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Discussion Starter · #1 ·
:welcome:

Hi guys. I know this may have been discussed in detail elsewhere but I cannot find what I'm looking for. I am looking to install my engine this weekend but the exhaust is one of the last pieces. My question is about tube diameter. I already purchased my headers( 2" primaries
3" collectors) but didn't realize there was so much to header selection. My engine is a 454 bored .030 over; MSD ignition; edel performer 2 intake; edel 750 carb. I have been given conflicting opinions about these headers with my applications. Are 2" primaries too much? Should I go ahead and run 3" all the way out the back or reduce them some? Opinions please.
 

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I think you're about 2 tube sizes too large. Something like a 1-3/4" x 40" primary tube with a 3" collector. Maintain the collector diameter all the way to the secondary junction. After the secondary junction you can reduce the pipe size to 2-1/2" for the rest of the way.
 

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Bll Curtis

I recently read an extensive article on header selection @ Summit's exhaust web site. I recall it spoke directly to big block choices as long as you know package/clearance limitations.
Long runs vs shorties may be of interest to you.
 

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Discussion Starter · #4 ·
I got mine from summit. I chose them using their drop down selector to find one that fit my car with my engine and that was the only choice they had. I almost went with shorties but figured the custom fit app. would be best. Also just figured bigger primaries = more flow = more fun. Gotta excuse my green. Is this the kinda thing thats gonna bog me. Will be running 3.73 posi, 2500 stall. Basically a street machine that will see the track may 3 times a year.
 

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One of the largest errors street enthusiasts make is in running too large of a primary pipe, and too large of a collector. For example, NHRA and IHRA Stock teams using Burns' headers in H/SA in traditional small-block powered musclecars are running 1.5-inch diameter primary pipes- much smaller than many street machines are trying to use.

http://www.popularhotrodding.com/tech/0310phr_jack_burns_exhaust_manifold_header_tech/

If we were talking about intake runners here, most guys would have no problem understanding that a smaller intake runner works better on a moderate performance engine. In the case of a BBC, a stock 049 head runs about 280cc's on the intake port. A 33% increase in area would bring this up to 372cc's. If I posted a piece on how I was going to use 372cc heads on my mild 454, you can bet there would be more than one reply saying it's way too large. It works the same on the exhaust side, a smaller diameter primary of the proper length will increase the scavenging in your engine resulting in increased efficiency and power.
In most professional grade computer engine analyzers there is a calculation called something like Overlap%VE, which means what percent of the volumetric efficiency is contributed to the use of the overlap period. Overlap is used for scavenging the cylinder, applying the negative pressure wave at the port to suck the remaining exhaust gases out of the cylinder and initiate the filling of the cylinder even before the piston has started down the bore. If the scavenging wave is weak because the tubes are too large, your performance will suffer.
 
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