How much HP will a RPM Airgap support

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DaveMcLain
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Re: How much HP will a RPM Airgap support

Post by DaveMcLain » Mon Sep 04, 2017 12:49 pm

Erland Cox wrote:OK, thank you.
I would never had believed that a dual plane could be so close to a single plane manifold in such an high hp application.
We have made almost 700 hp on a big block with the stock aluminium dual plane.
But only on the forst pull.
Power drops up to 50 hp because of heat soking at the second pull and then stays the same.
Despite a valley tray to keep hot oil off the bottom of the manifold

Erland.
As Joe says in his posts you need to run a big carburetor on a dual plane to make it run well because the cylinders only see 1/2 of the carburetor. I have a Dominator adapter that I modified with a divider down the middle that I want to test on a dual plane some time. I think it could be interesting on a large engine at moderate RPM.

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Re: How much HP will a RPM Airgap support

Post by fdicrasto » Mon Sep 04, 2017 12:52 pm

This is a great manifold for street bombs. Did a 416" sb mopar stroker with 71-72 "J" heads, Lunati Voodoo hyd. roller(UD Harold design) with out of the box manifold, holley 750 D.P. electric choke carb w/ 1" spacer. Made 512 hp at 5600, 568 ft lbs tq at 4200 and from 3400 was over 550 ft lbs tq. 10.9 to 1 C.R. in a 1967 Dart convertible that is a blast to drive.

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Re: How much HP will a RPM Airgap support

Post by DaveMcLain » Mon Sep 04, 2017 1:40 pm

fdicrasto wrote:This is a great manifold for street bombs. Did a 416" sb mopar stroker with 71-72 "J" heads, Lunati Voodoo hyd. roller(UD Harold design) with out of the box manifold, holley 750 D.P. electric choke carb w/ 1" spacer. Made 512 hp at 5600, 568 ft lbs tq at 4200 and from 3400 was over 550 ft lbs tq. 10.9 to 1 C.R. in a 1967 Dart convertible that is a blast to drive.
I would have liked to have tried one on a 408 Windsor that I built about a year ago. Mine made similar HP but didn't make quite that much torque but I was using some parts that the customer already had and that included a single plane Victor JR intake.

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Re: How much HP will a RPM Airgap support

Post by rfoll » Mon Sep 04, 2017 2:18 pm

When I put a 1" open spacer on my RPM Air gap, It was good for another tenth. 406 SBC, 9.7:1 cr 242/106 cam, 780 3310 holley.
So much to do, so little time...

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Re: How much HP will a RPM Airgap support

Post by F-BIRD'88 » Mon Sep 04, 2017 2:49 pm

The RPM air gap manifold should have been cast with a removable "carb adapter" top.
This would allow 2bbl, 2x 2BBL, 1x4 bbl, 2x4bbl (AFB's) or 3x2bbl carbs or EFI or Qjet even a domimnator on different adapters all on the same dual plane hi rise intake manifold. Would also allow for port access for hand porting.
Like this ...
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Re: How much HP will a RPM Airgap support

Post by F-BIRD'88 » Mon Sep 04, 2017 3:24 pm

Tripower carb adapter on top And (you knew this was coming, didn't you)... Dual Q-Jets 8)
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Re: How much HP will a RPM Airgap support

Post by DaveMcLain » Mon Sep 04, 2017 4:12 pm

F-BIRD'88 wrote:Tripower carb adapter on top And (you knew this was coming, didn't you)... Dual Q-Jets 8)
Isn't that really pretty much what Edelbrock did with their newer air gap dual quad design? It probably works ok and it would look cool too.

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Re: How much HP will a RPM Airgap support

Post by Prostreetbike » Mon Sep 04, 2017 7:07 pm

Hey mag2555,
I found the flow numbers for the SBC RPM Air Gap on more than one site. But I did notice that some of the guys post the flow for the lowest port and then show their after porting CFM numbers. Good marketing I guess, so you go from 210 cfm to 270 cfm, which makes the port work and money paid seem very reasonable for the gains. Max impact advertising..no troubles.
Everyone I found showed #7 port to be the worst flowing at about 210 +/- a couple of cfm, and #3 port to be the best at about 226 cfm.That was all just out of the box numbers. I ran across and old article were Dr. J ported an RPM Air gap and got an average of about 290 cfm from all ports, just +/- a few cfm from the best to worst port.
So I can now see how this intake has a lot of potential, which is great since I already have it. Any advise on were the gains are on the port work side for this intake. Thanks guys.
And thanks rfoll for your feedback on your results from using a 1" open spacer. I think I have seen Joe say he always uses at least a 1" on this intake and likes even more if at all possible.

