Plenum or Non Plenum Intake

[pcguy]

Here's a pic of an intake manifold that I'm contemplating modifying:



Considering cutting out about 1/2" of the bridge between the two black marks - which raises some questions:

1. Will this increase the potential for higher RPM?
2. Is 1/2" a good number?
3. What would you stuff into the manifold to keep debris from falling into the guts?
4. Anyone have any suggestions as to how to make the cut? Is there a blade for a dremel that might work? Or what would you use?
5. Is this a good idea or should I just get a RPM manifold?

[spencerforhire]

This intake looks like your typical dual plane street intake, designed for lots of low and mid range power. I don't think cutting it will do a whole lot for high rpm power, but will no doubt take away mid range. These intakes have pretty small runners compared to "air-gap"style ones. Why not add a spacer instead? If this is being done to try to try and make some more power in the "mystery" cammed 350 in another of your threads, I really think you're taking the wrong approach.

[pcguy]

The issue is with hood clearance there's about 1/8". As for making more power, I recognize this is not a RPM manifold which could impair top end performance, it occurred to me that since I have the carb off (I'm still working on it) it was worth asking about? I see your opinion is not to mess with it....

So if I don't mess with and I get this kind of working like it should, would you recommend changing the mainifold?

[Wizeguyrc]

That looks like one of those Power Plus china intakes...maybe?
At any rate, I would just about bet if you switched that intake to a real RPM or regular Performer, you wouldn't see any performance increase unless you took it to the track. Then it may only be a few thousands or maybe at best a tenth or two.
If you are just going to drive the thing on the street, spend your money elsewhere. And listen to the good advice on not cutting the intake.

[72 SS PNL]

as with spacers , you gotta do testing to see how much the motor likes , and trimming the intake , is troublesome compared to spacers

it is a old racers trick to lower the divider , ive seen some big blocks dropped all the way down , or as small as 1/4"

[pcguy]

The goal with this setup is 11.5 seconds and while it's streetable and registered, no need to take it on the street. Not sure what I have to do to make 11.5, but I hope to find out. Got some parts ordered to get the carb set up better (correctly?), but based on the above I'll hold on cutting the bridge. Looks like the power valve on the Holley was not only the wrong one, but it also was blown. Hopefully a the new one won't change the idle vacuum much, if so, it could throw off the calculations made for selecting the new one.

[spencerforhire]

The blown power valve was no doubt a big part of your problems. Make sure whatever you put back in there is sized properly.