[J.C.you]

Anyone ran one with a hyd flat tappet 400 ci? Thinking of using one since have one on shelf. 230 cfm 13 heads, ra iv cam advanced, 9.5 comp

….I know not the best application of parts, just using stuff already have for a budget build.

I have a stock intake but don’t want to choke the heads.

[Cliff R]

For what you are doing the only thing gained from changing to an RPM intake is taking about 27 pounds off the front of the car. You may even loose some power if the taller intake requires a drop base air cleaner moving the air cleaner lid closer to the carburetor.

So no, at your power level the RPM intake really isn't worth the effort......IMHO....

[J.C.you]

Cliff, you are right, be a 70 GTO so have some hood clearance. Have you done any spacer testing on the rpm?

[slowbird]

We ran rpm on 400 with ported 62 heads, runs good

[prostreet64]

My son's car with the 400 has had the RPM for many years. We went through a series of flat tappet hydraulic cams with the last being the XE284. Always used a 1" spacer and 4" air box. Had to go to a cowl hood to get the needed clearance. Heads, #64, ported to 250 on the intake side and c.r. at 9.7 to 1. This combo yielded a best of 11.69 at 115 on 93 octane. As Cliff pointed out your combo may not benefit from the RPM but it is an excellent intake for the 400.

[J.C.you]

Originally Posted by prostreet64

My son's car with the 400 has had the RPM for many years. We went through a series of flat tappet hydraulic cams with the last being the XE284. Always used a 1" spacer and 4" air box. Had to go to a cowl hood to get the needed clearance. Heads, #64, ported to 250 on the intake side and c.r. at 9.7 to 1. This combo yielded a best of 11.69 at 115 on 93 octane. As Cliff pointed out your combo may not benefit from the RPM but it is an excellent intake for the 400.

Nice, the car pick up with the spacer?

[Formulajones]

The only Pontiac I've played with the RPM intake on was 455's. Had one on the dyno and played with spacers. It liked a 1" open the best but wasn't huge gains. If I remember right it picked up 7 or 8 hp. The 4 hole spacer we tried lost power, just didn't like it for what ever reason. I think one possible reason is because the Pontiac version of these RPM intakes don't have the divider cut down like other engine brands do with the same intake.

Either way, it may not apply, not sure how a 400 might react differently. Easy to swap around though and experiment if you have the time.

[PAUL K]

I think the RPM will work good on a 400 with 230 cfm heads. The carburetor choice will have an affect on spacer choice.

[Formulajones]

Paul is correct, I should have mentioned that specific dyno test was with a 950HP carb.

[J.C.you]

Originally Posted by PAUL K

I think the RPM will work good on a 400 with 230 cfm heads. The carburetor choice will have an affect on spacer choice.

Just be period correct qjet. Have a open spacer throw on. Maybe take to track before year out for giggles.

[Steve C.]

Posted for interest only. The application here is certainly not apples-to-apples with the OP's proposed combo.........

Dave Bisschop intake dyno testing....

474ci engine / 290cfm CNC ported KRE D-port heads with 10.2 to 1 compression on 91 octane fuel with a 236/245 duration hyd. roller cam.

Intakes gasket matched to a 1233 Felpro gasket, each intake was mocked up to make sure port alignment was correct and each intake had the water crossover removed.

Stock iron factory intake with Q-jet carb.
515hp @ 52-5300rpm and 575 lb/ft @ 4000 rpm.

Factory cast iron with the CNC machined plenum with Q-jet carb.
527hp @ 5300rpm and 579 lb ft @ 4100rpm.

Edelbrock Performer RPM
541hp @ 5400 rpm and 591 lb ft @ 4000 rpm.

"The purpose of this test was to see how each intake behaved in this particular engine combination.
Other combo's can and will have different results but I felt this info would be interesting to our customers to look at and may be helpful in parts selection"
Dave Bisschop



.

[prostreet64]

Originally Posted by J.C.you

Nice, the car pick up with the spacer?

With our combo the car picked up a tenth with the 1" spacer. We used the Jim Hand design to modify an open spacer where the spacer separates the primaries but is open across the secondaries.

[PAUL K]

Originally Posted by J.C.you

Just be period correct qjet. Have a open spacer throw on. Maybe take to track before year out for giggles.

That may help. If you wanted to spend money you'd probably find some power with a four hole tapered 1/2 spacer.

[J.C.you]

Originally Posted by prostreet64

With our combo the car picked up a tenth with the 1" spacer. We used the Jim Hand design to modify an open spacer where the spacer separates the primaries but is open across the secondaries.

Nice gain!

[Dragncar]

Originally Posted by Formulajones

The only Pontiac I've played with the RPM intake on was 455's. Had one on the dyno and played with spacers. It liked a 1" open the best but wasn't huge gains. If I remember right it picked up 7 or 8 hp. The 4 hole spacer we tried lost power, just didn't like it for what ever reason. I think one possible reason is because the Pontiac version of these RPM intakes don't have the divider cut down like other engine brands do with the same intake.

Either way, it may not apply, not sure how a 400 might react differently. Easy to swap around though and experiment if you have the time.

I took a standard 4 hole spacer and used a jigsaw to make it a big 2 sided slot and then cut a notch between the secondaries like the other brands have.
The engine seemed to like it. I was afraid to actually cut the RPM so I cut a spacer up.

[Formulajones]

Originally Posted by Dragncar

I took a standard 4 hole spacer and used a jigsaw to make it a big 2 sided slot and then cut a notch between the secondaries like the other brands have.
The engine seemed to like it. I was afraid to actually cut the RPM so I cut a spacer up.

Yep, I do that trick when I use Q-jets on factory manifolds, and blend everything. Works really well.

Did you do that with a holley carb? I've been wanting to try that.

[shaker455]

Originally Posted by J.C.you

Anyone ran one with a hyd flat tappet 400 ci? Thinking of using one since have one on shelf. 230 cfm 13 heads, ra iv cam advanced, 9.5 comp

….I know not the best application of parts, just using stuff already have for a budget build.

I have a stock intake but don’t want to choke the heads.

JC,
Maybe consider an early Edlebrock large runner P4B QJ.
I have been running one on my 67' GP 400 with great results.

Rocky Rotella reported better flow then stock intake

A good alterative if you don't want the height of an RPM.
Jeff

[i82much]

is there an intake manifold on the engine right now? if not, the rpm will be easier to carry across the shop to install ...

[J.C.you]

Originally Posted by i82much

is there an intake manifold on the engine right now? if not, the rpm will be easier to carry across the shop to install ...

Hahaa, as matter of fact just dug the rpm out , blasted around on it some. Don’t like to advertise and like the factory look, so ground the e stuff off and be painted 1616.
Found a old 5/8” spacer too. Anyone care to share their mods so I can copy (grin) while I have the grinder out?

[Dragncar]

Originally Posted by Formulajones

Yep, I do that trick when I use Q-jets on factory manifolds, and blend everything. Works really well.

Did you do that with a holley carb? I've been wanting to try that.

Yes, Holley.
This is my spacer. I think I should have tried a smaller slot first but what I ended up with seemed to work well.