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The perfect header for the smaller big block

Old 12-01-2018, 10:01 AM
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Default The perfect header for the smaller big block

I know and understand this is a open question, but I'm trying to limit the answers for 454 to 502 engines. So my question is what size primary's and what length would be your choice and why?

Thanks in advance!
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Old 12-01-2018, 11:15 AM
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Originally Posted by Camalot
I know and understand this is a open question, but I'm trying to limit the answers for 454 to 502 engines. So my question is what size primary's and what length would be your choice and why?

Thanks in advance!


Nuff said........
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Old 12-01-2018, 11:28 AM
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Too many variables. Cam, induction, rpm range. All that matters more than ci
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Old 12-01-2018, 01:55 PM
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Originally Posted by Crude Intentions
Too many variables. Cam, induction, rpm range. All that matters more than ci
I'll fill out that info once I get it all in my hand.
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Old 12-01-2018, 02:18 PM
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Yup. The Diamond Performace/KE Thunder-N-Lightning have 1 3/4"x 34" pirmary runners. Collectors are 4" and you make the collector length.Most marine 502's-540's want 18-20"collector lengths.
http://www.diamondperformanceparts.c...age=1&featured

Here is Pipemax on a 502 i entered with a Crane 741 cam and 5800rpm max rpmpower.

--- Single Primary Pipe Specs --- for 502.176 CID from 3800 to 6300 RPM
Diameter= 1.899 to 2.024 Length= 33.7 to 36.7 inches long

--- 2-Step Primary Pipe Specs ---
1st Dia. inches= 1.899 Length= 16.9 to 18.4
2nd Dia. inches= 2.024 Length= 16.9 to 18.4
--- 3-Step Primary Pipe Specs ---
1st Dia. inches= 1.899 Length= 16.9 to 18.4
2nd Dia. inches= 2.024 Length= 8.4 to 9.2
3rd Dia. inches= 2.149 Length= 8.4 to 9.2

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter= 3.466 to 3.716 Tuned Lengths= 19.4 best and also 9.7 or 38.8


--- Header Collector Specs (Megaphone or Diffuser Cone Shape) ---
Diameter= 2.966 taper to 3.966 Megaphone/Diffuser Length= 19.4 inches

Best HP/TQ Tuned Collector Lengths= 19.4 , 38.8 , 77.6 , 155.2 inches long

Worst HP/TQ Loss Collector Lengths= 29.1 , 58.2 , 116.4 , 232.8 inches long
Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness

---- Primary Pipe's Harmonics ----
1st Harmonic = 149.4 inches long ... typically never used
2nd Harmonic = 56.5 inches long ... longest recommended
3rd Harmonic = 33.7 inches long ... highly recommended , best Torque Curve
4th Harmonic = 23.4 inches long ... shortest recommended
5th Harmonic = 17.5 inches long ... typically never used
6th Harmonic = 13.8 inches long ... typically never used
7th Harmonic = 11.1 inches long ... typically never used
8th Harmonic = 9.2 inches long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 155.2 inches long ... longest with Mufflers and TailPipes
Note: Worst = 116.4 inches long for HP/TQ Loss
2nd Harmonic = 77.6 inches long ... longest recommended with Mufflers
Note: Worst = 58.2 inches long for HP/TQ Loss
3rd Harmonic = 38.8 inches long ... more bottom-end Torque
Note: Worst = 29.1 inches long for HP/TQ Loss
4th Harmonic = 19.4 inches long ... highly recommended , best Torque Curve
5th Harmonic = 9.7 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4.9 inches long ... reduced Torque , not recommended

Last edited by SB; 12-01-2018 at 02:21 PM.
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Old 12-01-2018, 04:17 PM
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Thanks SB that's just what I'm looking for, most of my adult life I have designed and built two stroke engines and pipes. Mostly the pipes as not many people can do that. This is my first four stroke where I want to build my own.
I'm close to what you have posted but I'm coming up with 1 7/8 but the same length as you.

ive used ENGMOD 2TFor years but now playing with ENGMOD 4T and struggling with what the EGT should be. I have no data how a water cooled exhaust behaves with regards to EGT so I'm kinda pissing in the wind lol. Thanks again.
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Old 12-10-2018, 09:38 AM
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Originally Posted by Camalot
I know and understand this is a open question, but I'm trying to limit the answers for 454 to 502 engines. So my question is what size primary's and what length would be your choice and why?

Thanks in advance!
If your engines as mostly stock, donít look for much or anything additional on the speedometer.
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