Another header question

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Another header question

Post  kjett on July 20th 2012, 2:07 pm

Anyone have pipeworks and want to plug in some numbers for me to come up with header needs? I'm putting together a little A headed 488ci motor and want to see if I'm good with using 2 1/8" primaries and 4" collectors. Also thinking right around 30" would be the correct length, but would rather see if I need longer or shorter for my needs as well as collector length.
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Re: Another header question

Post  Lem Evans on July 20th 2012, 2:53 pm

kjett wrote:Anyone have pipeworks and want to plug in some numbers for me to come up with header needs? I'm putting together a little A headed 488ci motor and want to see if I'm good with using 2 1/8" primaries and 4" collectors. Also thinking right around 30" would be the correct length, but would rather see if I need longer or shorter for my needs as well as collector length.

2-1/4" i.m.o.

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Re: Another header question

Post  kjett on July 20th 2012, 2:55 pm

Then that's the answer. I need to get the tube, collectors and flanges. Just wanted to get the right stuff the 1st time. What's your thought on collector size/length? Still good with 30" long tubes as well?
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Re: Another header question

Post  fc2444 on July 20th 2012, 3:04 pm

I would go 21/8 to 21/4 step and 4" collector

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Re: Another header question

Post  kim on July 20th 2012, 3:51 pm

The only reason to do a stepped header is to maintain sufficent velocity in the exhaust charge as to use it for a scavenging affect in a restricted intake combination.

Ideally, let it dump from the port in the head, if the intake isn't a problem. If the head will have between 75 to 85% exhaust to intake capability, go with the biggest damn primary tubes you can fit. 2 1/8 or 2 1/4 are used because of head design and spark plug access. If you can get 2.5" primary tubes in there, then go with it.

Now this is all predisposed that your looking for peak HP, if your in fact looking for improving low RPM performance and torque, then exhaust gas velocity and scavenging is very important.

Do you alreay have a cam? Is the cam mapped for something in particular, or will you get a cam mapped after you decide on header capability.

Want a complete package, flow bench the carb/injector intake, head for intake flow, then flowbench the head and exhaust, complete, then map a cam to maximise both.

Will this combination have mufflers?

Will it dump at collector?

If looking for hiemholze advantage, its going to depend on RPM of the engine, and which harmonic you intend on using, but for about 9200 RPM its 36" from valve to header opening. sooo if your looking to spin it that high, with 6" in the head runner, then 30" is perfect, but if its in a conventional chasis, leaves the collector about even with a fire wall.

4" collector will work, but will actually load and add pressure at peak RPM even on something that small. If your going to go 2.25 to 2.5 primary, might as well go with a 5" collector.

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