Intake manifold question
 

Can you safely use a GM rectangle port intake with GM oval port cyl heads ???

I have a chance to grab a Whipple supercharger kit but I've got oval port heads and it comes with a rect port intake. If possible I do not want to have to get new heads.

Any ideas ???

Thanks

Funny you should ask.... but when I disassembled The "Too Old's" Sonic I bought, I found one Gen V-454 with peanut port heads and a rectangular port intake on it. Fred (Too Old) was told by Magicfloats mechanic it ran fine, but certainly it shouldn't. Disrupted fuel/airflow to the cylinders would kill any normal performance out of it. Not to mention fuel puddles laying at the intake flange when the engine is turned off. In otherwords, yes it would run- but that is all it would do......
forget it!!:eek:

:D :eek: Oh my Gosh!! I just remembered, today I saw on OSO a set/pair of complete heads with mild porting and dyno time only on them for $400.00....
That is supper cheap. Buy those heads & The Whipple kit and you will be good to go!!:D
The heads were in the Platinum Member Parts for sale listings......

What if you went the other way,large port manifold to smaller port head.

Better, but still not good.

Hey, why not get the blower and a set of used heads. The stock heads are almost free.

The heads currently on the motor are good and have all the good stuff in them already.

Since Blown Formula said the motor ran. I bet this would work for now.... remember this is going to be a pressurized application so flow is not as important as on a N/A motor.

Flow is still important as in disruption of flow. Rectangular port heads can be had cheap. Don't try to take the easy way out. It doesn't work.
I just sold a pair of GM 990 heads setup for a blown application for $500. If your present heads have all the good stuff, they are worth something to somebody.
You are stepping into a whole different world. Do it right!

Yea, rect port heads with oval prot intakes work pretty darn good. But not the other way around.

Bummer--No need to worry about this anymore. I lost out on the bidding on the Whipplecharger setup.

Back to the drawing board !!!:D :D :D

If the chance presents itself do it. I've done it before, and I'd do it again.

large intake to smaller head opening is very disruptive to airflow but merc used large oval port manifolds with the peanut port heads on the 330's. This was just as bad a mismatch the mainfold being 1.5" x 1.9" and the peanutport head being 1.5" x 1.4"

as for going the other way small intake to large head opening its not as disruptive to air flow and again on mag mpi motor the merc intake manifold is 1.4" x 1.9" and the large rec port heads 1.5" x 2.2"

I always wondered about the merc mag mpi manifold, it doesn't match anything, it is much smaller than the rec port , actually being the same height/width as a large oval port but it is almost square in the corners and so is a mismatch for large oval port heads to

Merc's 7.4litre matched to a Bravo III was called a performance tuned engine and was rated at 300 hp but talk to anyone at merc and they really made about 310 hp. This was due to the use of a rectangular port aluminum intake (with brass water jacket inserts) and different jetting in the weber carb compared to the std 7.4. Both engines still used the small peanut port heads. I think they did this from 1994 to 1996.

oval port mfd. on rect.heads
 

how canyou put an oval port manifold on rect. port heads? the manifold does not cover the rect. port opening.. just would like to know....Ken

think gaskets

The oval gasket is to small, and the retc. gasket leaves an opening at the top. I don't see how it can be done with out welding the oval port manifold. Ken

Lab Engine in Lindenhurst N.Y. does this all the time.
there has to be a gasket that works. When I get a chance I'll check my stock. You might have to remind me as I'm going to work tonight. I love my Holley Cast Iron hi-rise squarebore manifold. Although having to open up the throttle bores with a die grinder. It's an excellent runner. I believe Lee at LAB uses a Merlin aluminum manifold with bronze passages. I think that if the holley squarebore large oval cast hi-rise manifold was not discontinued over 35 years ago it would have been found on factory Merc. motors. Another lesson learned by reading Dennis Moore's fine publications! Also depending on rpm range , using the oval manifold on Square port heads can increase usuable torque. It has been dyno proven. BBB