header performance - Chevelle Tech
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post #1 of 8 (permalink) Old Oct 11th, 18, 5:24 PM Thread Starter
 
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header performance

I currently have some mid 90's Hookersupercomps 2 1/8 primaries with 3.5" collectors that need replacing. I have found a deal on a set of darkside hookersupercomps but they are only 2" primaries and 3.5" collectors. I have dart 325 heads and am wondering if going to the smaller tube is going to hinder performance by much? Any idea or is it not going to matter?
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post #2 of 8 (permalink) Old Oct 11th, 18, 6:18 PM
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Re: header performance

I have a friend (mino65 here on TC) that runs high 9's @135+ MPH with a pump gas oval port 496 with those "only" 2 inch primary/3.5 inch collector Hookers.
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post #3 of 8 (permalink) Old Oct 11th, 18, 7:54 PM
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Bill R
 
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Re: header performance

As stated above, there is a very good possibility that the 2" primary tube headers will out-perform the 2.125" primary tubes that you are now using. Bigger isn't always better when it comes to header tube diameter.
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post #4 of 8 (permalink) Old Oct 11th, 18, 9:20 PM
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Gary
 
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Re: header performance

we dont have any information to give you a header recommendation. how big is the engine? what cam,whats the intended useage how much compression etc etc. i will tell you that i have 2.125 headers on my 505 inch racecar that makes 860 hp and its not faster with 2.25 headers.
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post #5 of 8 (permalink) Old Oct 12th, 18, 12:35 PM
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Mike
 
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Re: header performance

Quote:
Originally Posted by gnicholson View Post
we dont have any information to give you a header recommendation. how big is the engine? what cam,whats the intended useage how much compression etc etc. i will tell you that i have 2.125 headers on my 505 inch racecar that makes 860 hp and its not faster with 2.25 headers.
depends on how many cubic inches and how tight you are turning it. there is a point where they just won't flow any more exaust.
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post #6 of 8 (permalink) Old Oct 13th, 18, 12:35 PM
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Re: header performance

I'm only running a weenie little SBC, but it made 915 HP @7600 RPM on the dyno with 2" to 2-1/8" step headers. I'm running 2" x 3.5" headers in the car. The corrected chassis dyno and ET/MPH in the 1/8th mile seem to indicate high 880 HP. So as installed vs. dyno could be losing up to 30 HP.

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post #7 of 8 (permalink) Old Oct 19th, 18, 4:29 AM
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Tim T
 
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Re: header performance

Hot rod magazine tested 5 different size header tubes on a 700hp 540ci. On there combo the 2" and 2.125" were almost the same. Maybe 3or 4 horse on the very top end (6500) Very interesting. They added 18" collector extensions and picked up like 30ftlbs. of tq. Low to mid range. I believe every size had significant gains with extentions. Much more then primary tube size. Check it out. Google it. (Hot rod header test) .
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post #8 of 8 (permalink) Old Oct 19th, 18, 9:04 AM
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Lew
 
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Re: header performance

The article that the guy mentions above was great as they tested the headers you are talking about. There was no tq difference or minimal between the 2 inch and 2 1/8 and it was like a 9 hp difference up top. If you are running an exhaust probably wont matter. Also what size engine do you have, as this was a 540 they tested. I would say go with 2 inch as they will fit better and not worth the trouble. Also not sure what year Chevelle you have, but going to 2 1/8 means a pesky tube has to go around a frame (1964-1967) to fit (unless you do Lemons). Base on the article the breakpoint is like 700-725 hp for the 2 1/8 but it was not like a huge difference at that power level.
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