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1.625 header rule

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1.625 header rule

Postby RCJ » Fri Dec 02, 2011 6:14 pm

Building a new motor for a 3200lbs street stock camaro.Rules are 350cid ,flat top pistons ,unported vortec heads,.480 lift cam(250/254 on 106 installed at 102 solid flat tappet)any intake, spacer and carb,1.625 diameter headers.Peak power is at 6200 to6400 rpm ,480 to 500hp.
In car video shows that on corner exit he is at 5900rpm when he goes to WOT then pulls to 6700.
I want to increase power in this range(5900 to 6700).I've been using off the shelf Schoenfeld headers 30'' long with standard collectors.Pipe max recommends 30'' to 33'', 1.632 to 1757 diameter,2.5 to 3.5 by 17.4 megaphones or 3.0 to 3.25 by 17.4 straight collectors.
Will merge collectors help power in this range?I have some 1 .750 flanges if I flare the 1.625 pipe to fit will this create a lower pressure area when it necks back down to 1.625?Or build a header that is the exact diameter of the exhaust port which is smaller than 1.625.Then make a smooth transition to 1.625
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Re: 1.625 header rule

Postby MaxFlow » Fri Dec 02, 2011 6:39 pm

What compression is the engine and fuel? Carb?
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Re: 1.625 header rule

Postby RCJ » Fri Dec 02, 2011 7:05 pm

11.5 c/r ,A mix of 50/50 sunoco 110,91 pump gas
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Re: 1.625 header rule

Postby #84Dave » Sat Dec 03, 2011 10:43 am

If you want peak torque to occur near your 5900 rpm corner exit speed, your header primary OD/ID would have to be larger than 1.625". Header primary pipe ID/area determines peak torque rpm. The Jim McFarland formula, used over many years, will get you very close;

Peak Torque RPM = Primary Pipe ID Area x 88,200 / Single Cylinder Volume............ or..................
Primary Pipe ID Area = Peak Torque RPM x Single Cylinder Volume / 88,200

-Dave-
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Re: 1.625 header rule

Postby DaveMcLain » Sat Dec 03, 2011 11:04 am

I think that the header is probably ok but really I think you need might try a bit more cam or take the one you have and knock it back about 4 degrees to see if it runs better.
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Re: 1.625 header rule

Postby panic » Sat Dec 03, 2011 11:15 am

New cam: exhaust opening 4° earlier.
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Re: 1.625 header rule

Postby RCJ » Sat Dec 03, 2011 6:31 pm

I could change cam timing but, I'm really trying to think outside the box and get an edge on the competition.
Expanding the pipe at the head then reducing the size.Wouldn't that create a low pressure area when the gases speed up in the smaller pipe?
Making the pipe the same size as the exhaust port then a smooth transition to 1.625.This ideal is based off of D.Morgans pressure recovery post.
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Re: 1.625 header rule

Postby ProPower engines » Sat Dec 03, 2011 7:29 pm

What carb are you restricted to using?
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Re: 1.625 header rule

Postby Unkl Ian » Sun Dec 04, 2011 12:04 am

A step on the exhaust can reduce reversion.
But the difference isn't likely to be night and day.

Have you tested different collectors ?
Just because you never studied the Laws of Physics,
doesn't mean they won't try to kick your ass.
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Re: 1.625 header rule

Postby RCJ » Sun Dec 04, 2011 9:04 am

Any carb is legal.Using a 750 quickfuel have a 950 APD but, have never tried it on this motor.I've always dyno the motor with dyno headers that are 1 3/4.This year I'm build my own headers and will dyno with them.The way the old headers set in the car you couldn't put very much collector on them.The new headers should solve that problem.
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Re: 1.625 header rule

Postby randy331 » Mon Dec 05, 2011 10:28 pm

RCJ wrote:I could change cam timing but, I'm really trying to think outside the box and get an edge on the competition.
Expanding the pipe at the head then reducing the size.Wouldn't that create a low pressure area when the gases speed up in the smaller pipe?
Making the pipe the same size as the exhaust port then a smooth transition to 1.625.This ideal is based off of D.Morgans pressure recovery post.


If the area is small, increases in size, then gets smaller again, there will be no pressure recovery at that point. There will just be a change in the form of energy from one form to another and then back. To recover pressure the area must continue increasing in size at a controlled rate.

Since you are building new headers I would suggest making them come off the heads straight as far as possible and at a slight up-ward angle and then nice sweeping bends. If you can make them exit up and a little away from the center of the bore also, that would be good too, but you can't do both pipes on the center 2 cylinders that way. This has always shown to flow the best on the flow bench on the 23* sbc ex ports and I see no reason to beleive it would like something different with faster moving ex gasses flowing through the ports/pipes, atleast as far flow goes.

I'd be suprised if collectors help power at and above 5900 rpm. From what I've seen collectors have more affect below peak tq than anywhere and I'm guessing your making peak tq at about 5000 rpm.

If you want to help power above peak tq. you need to help ve not fall off as fast, and I'm betting the stock vortec heads are the limit.

Can you redo the valve job?
A bigger valve?
Rocker arms?

I'd agree with the suggestion of backing the cam up some. I've seen that help power past peak tq several times.

Randy
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Re: 1.625 header rule

Postby RCJ » Tue Dec 06, 2011 9:52 pm

2012 Rules came out today Engine quest 906 vortec are allowed.I been running GM 906 vortecs with 2.02/1.60,crower shaft 1.5 rockers.
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