RPM Air Gap Manifold - Losing sleep over fitment.

[Scotti]

I am the guy that found a full size bath towel under the intake (see my other post) while swapping manifolds a few months back. Upon closer inspection, the cam was flat, the crank and main bearings had one foot in the grave etc. Well fast forward to today, the motor has been at the machine shop getting rebuilt with a lot of nice go faster shiny goodies and draining the wallet. Here are the specs…

1965 coupe
1969 302 Block
9.5 Compression
Balanced
Comp 238 cam. 262/270 duration, 110 degree Lobe and 500 lift.
Comp Cam Roller Rockers
Edelbrock Aluminum E-street Heads (ported with higher end valve train installed)
My old Performer Manifold
Demon 625 Street Avenger Carb
20% Under driven Aluminum Pulleys
Stainless Headers Duel Exhaust
C4 with 2200 Stall
Posi Rear with 325 gears

Additional info:
Car has C4 Auto Transmission, Front Disk Brakes and Air Conditioning (aka needs vacuum). Also I am running the 1966 Motor mounts (have read that they cause the engine to sit slightly higher than the early 1965 mounts)
I know this has been discussed everywhere with mixed answers. My question is: I want to run a RPM Air Gap Manifold (Endurashine of course) – Under the stock hood – with the small 2 inch tall billet specialties oval air cleaner.
Will this set up fit under the stock hood. Looking for proof or thoughts about fitment – I am kinda losing sleep over thisJ thanks in advance.
Also any thoughts on my set up, suggestions for improvment?
Scott

Added 2/22/13: I still don't see how will fit under the stock hood....

Also, I am re thinking the Comp Cam from the XE262H (262/270 duration, 110 degree Lobe and 500 lift.) to go with the next size up XE268H (268/280 duration, 110 lobe with 512 Lift). Do you all think this would be a better cam for my set up or a bad idea? Thank you for all the advice.

[wheelsup351]

the air gap will be about 3/4 taller at the carb than the performer.

i dont see how you'd benefit from the air gap with your current setup.

your combo looks good as is imho.

[6t9mach1]

Originally Posted by wheelsup351

the air gap will be about 3/4 taller at the carb than the performer.

i dont see how you'd benefit from the air gap with your current setup.

your combo looks good as is imho.

Seriously? He has a larger then stock cam and aftermarket heads...

A high rise dual plane intake would be a major upgrade over your current Performer intake. You wont have a problem getting an air cleaner that will work with that setup. You may need to get a drop base air cleaner bottom but you can get it to fit.

[Scotti]

Plus the Air Gap just flat looks awesome cool...

[jdub]

Originally Posted by wheelsup351

i dont see how you'd benefit from the air gap with your current setup.

your combo looks good as is imho.

I second the seriously? The Performer is a DOG of a manifold. No reason ever to run it on an SBF unless you got it for $50. Shelby taught us long ago that even mild, stockish SBFs want a high-rise manifold.

I believe Kenash on here ran a Performer RPM, 1" Spacer and 3" K&N filter under the stock hood. According the Edelbrock, the RPM and RPM AirGap for the 289/302 are the same height (although this is not the case for the 351W version).

[wheelsup351]

i had an airgap on an old 308 that ran basement 12's. i also had the rpm right before that (both motors had much bigger cams than the 238). the difference between the two intakes below 5500 was negligible on the street. i premised my earlier response on hood clearance being the most important factor. that said, i did not see a major quantifiable gain in the two intakes for this particular car given the cam's power band. maybe it's been too long that i dont really appreciate how small a performer intake is.

if you can fit the air gap under your hood and you have your heart set on it, go for it.

better?

[patrickstapler]

A little off topic...but a good comaprison nonetheless...even if it is on a X-Brand.

Edelbrock Intake Manifold Dyno Test :: Single Vs Dual + Air-Gap Vs Regular - YouTube

Edelbrock Intake Manifold Dyno Test :: Single Vs Dual + Air-Gap Vs Regular - YouTube

[jdub]

Since they're the same height, I doubt there is much of a functional difference between the AirGap and RPM. Unless the AirGap has part of the divider removed, which I believe on some applications, but not all, it does. Running an open carb spacer would probably accomplish the same goal. I have an RPM with the divider removed and I plan to run an open carb spacer. No Need to get the AirGap- unless I really believe the AirGap feature itself does a lot, which I do not.

My '69 Firebird came with an "airgap" manifold from the factory!

[cavboy78]

I just went through the same thing... If it's the intake you want (it was for me), put it on, add the carb and measure your carb flange to hood height. There is a myriad of drop base heights and air cleaner heights (at least in 14" round) that should get you to where you will clear.

[jdub]

I will say this once again, an SBF AirGap is the same height as a regular old SBF Performer RPM, which people have been running under stock hoods for years.

[Scotti]

Currenty the engine is out of the car so I do not have the option of getting a measurement, in a perfect world I want run the RPM Air Gap, Demon carb and the same air cleaner set up as Jason above under the stock hood.

Jason - beautiful engine and compartment! That is the look I am going for...

[turbo2256b]

Experance with an air gap
I ran 3 intakes on an engine I had. Came with a Performer RPM, Only change I did was pocket port a set of Edelbrock heads pocket ported. Cam was for a marine aplication.
Installed the Performer RPM ran it, then installed the Air Gap ran it. Couldnt tell the differance between them other than the Air Gap cost me 100.00 more than a PERFORMER DID. Yea seat of the pants feel but I been building engines for some 45 years. Installed a Torqer II next. sEAT OF THE PANTS FEEL. It must have added 40 50 HP or more. Even my 12 13 year old son could tell.

[turbo2256b]

Duel planes, I dont care for them a lot. While porting and flow testing my Blue Thunder dual quad intake had a chance to flow test several other intakes. Tested were a Performer, Performer RPM, Torqer II, a Vr Jr with draft removed. Other than the Vr and my blue thunder they were out of the box.

First off the dual planes each port flowed different, The lower ports flowed more averaged than the uppers. Think this is because the upper runners were not as well angled to the ports center line as it tured into the port.
The single planes had a smalerr differance between runners. 4 outer ones a bit worse than the inners but the 4 inners were close to the same as each other. The 4 outers were close to each other.

The Torqer flowed almost the same as the Vr Jr (that had the draft removed).

The Blue Thunder intake flowed stock about the same as the RPM. A bit better on some ports.

All intakes were flowed on my ported DOOE heads they flowed 235 CFM @ about 300 FPS. Also on a Canfield head flowing over 330 CFM.

[09Frank65]

For what it's worth:

I have the air gap manifold with Street Demon carb, no spacer, 2" air cleaner and a Shelby hood. With the hood closed I can see the top 1/2" of the air cleaner.

My guess is that you will need a drop base for the air cleaner. I know with the Street Demon that a drop base won't work but am not familiar with the Street Avenger carb so the fuel hookup and choke linkage may be different.

[ScottsGT]

Ok, I just went down to the garage and put a straight edge across the engine bay at the top of the fender wells. There is 4.5" between this line and the flange on my Air Gap intake.
Now, here's the disclaimer: My front suspension and motor mounts are the Rod & Custom MII set up. They are supposed to be the same exact location as factory.

Since your motor is out, stretch tape across the engine bay like I did, close the hood and going through the radiator opening, measure from the tape up and add that to my 4.5" and you will have total clearance you will need for carb and breather.