Yesterday I had the carb off of my 355 SBC. It reminded me of a question I have had for a long time. The manifold is an Edelbrock Performer RPM dual plane intake manifold. It, of course, has the center divider. The gasket I have been using is an open center gasket. This leaves the center divider un-gasketed. A hole approximately .030" x 3.5". So, there is a small amount of leakage between the 2 planes. Now, I know that some guys notch that divider a 1/4" or so. I'm not sure what effect that has? If the gap I have is sealed up, what effect will it have? I'm pretty sure sealing up that gap will have a very small, if any, effect, but I am just curious. The Edelbrock RPM manifold kit comes with an open gasket. I guess they factor the leak into the design, or maybe just ignore it. I don't think either Holley or Edelbrock makes a gasket with the center divider as far as what I have found. I can find 4-hole gaskets, but I don't like the idea of the gasket just hanging there in space. Anybody got a part # for a divided gasket? I'd like to try one out. The motor runs great as is, but I am curious. OH! The carb is a square bore 600 QFT.
Yeah, that's my thought, too! I just got to thinking that if I had a vacuum leak of that size, it would definitely be a problem.
I don't remember such a gasket from Holley, but do not have samples of every single Holley gasket (probably 99 percent, but not all). Carter did make one for Chrysler. Since it has been obsolete for decades, I cut them by hand when necessary for a rebuilding kit. And I would agree with Jim, I doubt you would see any difference. Jon.
Ive always thought that many " modifiers" , especially of the aftermarket or even home shop variety , exaggerated the effectiveness of their " results" !
It has been so long since I cut a gasket, I didn't even think about that! I think I have some gasket material somewhere. I know it will probably make no difference. What are these guys trying to achieve by notching the divider?
I’d always assumed to get more upper RPM use but still have good low/off idle response. But I’m just guessing.
Yeah, that makes sense. Trying to make it work more like a single plane. I think it would be easier to just put on a single plane manifold.
Originally the notched divider was clearance for the 3 barrel Holley. Today when I install any carb with 4 holes on a dual plane I use a 4 hole gasket cut to match the manifold. An exacto knife and straight edge makes it easy.
But I think OP is speaking o a dual plane intake. I do agree fitting a gasket is the proper thing to do.
And a pair of curved fingernail scissors borrowed from your significant other make cutting curves easier! Jon
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