seef158

I though I have heard you can bolt a rectangle port intake onto the oval port heads on a 330hp 7.4liter big block, is this true??
I can get a real good deal on a few intakes here locally, one is an rpm air gap by edelbrock, the other is a dart high rise off of a blue mercury racing engine. I know these intakes won't offer much performance gain with these heads but i have plans for a long block 502 or 540 in the future and these intakes would do nicely. I'll probably buy one or the other just to throw on the shelf but if i can put it on the 330 for a year or two i probably will.
would the stock qjet work on this intake also?

thanks.

BY U BOY

yes the stock Q jet will work on the RPM air gap,not sure on the dart. You may see a few hundred RPM's from the change and will also be getting rid of some weight(not much though).
Good luck.

BUIZILLA

your going to have some pretty heavy port alignment issues

Vinny P

I have never heard of that. Some , including myself have chosen to build engines the opposite way. Using an oval port intake on rectangular heads. Then port matching the intake to the heads. If you were to go your way, the flow would crash into the heads, unless you port matched the heads.

Scarab28

Yup - what Vinny said!

Chris Sunkin

It would probably have the same effect as trying to spray a fire hose thru a small hole in the wall. I can't imagine what will happen to the column of airflow when it hits that ledge. The engine may not run at all in your upper RPM ranges due to the flow disruption.

If you try it, be sure to let us know. I've got $5 that says it's a waste of several hours and two good intake gasket sets.

Dave_N

Mercruiser did actuallly use the square port MPI intake and plenum with small oval port heads on the 1995/96 Gen V (pre-L29) 310HP 7.4 EFI/MP Bluewater Inboard and Bravo Models.

tunertech

First of all you can not compare water flow to air flow as water does not compress.

The placing of rectangle intake on an oval port head has been practiced for years. As the air enters the head it has to speed up in order to match the upstream volume enhancing mixture and the speed in which the charge enters the combustion chamber.

The optimum practice is to epoxy the floor of the intake where the mismatch occurs at the head.

The combination adds mid-range gain in torque numbers but does not do much for high RPM performance.

www.mefituning.com

jaxx 30

I have a friend with a runner bottom v-drive w/468 oval port heads, big rect. port tunnel ram, and twin 600 cfm holly. The boat jups out of the water when it comes out of the hole. The mismatch will work but is not effiecient. You could epoxy the ports to match but you should have an experienced person do it. This means more cash out of pocket. I would just hold out for an oval port intake. You can put too big of an intake on an engine. Bigger is not always better. What you want is port velocity. Make the ports to big and you lose it. It seems in boats you need power down low (5500rpm tops). With a 7.4 stay on the small side for ports. Just my .02.

bobl

Mercury actually installed the 454 Mag rectangle intake(carbureted) on peanut port engines in the mid 90's. They only did this when coupled to a Bravo 3 drive. A Bravo 1 got the cast iron peanut intake. Strange but true!