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Discussion Starter #1
Not sure if this topic has been discussed before (couldn't find it), but here goes.

I'm considering getting LT headers, but don't want to screw up my torque curve too much since my stang is a DD. So my question is does anyone have dyno data showing what dimensions on LT headers give the most low to mid range torque/hp gains? In other words, which tube diameter gets the exhaust gases to peak velocity in the least amount of time without causing excess back pressure?
 

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Well it almost kinda defeats the purpose of getting headers for the mere fact that most headers are designed to move the curve higher and help out with the top end where the exhaust gases are greatest and the exhaust pulses are shortest. But generally, gains are going to be made across the board with the major benefits up high.

Anyways, if you are looking to retain low end power you should look at headers with a smaller diameter primaries. This will increase velocity at low RPM's but may be a hinderence at the higher engine speeds. Also look at if anybody makes a tri-Y design for our cars. Back in the old hot rodding days these were popular because they were supposed to help down low for the street. I don't have any empirical data to support this, just what I've been led to understand.
 

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1 & 5/8 " for N/A 1 & 3/4 " for FI
 

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Discussion Starter #4
thanks guys - appreciate the input. I was doing some research and found this formula, play around with it and let me know if the numbers actually match up to real-life experience or dyno data.


Peak torque rpm = Primary pipe area x 88,200 / displacement of one cylinder. Using this with the data from FLBEAST, I came up with the following:

With 1 5/8 headers, peak torque came at 4,708 RPMs and with 1 3/4 headers, peak torque came at 5,500 RPMs.

Here's the article:

Header Basics - How Headers Contribute to Horsepower - Car Craft Magazine

Does anyone know the dimensions of OEM exhaust manifolds? Would be interesting to run some comparison numbers...
 

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gtscrewd
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thanks guys - appreciate the input. I was doing some research and found this formula, play around with it and let me know if the numbers actually match up to real-life experience or dyno data.


Peak torque rpm = Primary pipe area x 88,200 / displacement of one cylinder. Using this with the data from FLBEAST, I came up with the following:

With 1 5/8 headers, peak torque came at 4,708 RPMs and with 1 3/4 headers, peak torque came at 5,500 RPMs.

Here's the article:

Header Basics - How Headers Contribute to Horsepower - Car Craft Magazine

Does anyone know the dimensions of OEM exhaust manifolds? Would be interesting to run some comparison numbers...
that would be interesting:shiftyeyes
 

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thanks guys - appreciate the input. I was doing some research and found this formula, play around with it and let me know if the numbers actually match up to real-life experience or dyno data.


Peak torque rpm = Primary pipe area x 88,200 / displacement of one cylinder. Using this with the data from FLBEAST, I came up with the following:

With 1 5/8 headers, peak torque came at 4,708 RPMs and with 1 3/4 headers, peak torque came at 5,500 RPMs.

Here's the article:

Header Basics - How Headers Contribute to Horsepower - Car Craft Magazine

Does anyone know the dimensions of OEM exhaust manifolds? Would be interesting to run some comparison numbers...

The iron manifolds are 1.5" with a 2-1/4" collector. Headers will reduce back pressure.

The most effective header design will have equal length tubes tuned so the exhaust pulses create a vacuum effect to pull the next pulse down the header and prevent exhaust pulses from interfering with each other in the collector. That is the scavenge effect.

From what I've seen, there's not enough difference between a equal length LT vs an the unequal length LT to choose 1 over the other. The $400 JBA's will work as well as the $1400 ARH's.
 

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The iron manifolds are 1.5" with a 2-1/4" collector. Headers will reduce back pressure.

The most effective header design will have equal length tubes tuned so the exhaust pulses create a vacuum effect to pull the next pulse down the header and prevent exhaust pulses from interfering with each other in the collector. That is the scavenge effect.

From what I've seen, there's not enough difference between a equal length LT vs an the unequal length LT to choose 1 over the other. The $400 JBA's will work as well as the $1400 ARH's.
Correct. I have JBA's and I have absolutely no complaints with them.
 
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