Edelbrock heads Vs. Stock 291-c's the unequivocal truth

[jeepsr4ever]

The reason we found for the loss in lift above .500 was that it just gets too turbulant. It was found the shape of the port is not smooth and causes this turbulance. We did not use a exhaust spud or stub to simulate a header. After porting we couldl use a exhaust stub to simulate a set of headman headers and repost the numbers. Exhaust stub for the exhaust eh? Hmm I will see what our guy here has to say about that.

[82Waggy]

Part of the turbulence problem could very well be attributed to the lack of a stub tube on the exhaust or an inlet fairing on the intake port.

The exhaust port is not designed to simply dump out of the head and will not flow properly without a manifold.

The intake is designed to work with a manifold as well - simply trying to pull air in through the hard square edge of the head will not do. For the heads I did the other day we faired the inlet with modeling clay - making a shape around the port similar to the shape of a jet engine nacelle.

These things make a HUGE difference in the results.

[jeep_man_401]

These are the flow numbers I got on my Indy heads after I reworked them...hoping I didn't lower the flow. I think I did alright just by going by feel and eye.... (bottom row is the flow )

My cam's max lift is .560 anyway. And the cam was made going by the catalogs flow numbers...maybe next time I will use a roller with these numbers.





Out of the catalog...

[jeepsr4ever]

Interesting numbers.

On Kens test with the stub I wonder about the stub size for the dogleg. As you can see the AMC blueprint and actualy dogleg vary quite a bit


The AMC dogleg print (in black), the actual dogleg after machining (stock (in red)) and a port from Hedman headers (dotted in green). Now our test was done with a 1 7/8 hole on the exhaust which might account for the lower flow and we used a port matched stub on the intake. I will use a hedman header stub on the exhaust next time but I believe it will hurt flow. I am hoping to get a set of 1 7/8 thorleys to use one port as a stub.

We are working on header flanges for the AMC dogleg heads and header/intake gaskets as well for proper port matching and custom header building.

[AMX69PHATTY]

No wonder I had to do so much grinding, chamfering, and flaring
to match the ports on my cheapy headers to match the gaskets.
Especially in the DogLeg area.
Header folks probaly hate the DogLeg profile.
Have to use some kind of a swaging tool on the tubes I guess.
But whent they welded'em to the flange plate
they almost eliminated the dogleg shape with the weld bead.

[jeep_man_401]

{We are working on header flanges for the AMC dogleg heads and header/intake gaskets as well for proper port matching and custom header building.}

That would help, as the supply of good headers is limited. I really need a set of 1 7/8 on my 401...the Headman headers are crap.

[82Waggy]

Slightly oversized on the header flange wont hurt anything.

Verses no stub at all, you will be amazed at what a difference even a slightly undersized stub will make. Even a round tube of a diameter that encompasses the port will improve flow over no stub at all.

[Holeshot]

Thanks for the great thread, guys!!!

[Holeshot]

Hooker "Super Comp" headers come in 1-7/8" but are quite costly. Hedman supposedly has big-tube stepped race headers for AMC but I've never been able to verify that they are in fact available...

Hedman:
* HED-95100-6-E2 Husler 2" prim, 3.5" coll., Coated, Stepped CALL
* HED-98310 68~80 AMC 1-5/8" primary 3" collector $ 105.95
* HED-98310-6 same as above, with ceramic coating $ 325.39
* HED-99190 Jeep CJ fenderwell exit, 1-3/4" 3" $ 105.95
* HED-99196 same as above, with ceramic coating $ 325.39
* HED-99200 Jeep CJ 72~86 1-3/4" 3" collector $ 105.95
* HED-99200-6 Same as above, with ceramic coating $ 289.95
* HED-99240 Cherokee J10 Waggoneer 74~79 1-3/4" 3" col $ 105.95
* HED-99250 Cherokee J10 Waggoneer 80~83 1-3/4" 3" col $ 105.95
* HED-21107 3 in. dia. 3-bolt to 3 in. outlet, with O2 reducers $ 15.69
----------------------------------------
Hooker:
* HOK-10979 weld-on oxygen sensor fitting $ 11.69
* HOK-11037 3-1/2" coll to 3 1/2" pipe 3-bolt O2 reducer $ 23.95
* HOK-7103 SuperComp 68~74 1-7/8" prim 3-1/2" coll $ 385.95
* HOK-7103-1 Same as above, ceramic coated $ 565.95
* HOK-7105 SuperComp 1-3/4" prim 3" coll $ 299.95
* HOK-7901 Comp 1-5/8" prim 3" coll auto on floor only $ 141.95

[Holeshot]