351w intakes

there is no change in the location of the carb when using the performer rpm. who ever told youu that is wrong.

Is your source a checvy guy by any chance?

One of the basics of intake manifold design is to make the runners as equal in length as possible. This being the case, I'd be surprised if the manifolds from different manufacturers varied by more than a few thousandths of an inch.

Now the height of the 351W vs. the 351C might have been a bit different, which would account for a different air cleaner base.

If you're looking for a factory equivalent to the RPM intakes, Ford made them in the late 60's and early 70's. The casting numbers are C9OX, these are aluminum high rise dual plane's. And there were at least two versions with the same prefix but different suffix for the 351W.

2+2GT said:

One of the basics of intake manifold design is to make the runners as equal in length as possible. This being the case, I'd be surprised if the manifolds from different manufacturers varied by more than a few thousandths of an inch.

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This may be the design goal of the aftermarket, by not OEM Ford. The OEM Ford 4 barrel intake has the carb about a half inch farther forward than most if not all aftermarket intakes. In addition, the Windsor shaker moves the top even more forward. If you try to bolt up the factory 351W intake to shaker bracket you will see that it doesn't line up. I have tried it with both the Performer and the Torker II. With the Toker II and a factory Windsor shaker base, the hood opening barely clears the Shaker at the back, and in fact it rubs slightly as you open/shut the hood.

The Cleveland shaker uses a totally different base than the Windsor. All of the other Mustang shakers use the 428 base with adapters tack welded to position the shaker as required (both fwd and up on the Windsor and Boss 302, and presumabley just up on the 390; I've never seen a factory 390 shaker).