Using rectangular port intakes on oval port heads

[69L72RS]

Steve,
I'm getting old so I may not explain this exactly right.

If I remember my fluid dynamics correctly, the mismatched ports create "eddies". These areas are stagnant and don't actually flow with the intake stream. They kind of create an invisible funnel effect at the oval port entrance.

As an example think of this crude comparison.
Which has less restriction?
1) a 24" piece of 3/8" id fuel line or
2) a 24" corrugated flex funnel(with 3/8" outlet)

The funnel will have a higher volumetric flow for the same value of negative pressure (vacuum), even with irregular inside surface (from the flex corrugations).
This is due to a function of laminar flow and length to ID ratios for the two flow paths

I hope this helps. Its 2 am and my brain hurts now.

PS: We used the following trick when we were to poor to afford rect port heads and wanted to run an aluminum holley intake.
We would epoxy about 2 inches of the rect. intake runners and port match them to the oval port heads. This created a smoother transition from the rect to oval runner.
This combination ran better than a full rect port setup a lower rpms, but didn't carry the power past 6500 on 396's.

That's all for tonight folks.
Eric

[Stefano]

I have seen it done many times, over the years. The engine will run without trouble. I don't know all that stuff Eric was taking about, but can tell you that, IMO there is no way the Square to Oval configuration will run as good or better than the Stock Square to Square or Oval to Oval configuration.

[HS PROFESSOR]

Lets get one thing straight...I'm not going to get into an internet Argument with anyone and obviously oval to oval and square to square is the best idea but check this out.....



Had a 70 nova with a 454 with closed chamber pistons.compression ratio ??? I bought a set of new 990 squareport heads to try instead of the closed chamber oval ports. did nothing but change the heads and put on a old sideways sqareport torqer intake. the car went from 12.70's to 12.20's.and gained about 5 mph.when it was time to sell the nova i pulled my new 990's off and all i had at the time were a set of peanut port open chamber truck heads.So i changed the springs and on they went.I never liked the sideways intake so decided to throw it on and hope it ran ok. I wasnt expecting any performance at all from this thing ,all i wanted was to sell it and move on. All i can say is ....TOTAL SURPRISE. As soon as i fired it up,it sounded good.But when i drove it,it felt better.It made a ton more low rpm torque,and just ran unbelievably well.I had to take it to the track and see and believe it or not,it ran 12.50's.Total mismatch of parts and i mean TOTAL.It had a .560 lift lunati solid cam,10" conv.,and 4.10 gears. The mph dropped about 3-4 and it didnt like to go 6500rpm's anymore,but it spun to 5500-6000 no problem.

The moral of the story is....Dont mock it until you try it,and even though on paper it should never work, you never know. I've done it and it worked.will i do it again.....Not unless i have a reason too, but i know it will/does work.


hope that helps....bob

[Keith Tedford]

We took a '74 smogger 454 and added a Cam Dynamics 272 energizer cam, rectangular port intake, 750 Holley, and headers. At 3900 pounds with driver the car ran 102.4 mph with no special tuning what so ever. With traction that equates to about 13.2-13.3, if you had traction. Bottom end torque was excellent. Not bad for a total under the hood investment of about $1K including the engine. The torque felt like our L72. It was a pleasant surprise. Not many cars run as well for so little invested. Others have used this intake on race oriented oval port engines with excellent results. Add to that the hipo Chevy look and the intake is worth it even if it didn't work.