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2 1/8" would probably be "better" assuming you want max power.

2" will work OK, and especially if you'd like to make power lower in the rpm range
 

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Discussion Starter #3
Hey CHilly! But you think that 2 1/8 would be absolutely better? It is going into my 2800 lbs FOx Mustang with 5 speed.....so I really dont need TOO much low rpm power....
 

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At that level, I'd definitely think a 2 1/8" would be optimal...

Many of your decent street/strip 410ci type small block strokers run 2" headers...the 2 1/8" is perfect for a big stroker presumably turning a little rpm to make those kind of numbers. Light car, stick...I'd definitely go with the big tubes.
 

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Headers

You can certainly make 750fwhp through 2" primaries. I've tuned blown small block Mustangs making more than that through 1 3/4 primaries. It can be done.

As far as would bigger be better? Almost always, as far as horsepower is concerned...but I'd be willing to bet the difference between 2" and 2.125" on a 750fwhp engine would be less than 20fwhp holding everything else constant. It certainly isn't badly choked with 2" primaries.

How many times have you seen a car produce 300fwhp through dual 2" exhaust? I've seen it more times than I can count. You're talking about 8 2" pipes. Surely you can make 2.5X that much power through 4X as much flow potential.

Byron
 

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I gained 30 hp on my 512 motor going from 2.125 to 2.250 primarys.

It lost about 10 ft lbs of trq. thou. If its N/A 2.250 would be best IMO.
 

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Since you didn't specify what cylinder head you have, only hp figures I would have to say to measure the longest side of the exhaust port opening ( flange side ) and stay within a 1/16 to 1/8 max above that number.
example: if the longest side of the exhaust opening is 2" then you would want to run a 2-1/8 primary pipe. That way you will have a 1/16 on both sides of the longest side of the port opening. The primary pipe should be nothing more than an extension of the port opening, This will promote better exhaust gas flow. Same as a porting guy flowing your heads with an extension pipe to make the numbers look better.
Just my humble opinion.
 

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If you're buying headers for the first time with this application I'd say definately go with the 2 1.8" primary headers.
If you already HAVE 2" primary tube headers I'd say the possible minimal power gain is not woth the expense for the larger header and just have a 4" collector installed on to the present 2" headers.
 

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Where did you get those headers! Do they fit a fox body mustang?
 

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Discussion Starter #12
Thanks Randy for the reply, I am buying my first set of headers, so I''l go with the 2 1/8"....Those headers on the pic are Hooker 6201-1HKR, with 2 1/8 primaries and ceramic coated....
 

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looks like they are for the old mustangs..crud! I need that same header for a fox mustang
 

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Has anyone ever used those on a 1969 mustang? The reference shows they are for a fairlane.
 

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Discussion Starter #15
Sorry ....My mistake....the fox Part# is HOK-6224-1HKR, and are 2" primaries.........the other ones I mentioned before are for older Mustangs.....

These are the headers for Fox Mustangs with 385 Big Block

 
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