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Old 04-01-2013, 06:44 PM
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SBC header tube diameter

Im sure this question has been asked before, but ill ask anyhow!!

I have a 400 sbc punched out .040'' making it a 408, I am supercharging it to- estimated 6-8 psi.

After the header collector will be 3'' pipe leading to X pipe with 3'' cut outs. after the x it will drop to dual 2.25'' pipes out the rear.

I understand with cutouts closed im limited to the 2.25'' pipe, but will i benefit from larger headers when factoring 3'' cutouts?

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Old 04-01-2013, 09:07 PM
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What kind of horsepower will it make 650? or more. You need at least 1 3/4 or 1 7/8 headers. Get rid of the 2.25 inch with that motor as there is no benefit. You need at least 2 1/2 and better with 3 inch exhaust. The 2.25 wont expel the exhaust quick enough as it starts to build power.
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Old 04-01-2013, 09:28 PM
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I use 3 inch mandrel bent exhaust with an X pipe,2 1/4 is a joke.
My primaries start at 1 7/8 and step to 2 inch with 3 inch long collectors,my engine is N.A.
You should make more power than me so you need bigger
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Old 04-02-2013, 02:45 AM
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I would advise you to go no smaller then 2 1/2" pipes....and 3" would probably be even better. You're going to need that engine to breathe. The last thing you want is backpressure with a supercharger. I ran a smallblock with small diameter pipes with a blower in the past...I blew it up. It matters more how much you can evacuate from the engine then what you can force into it.
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