Will my RPM Air-Gap Fit under the hood?

[harrellv10 0]

BuckeyeDemon, I can't see your pics on here and I am also too computer illiterate to solve the problem. Could you send pics of the victor junior/shaker set up your described in your post? I am working a similar issude in my 69 mach, 427 FE, victor intake, but using the factory mach 1 scoop with a hole cut in the hood underneath it and a custom ram air base/seal kit from Fastlane Innovations. Curious to see similar setups...

I also have a 1970 Boss 302 that will be getting a shaker breather. I want to use the CHI single plane boss intake on my engine but that intake is TALL! I will use drop engine mounts, but I still think it will be a problem. I'm trying to research the hell out of this before I spend that much money on CHI stuff. Alternatively, I'll just use an Edelbrock E-boss.

[barnett468 418]

On 2/10/2012 at 4:45 PM, Dangstang said:

.I am going to start revising an after market fiberglass shaker assembly with a Air Gap manifold,650 Demon carb.

If you are concerned about hood clearance you can start with the short air cleaner base. The fiberglass mid plates are incorrectly made so you should use a repo steel mid plate.

[BuckeyeDemon 211]

11 hours ago, harrellv10 said:

BuckeyeDemon, I can't see your pics on here and I am also too computer illiterate to solve the problem. Could you send pics of the victor junior/shaker set up your described in your post? I am working a similar issude in my 69 mach, 427 FE, victor intake, but using the factory mach 1 scoop with a hole cut in the hood underneath it and a custom ram air base/seal kit from Fastlane Innovations. Curious to see similar setups...

I also have a 1970 Boss 302 that will be getting a shaker breather. I want to use the CHI single plane boss intake on my engine but that intake is TALL! I will use drop engine mounts, but I still think it will be a problem. I'm trying to research the hell out of this before I spend that much money on CHI stuff. Alternatively, I'll just use an Edelbrock E-boss.

can you weld?

 

[lanky 44]

If you look at the edelbrock website, the 351w versions of the standard RPM and the air gap rpm show the following carb height measurements:

RPM (front of carb base :4.3" , back of carb base: 4.9") 

Air Gap (5.3" and 6.19")

Thats a sizeable difference. Can I ask why no one uses the non air gap version? I actually have one with a summit carb that I haven't installed yet, but reading from people's troubles with the air gap I am sure glad I didn't buy that version. I will be attemping to run a 1/2" spacer but if fitments a problem I might mill the carb base a little. I know I will be looking for a new carb base when install begins.

[BuckeyeDemon 211]

1 hour ago, lanky said:

If you look at the edelbrock website, the 351w versions of the standard RPM and the air gap rpm show the following carb height measurements:

RPM (front of carb base :4.3" , back of carb base: 4.9") 

Air Gap (5.3" and 6.19")

Thats a sizeable difference. Can I ask why no one uses the non air gap version? I actually have one with a summit carb that I haven't installed yet, but reading from people's troubles with the air gap I am sure glad I didn't buy that version. I will be attemping to run a 1/2" spacer but if fitments a problem I might mill the carb base a little. I know I will be looking for a new carb base when install begins.

the air gap on a 351w supposedly has larger runners compared to the standard rpm (unlike the 302 version).

[1969_Mach1 333]

I tried an RPM Air Gap on my 351W many years ago.  I was using the stock hood with the Mach 1 bolt on scoop.  If you are using a carb with a choke assembly you will not be able to get the air cleaner low enough.  Merely because, by the time the air cleaner lid fits under the hood with at least 1/2" clearance, the air cleaner lid will be touching the top of the choke horn or choke plate.  I never ran the motor so I was fortunately able to return the manifold for something else.  If you are using an HP style carb, you might be able to get an air cleaner to fit correctly.

[lanky 44]

Buckeye:  That is the first I have heard of runner size being different between the two. I believe hotrodgarage tested air gap vs rpm and the rpm was only down a few numbers, and they actually were equivalent when they milled the divider on the rpm a little. I can't remember which engine was used during testing, but i would think on most forum guys' motors the difference in performance would be minimal..but hey I am no expert.

[BuckeyeDemon 211]

24 minutes ago, lanky said:

Buckeye:  That is the first I have heard of runner size being different between the two. I believe hotrodgarage tested air gap vs rpm and the rpm was only down a few numbers, and they actually were equivalent when they milled the divider on the rpm a little. I can't remember which engine was used during testing, but i would think on most forum guys' motors the difference in performance would be minimal..but hey I am no expert.

find the article and verify if it was or was not a 8.2 deck (e.g. 302) based manifold.  351w are different.

