I've had people speculate on what the end result will be but am curious if anyone has tried this. Rectangular Port Intake matching up to Oval port heads. Now that you've stopped laughing I'll continue. I've been told that the manifold will overlap at the top and the heads will overlap at the bottom thus restricting the flow of air/gas to the heads. The only reason I doubt this is because I see items out there on the market for the C4 mass air flow that are said to add 5hp simply by angling the air. I know know one will notice an additional 5hp, even though the product states "add up to 5hp" meaning under ideal conditions you can see the added hp. Since everything is sealed wouldn't the air be a windtunnl and work itself out? I'm looking for a logical explination of why this won't work and what the reduction in HP would be if it were attempted. If the center of the intake was removed (reducing low end torq) in the above application what would that impact be.

 

"I see items out there on the market for the C4 mass air flow that are said to add 5hp simply by angling the air."

Marketing Hype-

Turbulent airflow will hinder the efficiency greatly. The idea is to have the least amount of non-laminar surfaces for the air to flow across. In this case an extra surface area protruding into the air stream will cause turbulence and hinder the flow.

Find a set that match, or machine them to match. If a budget is the issue, they will work, just not ideal.

Mark

 

Many years ago this was a common thing. But this was before decent oval port intakes became available. To make it work, the heads need to be opened up to match the intake as far into the port as possible. It can be done...in fact I've done it several times successfully,but it does take work. It usually worked well on 396-427's with oval ports and serious cams etc.

Just bolting it on there will physically function, but the performance will not be up to potential by a long shot. I would expect much more than a 5 hp difference. You are talking about a huge mismatch, not just a little.

If your current intake is really bad, then it will probably run better, but it's not worth it unless done right. Unless you just want to do it for looks...but then I have to question why?

The removal of the plenum divider is going to do just what you expect. It will move TQ curve higher. Great if you are running engine in high/narrow rpm band. Terrible if you actually have to start from a standing start and shift gears without lots of gearing.

Just look at the work folks do to port heads. You do everytrhing you can to make a smooth transition with no restriction. The HP increases can easily be 40-100 hp with good head work. If you think about it, you can imagine what happens when you stick a 1/8- 3/8" wall up at the port entry. Not 40 hp probably, but I still think you should look for th proper intake.


JIM

 

Mismatch of the ports was is not a long term option, I was just curious to the real outcome of this set up. Based on the response the smaller SQ ports give you the smaller hp so I'm sure the mismatch would be even less. I'm looking at changing out the heads and might just go back to my edelbrock performer and stick the GM intake on ebay.

 

is it a 069 intake? if so, drop me a line, maybe we can make a deal (save eBay costs :-)

ronin45230@aol.com

 

Regarding the L-72 plenum divider mods.....

I went from:
- a stock L-72 intake with a L-72 780 Vac Sec carb, to
- a notched plenum L-72 intake (1 x 2.5" notch), and an 850 DP
- to a L-88 open plenum intake with corresponding stagger jetted/flow tabbed 855 CFM ZL-1 DP (choke removed, flowed 870).

But my plan is to make max power 4500-7200 with a "fairly stock L-72 appearing" 468 inch BB and reduce low RPM power to SB levels to assist in launching with the skinny tires. Gearing = 2.56 WR M-22 with 4.11's (10.5 overall) so with a 2000 RPM launch 4500 RPMs in 1st comes up very quick, maybe to quick.

Let you know how it works when the weather clears up here in MI.