AMC Header Test Results

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We have just completed a ABC comparison with ported Free Flow manifolds, Edelbrock Shotry headers #65873 and 1 5/8" long tube Hedmand Headers. The mill is a street 401 with dual quad 500 cfm Edelbrock carbs. on a Offy intake. It has '70 heads and the compression ratio is 10.2:1. Minimal porting was done, just smoothed out the combustion chambers and exhaust ports. The cam is a Isky 280HL. 224/224 @.050, .490 lift, 108 LS. The Free Flow manifolds were modified by grinding out the smog tube bosses and contouring the runner. A 2' section of 2.5" O.D. exhaust pipe was used with both the manifolds and Shorty headers. The long tube headers are for a CJ Jeep application.

Results: (I will post up actual data when I get it)
Free Flow Manifolds (ported)::::: 366.2 Hp @5050 401 #/ft Torque @ 3800
Edelbrock Shorty Headers:::::::: 368.7 Hp @5250 411 #/ft Torque @ 4300
Hedmand Long Tube Headers::::: 382.0 Hp @5050 430 #/ft Torque @ 4300



These are the videos if you want to hear it run............

Ported Free Flow Manifolds

Edelbrock Shorty Headers

Hedmand Long Tube Headers

[The Colonel]

Thanks for sharing!

[fulsizjeep]

Thanks for sharing this!

For those scoffers of the Hedman long tube headers:
Take note of the loss of torque with these compared to the other two.
Didn't see it it did ya?

[MonsterZ]

Exactly why I ran them on my chebbies....

[mud89]

Thanks for sharing !
Is it Hedmand or Hedmond ?
I don't know Hedmond headers

[SC/397]

They become Hedmond after I fix the ports on them...

[The Colonel]

For those scoffers of the Hedman long tube headers:
Take note of the loss of torque with these compared to the other two.
Didn't see it it did ya?

Kinda makes you feel bad for those who bought the shorties....

[Ristow]

WAIT A MINUTE!! how can this be?? i read headers kill torque and don't do anything under 6000 rpm,right here on this forum!!!



yup,i'll pass on the edelbrocks and keep my hedmans.

Kinda makes you feel bad for those who bought the shorties....

LOL! like i've said before. if you're gonna run headers why not get some power out of the deal too?

[SC/397]

Yea, I have 2 sets of those shorty's new in the box. Well,...... one set is slightly "used".. I would like to work with them a little more. Just by looking at them they restrict the flow down to 2.5" I.D. in a very short distance. I would like to experiment with them by cutting the tiny collectors off and running a 3" tube off of them. At least a foot long maybe two if I could fit them in a vehicle. Here is the two different styles side by side.


I made a set for a AMC 327 engine so, I know that it takes a BUNCH of time. I would really like to develop a pair of "medium" length tube headers that would be a one size fits all for AMC street cars and Jeeps but GEEZE it is a lot of work...

[Billygoat]

I'd like to see the full curve - cause who runs 4300rpm
or dual quads for that matter. - I know street mill does not mean a DD

Just saying peak numbers are cool, and great for racers, but I suspect the 2000-2500 rpm numbers would probably show very little difference.

[SC/397]

I am looking at the curves. At 3000 rpm's the manifolds and shorty headers made about the same torque at about 395#/ft. The torque started going up at about 3200 with the shortys and the manifolds stayed the same. We called the torque curve on the manifolds a "torque plateau". At 3500 the torque was 420 #/ft with the long tube headers. I honestly believe that the dual quads didn't add any horsepower or torque. In fact, I think that it hurt it. It would be interesting to do a bunch of intake and carb swaps too but I wanted to keep the variables at a minimum. I will post up the actual data when I get it.

[Ghinmi]

This is really interesting Rick. Those stock manifolds really picked up with the port work. I lost a ton of power with unported manifolds vs Edelbrock shortys. Looks like I'll be ditching the shortys for manifolds or long tubes. Thanks for putting this to the test!

[Billygoat]

I am looking at the curves. At 3000 rpm's the manifolds and shorty headers made about the same torque at about 395#/ft.

At that does prove what I was getting at the manifolds produced 98.5% of there max torque in the normal daily use range - up to 3000rpm
I suspected the long tube headers will have similar numbers.

It does make we want to get my manifolds ported!

good job on the test - thanks!

[Jeepguy77]

This is all good data, I actually do rev my engine past 3000 rpm sometimes so yes it does help me. But I'm also a 20 year old hotrodder with a heavy foot and love to punch it when getting on the highways.

[JeepsAndGuns]

VERY interested in the full hp/torque curves too.
I too have read lots of times on this site about the stock manifolds being the best for torque, thats the main reason I am still running them. These numbers seem to disagree with that. I have done the same porting to my stock manifolds.
If you dont have the full curves, do you happen to have the torque numbers for the ported manifolds at 4300 rpm?

I would also like to see the numbers for each one at like 1500, 2000, 2500, and 3000 rpm's. Would love to see how they compare at the normal driving rpm range.