RPM or stock iron intake
 

for a street car, cleaned up #13 heads, RAIII iron headers, roller cam, havent picked one yet but nothing too wild, 4 speed, 3.55 gears, q-jet.
which is better?

pretty close to each other. if you want some weight savings, the rpm. otherwise a pre-smog 4bbl stock intake with a port match job will work just as well.

What is this going on? The RPM work very well on 389+ motors and they were worth about 1.5-2 mph over a 67-72 iron intake. But keep in mind they are about 1.5" taller than stock if you have a limited hood clearance.

The Edelbrock Performer (no "RPM") and the stock iron QJet are about equal. The Performer RPM is a different manifold and is superior to the stock iron QJet for drag racing and as noted above is taller than stock.

The aluminum Pontiac RA4 intake is also a consideration and also has a taller port to be blended on stock heads and also have the proper height so you can use them on cars with shaker hoods you can also leave out the iron crossover to keep your intake cooler than if you just blocked off the the heat risers. like so...........
http://www.pismoderelicts.com/photog...s/p1020753.jpg

D.

I'd go w/ the iron intake, even if it's an unaltered stock one.

It seems like a RPM would be best, mostly on the largest cube engines (455+) or higher RPM engines. Cliff and Jim Hand used modified stock iron intakes, making a boat load of power.

I believe Jim is currently using a RPM, he has slightly enlarged the intake ports on his 6X heads, and turning a fuzz more RPM, both possibly allowing the RPM to function as the more desireable intake, for his combination. Maybe Jim will read this, and comment...

A correctly modified intake is a VERY good intake. I like the idea of a "stock" intake w/ a "stock" Q-Jet on my engine, then take one of the "know it alls" for a ride and show them how well a stock Pontiac engine performs!!!

The aluminum RAIV intake is a desireable piece, but used ones are priced high??? and hard to find, and the reproductions have issues???

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Well yes they are expensive if original OE, but they are now being reproduced.

D.

Several years ago we did a back to back dyno test between an HO intake, my iron intake, and an RPM intake. All were port matched exactly to a stock Felpro blue intake gasket.

No spacers of any kind were used, same carb, and same gasket. The HO intake was the reproduction unit, not an original. I opened up the HO intake and the iron intake to the same size/shape as the RPM under the carb. The runners were not ported, just the work under the carb (pics attached).

The engine we used was a 428 (434cid), 74cc KRE aluminum heads (prepared here), 10.6 to 1 compression, 236/242/110HR camshaft with 1.6 ratio Crower roller rockers.

The HO intake made 487HP, RPM made 491HP, iron intake made 497HP. An interesting tid-bit about the dyno numbers, even though the RPM made less power, it made it at 200 rpm's higher (TQ and HP) than the iron intake.......Cliff

Cliff,

I notice that the iron intake, in the picture, has The divider cut down. Did any, or all, manifolds have it cut down during the test?

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Just curious Cliff, you say you used a stock Fel Pro gasket, I take not the tall Fel-Pro RA4 gasket??
I can understand the Hp , I would like to know at what RPM? Correct me if I'm wrong you didn't change the iron manifolds entire runner to match the RA4's? With the exception of the RPM manifold did you use a carb. spacer to keep the throttle blades out of the turbulence of the intake pulses?

Don

No porting to the stock iron or HO intake in the runners, just removed a few "bumps" casting flash, etc.

Stock gasket, not the RAIV.

Peak power at 5800rpm's.

No spacers used, other than a 1/4" thick open gasket.

The dividers are NOT cut down, just added a small "notch" between the secondaries.

The RPM intake is not doubt a good piece. Where it becomes any better than a stock intake is a question we don't exactly know the answer to. At least on a 440cid engine making right at 500hp, it didn't show any more power anyplace. Of course, before someone mentions it, we cheated and opened up the stock intakes to the same size/shape as the rpm under the carb.

I also tested the Performer intake, once on the dyno and once on my old engine making 514hp. It was down close to 15hp on a 455 on the dyno and my engine HATED it. It didn't run well enough to continue testing with it after some brief street driving before heading to the track.......Cliff

Cliff,
Thanks again for the real world facts!!!1

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Thanks Cliff, now your numbers make sense, and I'm surprised you even made that good of a number on the RA4 intake.

Don

That looks like more than a "notch" to me. A notch is cutting down the divider. But, call it what you want. Were they all "notched" in this fashion? "Notching" should improve peak HP. I was just trying to see if some had it and some didn't. Thanks.

Completely different deal to add a small notch between the secondaries, vs removing part of, or all of the divider

It's actually a common practice. We've seen plenty of them heavily cut down and even completely removed. This is a BAD move, from what we've seen. I've had to make dividers for quite a few intakes where it was removed. Doing this can really hurt mid-range power, even if it produces a few more peak HP. It can also induce a stumble, hesitation, or bog, which is difficult, if not impossible to tune out.....Cliff

???

I could not use the stock 1968 4-barrel manifold i had because it sat too low between the heads - appears they were machined to fit some machined heads.

I picked up a used RPM. 35 pounds lighter. I like that alot.

From post #11:

"No porting to the stock iron or HO intake in the runners, just removed a few "bumps" casting flash, etc.

Stock gasket, not the RAIV.

Peak power at 5800rpm's.

No spacers used, other than a 1/4" thick open gasket.

The dividers are NOT cut down, just added a small "notch" between the secondaries."

One last time....ALL intakes were tested in the same manner, same modifications. No dividers were removed, or cut down, just a small notch added between the secondaries.

This really isn't required if you use a 1/4" thick open gasket.

The open gasket allows both sides to see each other in actual use.

We've tested intakes where the entire divider was cut down front to back, and even completely removed. This move can really KILL some mid-range power, and induce a stumble/hesitation/bog going quickly to full throttle.

I've had to notch quite a few intakes at both ends and make inserts for them to put the divider back in place over the years, sent here from folks who got carried away when putting a small "notch" between the secondaries I'm assuming.

If you want it done right, send your stock intake to Dave at SD Performance. He has a CNC scan of our finished product, and will do the work for. On an iron intake, it' takes hours to grind the drivers side down to the size/shape of the intake in the pic above. Those things are some TOUGH material!.

I've done spacer testing as well, but that's another topic. Best advice I can provide in that area....not worth the time or trouble if raising the carb up another 1" or more requires any "cobbling" to fuel lines, throttle linkage, etc, to make one fit....at least for most of the "street" engines folks are doing this to......Cliff

Cliff did the RPM peak at 6000 compared to 5800 for the other 2 manifolds?
Cheers Steve

Sorry. I guess I'm a little dense. It wasn't clear to me, if all the intakes got the "notch", etc.