Best Header Size?
Thread Starter
Racer
Joined: Mar 2003
Posts: 261
Likes: 0
From: Philadelphia PA
I agree, but MTI only carries the 1 7/8" version and Nick at Kooks stated there are great gains to be had on a stock sized motor with these. I'm still thinking about going with the 1 3/4", but would love to see a before and after graph with the 1 7/8". 
Melting Slicks
Joined: Dec 2004
Posts: 2,322
Likes: 2
From: New York NY
Cruise-In VI Veteran
St. Jude Donor '05
But I think your decision is contingent upon future mods. If you plan to install a blower at some point/forced induction, the 17/8 are probably for you. Other wise the 13/4 should serve most other applications
Melting Slicks
Joined: May 2003
Posts: 2,840
Likes: 301
From: Bonita CA
Go with the 1 3/4" DynaTechs, they are also SS so you don't have to coat them. The steel ones rust out quick, from the inside out, if you don't coat them. With most applications, the 1 3/4 will give you better bottom end. There are some complex formulas to calibrate optimum header size but the bottom line is that the 1 7/8 will help at the higher RPMs. Depends on where you want the power and a number of other factors. For most of us street guys, 1 3/4" is best. Bigger is not better when it comers to headers. Most experts will tell you to err on the smaller side. Car Craft did a nice article back in Dec. 2003 on how to properly size headers for application. What I told you was their bottom line.
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Supporting Vendor
Joined: Jan 2000
Posts: 5,683
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From: TX
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St. Jude Contributor '04
Please, dont buy anything bigger than 1 3/4 for stock displacement applications. You wont see much of a gain if any, going 1 7/8.
I have been there and done that.
Thanks,
Nate
I have been there and done that.
Thanks,
Nate
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Team Owner
Joined: Feb 2001
Posts: 27,217
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From: Short Hills, NJ
Safety Car
Joined: Oct 2001
Posts: 3,504
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From: Insert Wittty Comment here
1 7/8" is too big for almost any 346 unless you turn way more RPM than any Hyd. motor can turn. Its a pretty simple fact...
Here is the math for tube sizing...
Header pipe length (in inches) = ((850*(360-EVO))/RPM – 3
Header diameter (in inches) = ((cylinder. disp. * 16.38 / ((hdr len + 3) * 25))) * 2.1
Exhaust Valve Opens - EVO
You'll find on most avg 346" motors 31-32" primaries and ~1.7x tube size is the math you come up with...
Here is the math for tube sizing...
Header pipe length (in inches) = ((850*(360-EVO))/RPM – 3
Header diameter (in inches) = ((cylinder. disp. * 16.38 / ((hdr len + 3) * 25))) * 2.1
Exhaust Valve Opens - EVO
You'll find on most avg 346" motors 31-32" primaries and ~1.7x tube size is the math you come up with...
