Tom Wilson
May 5, 2003

When you're the big dog on the block, there's one thing you just can't let happen--allow another dog to take even a small piece of your territory. If you do, all the other dogs will get the same idea and the fur will really fly. In the world of intake manifolds, the big dog is Edelbrock.

By automotive aftermarket standards, Edelbrock is something of a cross between a Great Dane and a pit bull, as it's a large company with a broad product range, so it must keep sharp thanks to a pack of competitors nibbling away at its heels.

With the success of competitive intake manifolds on fuel-injected small-block Fords the last couple of years, the company has been taking bites large enough for Edelbrock to notice--and not only notice, but sit up and bite back.

This application of the canines has been cast in aluminum and given the name of Performer RPM II. Offered as PN 7123, the new RPM II is a direct development of the Performer RPM, even though the upper intake has a decidedly new look to it.

As he was with many other intakes, Edelbrock engineer Brent McCarthy was responsible for developing the Performer RPM II. His primary goal was to improve high-rpm airflow without losing power at lower rpm. This would give the RPM II the sort of track muscle it needed to outrun the other breeds that have been doing fairly well at the strip.

Because the Performer RPM's lower-rpm air delivery has always been good, there was no need to adjust it. The goal there was simply to maintain what was already on hand while pumping up the top end.

Brent knew that, by itself, simply increasing runner volume or decreasing runner length would help the top end but hurt the bottom end, so that tactic was out. But the crossover--the runner connecting the throttle body to the runners--was the obvious area in which an improvement could be made. The Performer RPM uses a generally tube-shaped crossover, which is constrictive at high rpm and doesn't necessarily provide the absolute last word in flow distribution to the eight runners. Taking this logic to its inevitable conclusion, Brent gave the RPM II an opening--"reverse taper" in engineering-speak--crossover. Its triangle shape has been seen before on moderate runner-length 5.0 intakes, and it certainly seems to work well.

To support the increase in top-end power, however, some runner enlargement was required. This was easily accomplished in the upper intake, as the casting cores were being reworked to accommodate the new crossover anyway. Then, to ensure a sharp port match between the upper and lower intakes, CNC clean-up of the runner throats was specified.

In real terms, the upper intake runners went from the nominal 1.90-inch RPM dimension to 2.58 inches in the RPM II. That's about 30 percent larger. In area, at the throttle-body opening there is approximately 8 square inches of area in both the Performer RPM and RPM II intakes, but the RPM II opens to 12 square inches at the plenum (between the end of the crossover and where the runners begin).

It would have been nice for everyone if the existing Performer RPM lower intake could have been used precisely as-is, but minor changes were required. If nothing else, the runner openings had to be CNC'd to match the larger RPM II upper runner openings. The lower runners themselves, however, are unchanged, meaning the runners are essentially straight, untapered passages. Furthermore, to accommodate the desired runner length and packaging concerns, the lower intake's upper flange--where the upper meets the lower--has been machined down approximately 3/8 inch. Thus, Edelbrock can make the Performer RPM II lower by beginning with a Performer RPM unit and giving it a couple extra machining steps. This also means Edelbrock has decided to offer the Performer RPM II only as a complete upper and lower package. Therefore, the company will not sell the upper by itself; you have to buy the entire manifold.

At press time, we were able to photograph the first preproduction Performer RPM II, but the absolutely final massaging of the production tooling had not been done, and obviously production RPM II units were unavailable. However, no one at Edelbrock expects anything meaningful to change between this final prototype and production, so the dyno and flow figures we're citing will hold true for the units you can purchase.

Pricing will also remain close to current Performer RPM practice. And just what improvement was Edelbrock able to breed into its new top-dog RPM manifold? Well, airflow through the crossover picked up approximately 20 percent compared to the Performer RPM, and that flow increase seems to have made its way through the runners.

On Edelbrock's dyno, the RPM II did its job perfectly. It runs neck-and-neck with the Performer RPM all the way up to 4,750 rpm, then continues building a noticeable knob of top-end power at least up to 6,000 rpm as the RPM signs off. As Brent put it, "This is going to be a great manifold for anyone who wants loads of bottom-end torque and great top-end horsepower. It will make a street/strip car both driveable and respected at the track." And, in this case, the bite is right up there with the bark.

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Horse Sense: A downside to being big is it can be difficult to react swiftly. Edelbrock was a bit tardy to market with its first 5.0 intake manifolds, for example. But the upside is that a large company such as Edelbrock has the resources to optimize and improve its products where others can't. Kudos to Edelbrock for revving up the RPM with the RPM II.
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With its gray paint, the Performer RPM II upper is a fine sight on any engine. Following traditional Edelbrock practice, the lower intake is natural aluminum. For now, the Performer RPM II will supplement, not replace, the Performer RPM manifold. However, market pressure will likely make the straight RPM intake obsolete, as the RPM II has similar torque and more horsepower.
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Edelbrock packaged all the upper bolt holes so they are easily accessible from the top of the intake. This led to a couple of cast pedestals passing through the upper intake, which doesn't seem to hurt anything.
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Beginning with a standard Performer RPM lower intake, Edelbrock only had to port-match the runner openings to properly mate with the larger upper intake runners, and lower the upper mating flange 3/8 inch for packaging reasons.
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Edelbrock has long had a winning lower intake manifold with tall, straight runners. This view through the RPM II version shows that CNC port-matching hasn't harmed any of that.
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Here's a look at Edelbrock's in-house engine-dyno comparison of the RPM II versus its RPM little brother. As you can see, the RPM II gives up just a bit on the bottom end to the RPM, but the top-end gains are impressive. We bet this baby will really like a blower, and we can't wait to get our hands on production pieces to find out.
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(left, above, right) Get anywhere near the RPM II upper intake and there's no missing thetriangular shape of the new crossover air passage. It's a shape that'scome to dominate short-runner 5.0 intake-manifold design.
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(left, above, right) Inspecting the Performer RPM II upper intake from all angles shows it isfully equipped to accept all standard 5.0 hook-ups--even EGR. Unlike thePerformer RPM, the RPM II does not have a bolt-on plenum cover, exceptfor a small one on the bottom.
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