the header flanges bolted on with copper gaskets, so there is not a ledge, its all a perfect transition through out the port to header flange.

is this ok?


Ben
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Old 07-29-2004, 04:15 PM
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Quote:
Originally posted by brainsboy
What ledge? I already ported my Header flanges to match perfectly with the heads, they are ported to a 1-3/4" in a D shape. I ported these exhaust ports with the header flanges bolted on with copper gaskets, so there is not a ledge, its all a perfect transition through out the port to header flange.

is this ok?


Ben
It will be ok as long as they get aligned perfectly when installed. If the headers flange opening is larger than the port it helps prevent exhuast reversion at lower RPM.
You're kinda committed now because there isn't enough thickness to try and port out your header flanges.
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