BIG BLOCK JAMO

should i expect any problems installing 390 hp oval port intake manifold on my 425 hp square port heads?? will they seal properly? which gasket should i use? i know this sounds stupid but i have my reasons.. thanks in advance;:f lag:

MiguelsC2

Deja Vu man! Didn't you run this thread a few days ago?

snydes

I believe that thread was oval port on a 4 bolt block...

While certainly not ideal, I believe it should function. I do know of a car that was running a square port intake on oval port heads and it ran fine.

BADBIRDCAGE

Not going to work. Square port manifold on oval port heads works using square port intake gaskets. Heads provide the sealing surface.

Oval port manifold will not seal on square port heads. Ports on heads are too large to seal with oval port intake gaskets.

DZAUTO

THAT IS EXACTLY CORRECT!!!!!!!!!!!!
Read and heed.

Tom Parsons

midyearvette

i don't know if they are still available but mr gasket made a "ported" intake gasket for an oval head bb chevy that did work (cover the square port head) years ago........

Paul67

I know this an old thread, but I could use some feedback from those using Square manifold with Oval heads.

Specfically, I thinking of a ZZ454 or other Oval Headed crate motor/long block mated with my 3x2 intake # 3894374.

I know the post here and other forums indicate it will work, my question is will it perform close to an oval to oval or rect. to rect. OR will it work but not perform great?

Thanks

AZDoug

Rect manifold on oval heads will work fine, except, you may lose vacuum signal to carb causing low RPM hesitation/bog problems due to the larger manifold cross section, which can generally be overcome with accel pump tweaks or idle mix adjustments, but since you are just running off one carb at low RPM, this may not be an issue. I don't think you will see enough RPM to get serious degradation of flow at higher RPM.

My recollections of this from many years ago, may have been more of a cam mismatch for the motor than head / manifold match problem.

Doug

midyearvette

i have used the square intake on oval heads with square gaskets and it works fine
i do not have any dyno numbers for data as how much it may or may not hurt performance
still smoked the tires from a roll on all the cars i have done this to.....

Joe Sprintbros

Yes, it will operate fine, I used #163 rect intake on oval #049 heads on 427 bracket car for years. In this case, you use the rect port intake GASKET to seal.

Paul67

Thanks all, that's good news.

Joe Sprintbros

After re reading this post, I realized the question by the OP flipped during the course of the thread, so to clarify, a rect intake will seal on oval head with rect gasket, but I'm not 100% sure the opposite is true. I think will depend on if the oval port intake has enough material to cover the rect head port, I don't have nay experience with that.

Paul67

Joe - sorry for the confusion, I should have started a new thread, I really was wondering about the performance experience of the Square intake with Oval heads, I realize it will work, just wondering how well it works.

Paul

Joe Sprintbros

I am sure it is not optimum, but will function, probably not noticeable on street. FWIW, I used the factory rect intake on a very mild, budget 427 in 69 Camaro bracket car, mild hyd cam,780vac, stock conv, ran 7.60's/89. I think the cool factor of the 3x2 would offset diff in hp!

Jebbysan

....Oval Intake on Rec head...Hmmmm....
Take a rec gasket...and hold it up to the Oval intake....the physical
overall casting may be scalloped on the bottom side and along the top.

The runner may be too small on the outside of the runner...thus exposing the rec intake port.

Visual check with gasket will tell you....hold it to the heads as well...

Jebby