[BuckeyeDemon 211]

per edelbrock site (note:  the 7181 is the 351w performer RPM):

http://www.edelbrock.com/automotive/mc/manifolds/ford/rpm-air-gap-289.shtml

FORD 351 WINDSOR V8
RPM AIR-GAP 351W (1500-6500 RPM)
Designed for street and high performance 351-400+ c.i.d. 351W Ford V8's, the RPM Air-Gap incorporates the same race-winning design that's been used on our Victor Series competition intakes for decades. The Air-Gap design features an open air space that separates the runners from the hot engine oil resulting in a cooler, denser charge for more power. Larger cross sectional area and a taller carb flange than #7181 for compatibility with large displacement, stroker 351W based engines.

[lanky 44]

Good info to post! Looks like this is the video I remembered

So it was a SBC not ford, but it was a 460hp 360ci with 11.25:1 compression, 292comp cam which isn't small, and 215cc dart heads. I would classify this as a moderate to highly modified street motor. I have no idea if the cross sections were different then or now with SBC stuff. Either way I think it shows most people aren't sacrificing much choosing an RPM on their street motors. With a stroker...probably.

[BuckeyeDemon 211]

12 hours ago, lanky said:

I have no idea if the cross sections were different then or now with SBC stuff. Either way I think it shows most people aren't sacrificing much choosing an RPM on their street motors. With a stroker...probably.

I personally couldn't come to any conclusion with that I test (i'm an engineer so i take very little at face value without fully understanding things).   I see no mention on the edelbrock site about the RPM air gap being larger on the SBC (unlike where for the 351W ford they do).  So basically they could be testing the same manifold (excluding victor).  In addition, the single plane manifolds (e.g. Victor) have a lot of taper in the runner with the exit purposely small so they fit a variety of cylinder heads.  That means when you port match, it's possible to pick up a lot of flow pretty easily.   In that test (unless I missed it), it's unknown if the manifolds could have been holding it back a little bit from their potential due to manifold restrictions.

If the discussion is purely about having the air gap portion (i'm not talking about runner/plenum design but the heating/cooling effect of the air gap), then i think it's silly myself for a street car (yea it can look cool, which i'm fine with).  Removing the water jackets/heat crossover and adding gaps to allow air flow only result in delayed heating.  For a street car, that means the manifold slowly heats up over time changing fuel atomization characteristics and the tune requirements.  For a drag car that only runs a few minutes, that heat soak is much easier to control.  I really didn't see anything in that video trying to control that part of a test either.

 

[lanky 44]

I see your point and don't disagree. On a non stroked *street* 351w running 6500rpm or lower I just can't imagine there is that much more power with the air gap. Just my opinion.

[Alan_Mac 48]

I have a performer RPM on my 418W with a shaker.  As a reference point, It is as tall as you can go with a shaker w/o lowering something.   Back when I built this motor, I had a 780.  I had it on a rear wheel dyno before and after a fairly mild runner flow balancing and size increase.   There was a very noticeable increase in power and the engine sounded louder, like it could breath better.  I think the Performer RPM is a great manifold that can be made even better with a little work. Alan  

[barnett468 418]

The air gap provides more power and better throttle response below around 4000 rpm than any single plane intake on most any engine.

 

 

[harrellv10 0]

BuckeyeDemon, yes, I can weld. From searching the forums, I think a BB breather assembly on the Boss2, drop engine mounts, and milling down the carb mounting base on the intake itself will buy me about about 1.25" to 1.5"

For the Machi 1, I'm pretty sure I can make it work. The Boss is what I'm not sure about. What did you have in mind for welding? 

[BuckeyeDemon 211]

1 hour ago, harrellv10 said:

BuckeyeDemon, yes, I can weld. From searching the forums, I think a BB breather assembly on the Boss2, drop engine mounts, and milling down the carb mounting base on the intake itself will buy me about about 1.25" to 1.5"

For the Machi 1, I'm pretty sure I can make it work. The Boss is what I'm not sure about. What did you have in mind for welding? 

I will dig up the photos and relink.  Give me a few days.  Thanks.

[BuckeyeDemon 211]

some pics i could find.  photobucket killed it....

i also modified the midplate (removed some of the ribs on the sides (can't see under the seal) and modified the front scoop mount (you can't see that either).

that was a 351w, victor jr (i have spaced it back up to original), 1/2 drop mounts and a TKO 600.

basically it was a 428 base, stretched it and installed a drop base that was further modified. 

i also duplicated this on the other forum for reference....

 

[Machspeed 219]

That's a dang shame those pictures are gone, Buckeye. Your build was fascinating and very educational. 

[aslanefe 333]

4 hours ago, Machspeed said:

That's a dang shame those pictures are gone, Buckeye. Your build was fascinating and very educational. 

FYI, on android tablet, I can click on Buckeye's pictures from 2012 (or any picture hosted on photobucket and linked that says 3rd party sharing is disabled) and open them on a new tab and view them. Did not try that on a pc though. Try opening the pictures in a new tab.