Big block intake comparison

[ezstriper]

Has any body tried a comparison between big block rect. port intakes, I have a factory merc high rise from a 420hp (I think thats where they used it from) it's drilled for both holley and Q-jet and brass lined water passages. I run fresh water so that is not a real big deal to me. any way I've run the performer RPM airgaps and worked well, just wondering if sombody tried them. Thanks Rob

 

[vinny p.]

While rectangular intakes work, I am not a huge fan of them for marine applications. Their intended rpm range is too high. I dont know why Merc ever put them on their factory engines. Personally, I like to run an oval port intake on a rectangular head. The trick is to match the last 1 1/2" of the intake manifold runner, to the size of the intake runner of the head. Its ALOT of grinding, but it keeps the engines torque and hp curve a bit lower.

 

[PayCheck]

Hey Vinny P.,
is this the intake you are ref:
Intake Manifold - GM 454 MAG and 502cid, Bronze Crossover (#6269318)

​

ALUMINUM RECTANGULAR PORT - Holley 4V​

6269318
1972
454

​

Genuine GM Intake Manifold with bronze crossover, required for 454/502 Magnum engines or 454 base engine upgrades.

 

[vinny p.]

I am pretty sure that Merc used a few different intakes. That is one of them. The intake I used on my set up is a Dart oval port with a Dominator base.

 

[RPM]

The Mercruiser 454/502 production engines used a dual plane Winters intake and the HP 450, 465 and 500 used a Dart single plane.

 

[PayCheck]

Merc BBC Intakes...

I couldn't take it anymore, so I went out to the unheated garage and took this pic of the original intakes Merc supplied on the 1994-1995 Gen V Mags. Yes, that's a snow shovel on the left.

As you can see, the intake manifold has rectangle ports to match up with the rect heads 7088 and 6188 - the pics and text by Dennis Moore, page 15. Interesting the difference in port dimensions when matched with oval or peanut heads, and I see what Vinnie means - ALOT of grinding.

I am waitng for a couple of Wieand intakes I bought on OSO, but Dennis swares the originals GM units are worth their weight in gold. I also have the orignal QJets, which are as corroded as the intakes but salvageable if I can source some Nitric Acid..but that's another story.

I'm taking in a lot of information about the induction system of the BBC as I prep for the repower of my '89 Maxxum, and now i have two visions - one with the original intakes, clean/port the original oval heads, and clean up the QJets. This will give me an economical runner with reasonable torque at the bottom end with the stock cam.

The other is with the dominators, wieand, and the 7088 heads I have on the way to see what the WOT looks like with 286 HP cams I have on that pile of parts.....

My son has an Edlebrock rpm on his SBC, but I'd lean more to an open plenum for an allout offshore race.