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Re: How much HP will a RPM Airgap support

Post by pdq67 » Tue Sep 05, 2017 6:04 am

F-BIRD'88 wrote:The RPM air gap manifold should have been cast with a removable "carb adapter" top.
This would allow 2bbl, 2x 2BBL, 1x4 bbl, 2x4bbl (AFB's) or 3x2bbl carbs or EFI or Qjet even a domimnator on different adapters all on the same dual plane hi rise intake manifold. Would also allow for port access for hand porting.
Like this ...
What is the bottom's part number?

If it is actually sold?

And Big Joe 1,

How does the old Holley 300-36 high-rise dual plane do here??

pdq67

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Re: How much HP will a RPM Airgap support

Post by mag2555 » Tue Sep 05, 2017 8:09 am

Are we talking about the spread Bore model air gap, or the square bore as the latter has a rated power band 1000 rpm higher!

The number 7 runner feeds off of the short Plenum so using a 1" spacer goes a long way towards helping the flow make the turn out of the Carb bottom and into those 4 runners on that shallow Plenum.

If the outside wall of the 7 runner can be reached and ground taller from halfway thru it's bend and if that port on the roof in filled in and blended out that would help get the numbers of that runner up.

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Re: How much HP will a RPM Airgap support

Post by rfoll » Tue Sep 05, 2017 11:11 am

After the gain with the spacer, I decided a single plane would help. I used a Holley 300-25 and found another tenth. I want to say that if I had a smaller engine and lower stall converter, I would not have seen the improvement.
So much to do, so little time...

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Re: How much HP will a RPM Airgap support

Post by mark_follweiler » Tue Sep 05, 2017 6:23 pm

rfoll wrote:After the gain with the spacer, I decided a single plane would help. I used a Holley 300-25 and found another tenth. I want to say that if I had a smaller engine and lower stall converter, I would not have seen the improvement.
the 300-25 and also the 30-110 holleys are very good all around intakes.

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Re: How much HP will a RPM Airgap support

Post by cuisinartvette » Wed Sep 06, 2017 8:29 am

Wish they still made the 300-36 regret loaning mine out never saw it again. Good piece and had that LT1 "look"

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Re: How much HP will a RPM Airgap support

Post by turbo2256b » Wed Sep 06, 2017 11:14 am

Ran a air gap on my 455 330 hp mercury marine engine. Stock short block installed edelbrock roval port heads had to pocket port them to hit their advertised flow numbers. The engine original heads were the peanut port heads. Test included 3 intakes and 3 carbs. Carbs were 750, 830 and 850. Each carb was tried on each intake. The carbs seemed to make no difference as to performance.
First intake was a Performer RPM which was on the boat when purchased. The boat ran much the same as it did stock lots of bow rise some conditions had to stand up to see over the bow. Next was the RPM Air Gap couldnt tell the differance between it and the RPM other than the price.
Next was the Torker II the boat jumped out of the water like a frog no real bow rise. Got up to top speed 75 (rpm limiter) so quick my 10 year old went off on how much quicker it ran. Was like it added 100 HP. My 23.5 ft boat out ran my friends 18 ft ski drag boat with an engine that cost more than my boat.

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Re: How much HP will a RPM Airgap support

Post by David Vizard » Wed Sep 06, 2017 5:16 pm

bigjoe1 wrote:I have made 615 HP with an RPM Air Gap, But I had a much better AFR head ( 310 CFM ) on a 383 engine

JOE SHERMAN RACING

I like Joe's 615 HP. I suspect Joe may have utilized some of his porting skills on the intake here(if you did Joe let us know).

What I can say in support is that I did a flat tappet 383 with Dart Iron Eagles I ported that crank out 576 hp and 536 lbs-ft from a 12/1 cr.

Those Airgap intakes are just great for the street be it Chevy or Ford.
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