header primary size on a 496

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header primary size on a 496

Post  72mav on October 1st 2014, 11:20 am

Hi guys,
Whats everyones thoughts about this? 2-1/8, or 2-1/4?
Engine is a 496 with SCJ heads with a 780/720 lift cam, compression will be 13+, stock valves with a 30degree back-cut on the intake valves. and a light cleanup on the ports for now.
Also planning on step design headers with merge collectors. I don't plan on taking it over 7200 RPM
Thanks.
Al
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Re: header primary size on a 496

Post  rmcomprandy on October 1st 2014, 12:23 pm

72mav wrote:Hi guys,
Whats everyones thoughts about this? 2-1/8, or 2-1/4?
Engine is a 496 with SCJ heads with a 780/720 lift cam, compression will be 13+, stock valves with a 30degree back-cut on the intake valves. and a light cleanup on the ports for now.
Also planning on step design headers with merge collectors. I don't plan on taking it over 7200 RPM
Thanks.
Al

Header tube size is mostly reliant upon RPM level and the cylinder size.
That header is to big unless you intend to be above 7,000 RPM most of the time.

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Re: header primary size on a 496

Post  crittersf1 on October 1st 2014, 5:08 pm

I'm with Randy. 1 7/8's are probably more than enough.
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Re: header primary size on a 496

Post  dfree383 on October 1st 2014, 5:11 pm

2" or 2 1/8" IMO

The bigger stuff will make bigger numbers upstairs.

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Re: header primary size on a 496

Post  bbf-falcon on October 1st 2014, 9:33 pm

Too much cam, headers too big, too much rpm.jmo

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Re: header primary size on a 496

Post  68galaxie on October 2nd 2014, 11:56 am

bbf-falcon wrote:Too much cam, headers too big, too much rpm.jmo

Too much cam? The OP did not supply any duration figures.
13+ CR and almost 500" can support a reasonably "big" camshaft for 7000 rpm limit.

2" header primaries will certainly work fine.
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Re: header primary size on a 496

Post  the Coug on October 2nd 2014, 2:04 pm

Personally Al I like the 2 1/8 I figure it is always better to have to much header than not enough....
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Re: header primary size on a 496

Post  72mav on October 3rd 2014, 10:53 am

bbf-falcon wrote:Too much cam, headers too big, too much rpm.jmo

No cam yet. That 780lift is a guess,  somewhere 700 and 800 for sure though.

Another small motor member here was running a735 lift @7100 RPM. thought...... Surprised

Btw, guys thanks for the info.
Regards.
Al
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Re: header primary size on a 496

Post  D. Sea on October 3rd 2014, 1:56 pm

2" Primaries IMO.
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Re: header primary size on a 496

Post  the Coug on October 3rd 2014, 2:04 pm

bbf-falcon wrote:Too much cam, headers too big, too much rpm.jmo



Rick why you say to much RPM? I spun my stock offset crank 7800 for 10 + years, and still looked like brand new when it went East to Kentucky
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Re: header primary size on a 496

Post  bbf-falcon on October 3rd 2014, 6:03 pm

Not saying it won't spin that far,just sayin imo that a pretty much stock scj head doesn't need that much cam or rpm's.

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Re: header primary size on a 496

Post  dfree383 on October 3rd 2014, 6:07 pm

bbf-falcon wrote:Not saying it won't spin that far,just sayin imo that a pretty much stock scj head doesn't need that much cam or rpm's.

That ain't no big cam..... Razz and shifting at 7200 is about right for an engine peaking at 6700.... What a Face
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Re: header primary size on a 496

Post  the Coug on October 3rd 2014, 7:13 pm

I think he has aluminum SCJs
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Re: header primary size on a 496

Post  bbf-falcon on October 3rd 2014, 9:15 pm

That ain't no big cam..... and shifting at 7200 is about right for an engine peaking at 6700....


Now i know why you race dyno's instead of cars. Razz

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Re: header primary size on a 496

Post  rmcomprandy on October 4th 2014, 10:11 am

bbf-falcon wrote:That ain't no big cam.....  and shifting at 7200 is about right for an engine peaking at 6700....  


Now i know why you race dyno's instead of cars. Razz

A step header with 2" to 2 1/8" primary tubes 31 inches long with a 3 1/2" diameter collector 17 inches long is the correct size for a 496 engine at 7,000 RPM ... on a dyno OR a drag race car.
USE a 2" straight tube header primary if the RPM level EVER drops below 5,000 RPM.

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Re: header primary size on a 496

Post  dfree383 on October 4th 2014, 9:21 pm

rmcomprandy wrote:
bbf-falcon wrote:That ain't no big cam.....  and shifting at 7200 is about right for an engine peaking at 6700....  


Now i know why you race dyno's instead of cars. Razz

A step header with 2" to 2 1/8" primary tubes 31 inches long with a 3 1/2" diameter collector 17 inches long is the correct size for a 496 engine at 7,000 RPM ... on a dyno OR a drag race car.
USE a 2" straight tube header primary if the RPM level EVER drops below 5,000 RPM.

And that's what I learned from all the dyno time...... Rolling Eyes

When's the last time your car was on the track Rick? lol!
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Re: header primary size on a 496

Post  bbf-falcon on October 5th 2014, 9:36 am

One thing I learned in 40yrs of racing is that just because my engine will rev to 8k, that's no reason to shift it there . Rolling Eyes and a dyno is not a racecar.

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