Headers ,,,
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Safety Car
Joined: Jan 2009
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From: New York
Safety Car
Joined: Jan 2009
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From: anchorage ak
I'm running 1 5/8"" primaries on my 400" only cause that's what I had used on my 350" but 1 3/4" are in the plans. I think at 377 or larger turning 5800 or higher that the primaries size increases. 2" would be a spin to fit on non spread port exhaust, and probably wouldn't help until atleast 421".
Melting Slicks
Joined: Feb 2009
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From: Dallas Georgia
2020 Corvette of the Year Finalist (track prepared)
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You better be spinning that bitch to the moon to need 2" primaries on a small block!
Seriously though, not much of a need beyond 1-3/4" on most small block motors. Hell, I only have 1-7/8 on my 650hp 496 and don't feel they are undersized as I could have opted for larger.
Seriously though, not much of a need beyond 1-3/4" on most small block motors. Hell, I only have 1-7/8 on my 650hp 496 and don't feel they are undersized as I could have opted for larger.
Thread Starter
Safety Car
Joined: Jan 2009
Posts: 4,000
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From: New York
I have the fast burn heads , I am going to go with a 427 SBC end of next fall ... I have just never seen 2 inch primaries on sbc headers .. Sorta caught me by surprise they are even available
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Burning Brakes
Joined: Nov 2012
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From: Indianapolis IN
That's race smallblock territory. Years ago we had a stockcar for a local short track and our next engine was to be a 407" and it was to me to choose between 1 7/8" or 2" headers with the HP peak around 7,000.
I would have used 2" to kill alittle bottom-end, we had an approximate 3 second acceleration window (corner to approximately mid-track) and a narrow rpm range, (1/5 mile oval or figure eight ). We would've needed HP over torque for a push above 5,500
Both partners bailed and the 407 didn't get built. Hope that helps point to where 2" territory is,( imho ).
I would have used 2" to kill alittle bottom-end, we had an approximate 3 second acceleration window (corner to approximately mid-track) and a narrow rpm range, (1/5 mile oval or figure eight ). We would've needed HP over torque for a push above 5,500
Both partners bailed and the 407 didn't get built. Hope that helps point to where 2" territory is,( imho ).
Last edited by 68post; Nov 19, 2013 at 11:56 PM. Reason: stuff
Drifting
Joined: Apr 2005
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From: Central NJ
I can tell you that I went from a 1 3/4" primary tube to a 1 7/8" primary tube on my old 750hp LSX 441 motor and I gained absolutely nothing-Zero.
Keep in mind a 2" primary will need a 3.5" collector if I'm not mistaken and that will kill low end torque on a hydraulic roller setup.
Now if you are building your 427 as a high spinning solid roller with a bunch of nitrous then yes a 2" primary and 3.5" collector makes sense but if you are building a 427 hydraulic street/strip motor I think its a bad choice jmho.
Team Owner
Joined: May 2001
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From: Western NY
Just my $0.02 worth, if you're on the street, and through mufflers, the 1 7/8" pipes are probably overkill. If it were me, I'd go with the 1 3/4" pipe diameter, OR maybe a stepped 1 3/4" to 1 7/8" design, if you can find one for a C-3 chassis.....
Race Director
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From: Corsicana, Tx
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A 2" header will require adapter plates to bolt to the heads.
They will also shove TQ peak way up there. Not so much as change the peak RPM number..but it will definitely be lower under peak TQ. They would help power hang on past peak TQ if you were going 8000 RPM plus.
JIM
Drifting
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From: Central NJ
Thread Starter
Safety Car
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From: New York
Well after looking around , asking and checking a lot I did order the XS 2 inch primary tube headers , They are stepped at the head and go to a 4 inch collector which will connect to my 3 inch exhaust .. Ill put them on in the spring and let post results