I'm working on a deal for an intake for my 427.It's a rectangle port and I've got oval port heads. Can you make it fit or is it not something normally done? Is it possible to hog out the ports to match the intake or is it too much work?
Throw the rectangle port manifold on the shelf ... and buy an oval port... if memory serves me correctly, the only difference is that the oval port intake combined with oval port heads had a higher cfm flow rate in higher rpm ranges when match ported... The rectangle port has a lot of low-mid range torque which is more desirable for street use than thrashing a high cube engine in the higher rpm ranges say 7000-8500 rpm just to benifit from the oval port.. highgear
If I remember right, I think you can bolt the square intake to the oval heads (not that its the correct way) but it can be done. But you cant put a oval on square heads.
It can be done physically. In the '70s, factory rectangle aluminum intakes were occasionally swapped onto oval port heads to replace the stock oval port intake....and under those circumstances, there were some power gains. It's 2007, & there are some outstanding oval port manifold designs. There's really no justifiable reason to use a rectangle port intake....you can pick up a used oval port intake for under $100. If the R.P. intake is an incredible deal, pick it up & sell it for profit. Keep in mind that even a lot of the aftermarket intakes from the '70s & mid '80s aren't that great, compared to current products. So far as matching the ports...it can (sort of) be done...but you can't modify the oval port to work properly with the intake...there's not enough material back of the port face to do it right...and even if you could, you would be defeating the whole point of using an oval port head.
I picked up a tunnel ram for my 454 for the paltry sum of $40.00 It happens to be a square port and my heads are oval port. Research on the net says that it can be beneficial due to the increased turbulence causing the fuel to stay atomized longer.While this is great for a tunnel ram intake a low rise may not benefit.They also say to use the square port gaskets if you go this route.
Definite yes. I had a 396 oval port motor in my 65' Chevelle. Everything was donated for street racing. I ran a rectangular port intake cuz it was free. Jeez, did that motor run hard. My friend had a 435hp 69' Vette and I "smoked" him. He never believed me till I spun a bearing and had to tear the motor down. Flat top pistons and cast crank. Don't know why the motor was such a freak, unless the port mismatch atomized the fuel better.
What Ratmotor says jives with what I've heard through the years, and really, some turbulence can be a benefit on the street. I've heard that a square port intake on the early round port heads work "real good", but hell, why try it? At the swap meets I look at damn near every BBC intake, the ones with decent prices always turn out to be square port, whats that tell you? Hardly ever find a round port.
Air flow is wild to understand. I would not hurt the head and hog out a factory OEM. I would use any miss-matched exhaust on an oval or round port. I am not racing. If I am a street racer, then that is different story. But, for looks or people pointing at an oval head with a round header, or you fibbing saying the ports are done round... All the pipe is good for is one little pulse in reverse is all that is needed. It will do the pulse on it's own no matter what pipe length, width, metal figured in a D pipe header. The fuel suck is still the dominate tune to the engine, and not a whole lot of R&D to the amateur builder. HP tuning gain is a $$ game changing pipes on the dyno for that 1 to 3 hp gain is to keep the heads on and throw the pipes on that cost the least to buy, (D or oval shaped, IMO).
Thanks guys! It's an old low rise 2x4 offy for the big block...cool factor high ......efficiency factor not so much....... we'll see what happens
see if you can round up some iron rect port heads, and do it right....you'd be surprised how nice a rect port motor runs on the street
I run a 70's Edelbrock "tarantula" intake on the big block in my vintage stock car racer. The heads are the common oval port from a truck, but the intake is for the high performance rectangular port heads. It runs fine...and looks period correct. Is the reversion causing a loss of potential power, yes probably is, but this engine is pretty mild compared to an all-out race engine. You should be fine if you're running the engine for street use.
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