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#1 |
Senior Member
![]() Join Date: Mar 2001
Location: Cedar Park, TX
Posts: 686
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Headers - How Important is Primary Size?
How much of a difference will it make if one installs
1-5/8" vs 1-3/4" primary full lenght headers. Let me add the part numbers that I am questioning is the hedman elite series HED-69890 vs HED-69088. ------------------------------------------ This would be for a streetable driver, not a race truck. TIA...
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71 Chevy C-10 SWB Fleetside RamJet-350/4L60e & Compushift/3.73Posi See it at www.prismnet.com/~grzanich Last edited by BubbaGreen; 10-15-2005 at 11:28 AM. |
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#2 |
Registered User
Join Date: Sep 2005
Location: San Angelo or Eufaula
Posts: 301
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primary size is very important, too big, can kill low end torque, too small can kill upper rpm hp. With a tbi 350, go with the 1 5/8".
Kirk Last edited by cst70rocket; 10-15-2005 at 11:57 AM. |
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#3 |
Senior Member
![]() Join Date: Mar 2001
Location: Cedar Park, TX
Posts: 686
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Guess I should have stated, this is for use with a GM Crate motor RAMJET-350 TPI.
The included manual specifies 1-3/4" Primary dual exhaust w/ H-Pipe. The price difference between header models is approx 40-50 bucks.
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71 Chevy C-10 SWB Fleetside RamJet-350/4L60e & Compushift/3.73Posi See it at www.prismnet.com/~grzanich |
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#4 |
Active Member
![]() Join Date: Jun 2002
Location: L.A. Lower Alabama
Posts: 453
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Re: Headers - How Important is Primary Size?
Try this link lots of info on building headers and what different size primaries will get you.
http://www.headersbyed.com/index.htm
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1969 C10 350 3spd 1995 GMC 3500 XC 350 dually When Thomas Edison worked late into the night on the electric light, he had to do it by gas lamp or candle. I'm sure it made the work seem that much more urgent. George Carlin |
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#5 |
The LuvShack Garage
Join Date: Jan 2004
Location: Maple Grove, TN (West Side)
Posts: 30,477
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Re: Headers - How Important is Primary Size?
I had very limited choices on this for my rig, on a 4wd everything reasonable is
5/8 unless you want custom or very expensive headers, to rich for my blood ![]()
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Owner/Op: "TN Classic Transport Carriers" The Toy: "Square Vette" 72 Hybrid Blazer Toy Barn: "LuvShack" 40 x 60 x 20 Shop Tow Piggy:"Maddy" 88 Silverado 3500 Hauler: "Feathers" 14 Aluma 8218T |
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#6 |
Registered User
Join Date: Nov 2003
Location: Alexandria, VA
Posts: 1,534
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Re: Headers - How Important is Primary Size?
Man Zeke, what a informative site. I didn't know and I'm sure many others don't know how much potential power can be lost (read that as not gained) by bolting on a set of their favorite headers.
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'72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction. ![]() ![]() ![]() |
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#7 | |
Smell that burnin' rubber
Join Date: Sep 2000
Location: Ontario
Posts: 171
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Re: Headers - How Important is Primary Size?
Bubba, the header pipe size dictates max flow rate, velocity, and to a certain degree scavenging. Normally SBC header pipe of 1 5/8 is ideal. 1 3/4 is appropriate with a radiacal SBC making major HP #s. The Ramjet stock cam is relatively mild and as CST said, the larger pipe size will kill your low end torque.
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#8 |
Registered User
Join Date: Mar 2001
Location: Moore, Ok
Posts: 1,149
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Re: Headers - How Important is Primary Size?
http://www.headerdesign.com/index.asp is a great site for header and exhaust information. I think you'll find that the 1 5/8 is a better choice than the 1 3/4 for your application. To bad they don't make headers with longer primarys.
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72 SWB parts and pieces Oklahoma |
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#9 |
Senior Member
![]() Join Date: Mar 2001
Location: Cedar Park, TX
Posts: 686
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Re: Headers - How Important is Primary Size?
According to the ship along ramjet-350 manual.....it makes reference to all testing and tuning using 1-3/4 primary into 3" collector using 2-1/2" exhausting tubing w/ an H-Crossover pipe.
But, I am thinking if I install the 1-3/4 inch primary header, that I will suffer the low end torque. I do plan on going with 2-1/2 inch exhaust. Havent had time to check out the posted link, but will do so later.
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71 Chevy C-10 SWB Fleetside RamJet-350/4L60e & Compushift/3.73Posi See it at www.prismnet.com/~grzanich |
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#10 |
Old Skool Club
![]() Join Date: Jun 2001
Location: Benton, AR "The Heart of Arkansas"
Posts: 10,880
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Re: Headers - How Important is Primary Size?
I haven't seen it mentioned, yet, but remember that an internal combustion engine is very much an air compressor. With that in mind, you have to concern yourself with the engines' ability to process the incoming air and that means also exhausting it. Starving it for air, will limit its' efficiency. To use a too-restrictive exhaust will also limit the efficiency. So, it is with those ideas in mind that the engineers and test folks test what works and what doesn't. While their tests were done with the larger of the two sizes of tubing, it doesn't mean that the engine won't function with the lesser size. Going for the larger diameter will allow more air to exit the engine, specifically at higher rpm's. However, like stated earlier, the smaller diameter tubing will aid in low-end torque, which is what you feel from the "git-go".
The H-pipe balance tube, is designed to even out the pulses and help create a scavenging effect, causing the exhaust system to effectively create a vacuum effect from one side, to the other. The only problem for my truck, is that the optimal place for the balance tube, is directly beneath the pan on my transmission. So, I am running without one. The balance of the exhaust system also will affect performance, but there has to be some back pressure in it, for optimal street efficiency. How much? Good question. I've got a 2.5-inch system, from the headers, to the 40-series Flowmasters, then 2.25-inch from the mufflers.
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Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was. |
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#11 | |
Registered User
Join Date: Nov 2003
Location: Alexandria, VA
Posts: 1,534
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Re: Headers - How Important is Primary Size?
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'72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction. ![]() ![]() ![]() |
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