How much HP will a RPM Airgap support

[Erland Cox]

What did you do with your intake David?

Erland

[David Vizard]

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.

Dave,
May be able to accommodate you on this test. Call me

DV

[David Vizard]

What did you do with your intake David?

Erland

Port matched only. Had a Braswell 4150 flowing almost 1050 cfm.

DV

[Erland Cox]

OK, thank you! Amazing that the ports in the manifold can feed that much hp.
What do the heads flow with the manifold?
Did you try the same heads with a bigger manifold?

Erland

[GARY C]

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 ...

The reason they don't do that is because you end up with a bunch of half a$$ compromised intakes and your name gets destroyed over time from press about less than optimal results, we have a history of those kind of intakes, none of which are produced any more for a reason.

[Keith Morganstein]

I've built a few SBC engines with air gap intakes, but only had one 355 with 210 AFR race ready heads on a dyno. It was my typicall competition prepped small block build. It only made a bit over 550 HP. What really impressed me wasn't the dyno HP, it' was the absolutely explosive driving performance of the engine.

I would say that is where the air gap "shines", not necessarily in ultimate HP, but in very strong midrange performance.

[bigjoe1]

I agree - The seat of your pants dyno is very strong.




JOE SHERMAN RACING

[F-BIRD'88]

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 ...

The reason they don't do that is because you end up with a bunch of half a$$ compromised intakes and your name gets destroyed over time from press about less than optimal results, we have a history of those kind of intakes, none of which are produced any more for a reason.

This makes no sence and does not hold water.
A good intaje is a good intake.

[lefty o]

a good intake is a good intake, until youve modified it so that its no longer the same intake.

[kimosabi]

I've built a few SBC engines with air gap intakes, but only had one 355 with 210 AFR race ready heads on a dyno. It was my typicall competition prepped small block build. It only made a bit over 550 HP. What really impressed me wasn't the dyno HP, it' was the absolutely explosive driving performance of the engine.

I would say that is where the air gap "shines", not necessarily in ultimate HP, but in very strong midrange performance.

I don't even have the air gap, just a 7104, and my current afr 210 head 400 sbc with a qjet is what you describe. 232/232 108 hyd roller cam and 10.6:1 compression. Angry street engine. Killed my driveshaft in 2 weeks on the street.

[gnicholson]

big joe dv or anyone else. which manifold between the air gap and the plastic afr dual plane would you use for a street 427 sbc. 11 to one 215 dart 250 260 on 106. it has a stock suoer victor on it now. trying to smooth up the engine at 2k without killing the top end

[cjperformance]

Assuming correct timing and fuel at 2k rpm,, have you simply tried some different spacers 1st? They can make as much or more difference to driveability at given rpms than they can to w.o.t. hp numbers.

[F-BIRD'88]

Replace the super vic single plane with a dual plane high rise like the performer rpm intake that has a
full divided plenum. You an then try a hybrid style carb spacer on that.
See how that works. You want that divided 180deg plenum of a Dual Plane manifold.

You will only get so far with that 250-260 106 camshaft. The overlap creates a lot of reversion and exhaust remix at 2000 rpm. Correct timing and fine tuning the idle off idle circuit on the carb will go a long way.
Idle air bleeds, IFR, idle transfer slot feed restriction. A moderate amount of intake plenum heat
makes a huge difference. Heat promotes fuel vaporization at low running speeds.
Liquid fuel will not burn.

[F-BIRD'88]

If you want to try and improve the single plane intake you can try a heated plenum "turtle" with a plenum divider too. A turtle insert with a internal HOT water jacket passage would allow circulating hot water or hot exhaust to heat the plenum and divider.

The divider cuts the exhaust reversion in 1/2 and essentually doubles the carb signal to any 1 cylinder.
If the carb is small you will give up a bit of top end peak power with a divider.
If the carb is big the trade off will be small(er)

Added plenum heat goes a long way to improving fuel vapourization quality at low engine speed.
If the car has a Auto trans you will probably find that locked out timing+ correct rate and amount limit vacuum advance works best.

But for what you are trying to do a Dual plane manifold (with full divided plenum) is going to be best.
(especially with plenum heat) If the carb is big you won't mess the small top end difference.
The low-mid torque gain is huge
A dual plane 180deg manifold can use and wants a bigger carb or 2x4bbl carbs

[gnicholson]

I'm sure the heated intake would help but this thing is mostly driven in warmer weather and a manifold is plenty heat soaked. I realize I could tune this thing a little better but I've worked on it a great deal and it's pretty close to as good as I can make it. I think just as you have already said that a dual-plane would make it better and is an easy option to try. I just don't want to cut the top end Power more than I need to so I was wondering about the flow capacity of that manifold. I thought maybe the AFR dual-plane would move a little more aiir . I will definitely need to put a larger carburetor on it the 750 on it now coupled with a dual-plane will definitely hurt top in power thanks for the replies