mobird

Hey guys, ive done a bunch of research and all ive found is conflicting opinions.

My question is this: can i fit the edelbrock performer rpm air gap with 3/4" adapter and qjet carb under the stock 79 hood with a drop base air cleaner?

If so, can you reccomend me a drop base air cleaner that will give me enough clearance?

Mountainoakie

As the hoods of C3's vary from year to year I suggest you start by putting some modeling clay on the top of your air cleaner then close and reopen the hood so you can measure the amount of clearance you have now.

Then measure the height of your present intake manifold and see how it compares to the height of an Air Gap. Draw a side view picture of what you have now and what you will have with the parts you want and determine if the parts will fit under your hood. All of the parts have height specifications so plug those specifications into your pictures and see how they come out.

BKbroiler

I have an RPM airgap, 3/4 inch high adapter,Qjet and drop base air cleaner with 3 inch element under the hood of my 77. I have the back of the hood raised with washers and I have a flat nut on the lid because a wing nut will hit. It's that close. I also have solid motor mounts because there is no room for engine movement. But it all works great.

mobird

Yikes! Do you have a picture of the hood fitment now that it's shimmed with washers? Curious how much it sticks up.


And if it's not going to fit without modifying the hood, do you think I will lose much performance by going with the performer RPM instead of the performer RPM airgap? I'd prefer the Airgap, but the plain old Performer RPM is available with a Q jet pattern so no adapter would be needed.

MelWff

unless you have done something else to the engine that requires a 6,500 rpm intake go with the performer or performer air gap

mobird

Well it's more about planning for the future. I plan to eventually make it a 383 stroker, and I'm working on getting new heads/longtube headers right now so from my research I would benefit from the added plenum volume that the RPM line provides.


I'd like to run the RPM airgap if at all possible, but if I can't, I'll run the performer RPM.

MelWff

I'm getting a little confused by the names you are calling the manifolds. There is the Performer, the Perfomer Air Gap, the Performer RPM, and the RPM Air Gap. The last two are the exact same height and are the 6,500 RPM manifolds and are square bore. The first two are the spread bore pattern with a 5,500 RPM figure and roughly 1" shorter.

http://www.edelbrock.com/automotive/mc/manifolds/chevy/

Jebbysan

Just run the 7104 Performer RPM Q-Jet manifold.....
Unless you have to have the looks of the "Air Gap" because it gives absolutely zero benefit at all.
All intakes heat soak until they are all even in temperature across the whole part...Air gap or not.....
Hot Rod and Super Chevy proved that the runners between the two show zero advantage as well.
Not only that....but a Q-Jet to Holley spacer is a horrible mismatch in a four hole design.....an open one is not that bad....but divided plenum dual plane manifolds do not like open spacers......

http://www.summitracing.com/parts/EDL-7104/

Jebby

cv67

No
Planning for the future is good and all but put what works good on there today so you can really enjoy it. Most need less intake than they think they do

mobird

Huh, thought the RPM Air Gap was still called the "Performer RPM Air Gap". Oh well, it's pretty obvious what I meant.

Yeah I realize that both of the RPM intakes are the same height, however since I"m running the Qjet I would need a carb adapter to run the RPM Air Gap, which would require another 3/4" of hood space. The Performer RPM is available with a spreadbore pattern so I wouldn't need a carb adapter. I would prefer to run the Air Gap, but if I can't fit it under my hood (due to the required adapter with my carb) then I'll just run the Performer RPM.

mobird

Thanks for the info! I don't care too much about the looks of the Intake manifold.

And thanks for bringing that to my attention, I didn't think about how the spacer could affect the performance.

Sounds like I might as well just go with the 7104 and a drop base air cleaner.

BKbroiler

You can see here the hood is raised maybe 3/16 ".

BTW - my adapter is the "open" type

cooper9811

Jebby is right - I ran both on my old 383 and 406 at different times and felt no real difference in overall performance. If you measure the cross section of the runners they are very close. Runner length might be different, but the cross section of the ports coming out of the intake are so close it's negligible. I also seem to recall the 7104 may have idled a little better on the first start, I suspect because it warmed up the carb and helped atomize the fuel faster. After running the engine for a while I don't recall any difference in performance.

drwet

I would be interested in seeing those tests that show no advantage to the Air Gap. I've seen a number of articles over the years that show a power advantage to the Air Gap design. Modest, but an advantage nonetheless. In my case the Air Gap was an improvement as I was having major heat soak problems until I installed the Air Gap. (Yes there were other mods done at the same time so it wasn't just the manifold, but it was part of the solution.)

mobird

Thanks for all the input guys. I think im gonna go with the performer RPM since all it should require is a drop base air cleaner, and it should perform almost the same as the air gap.

71454Chevelle

You will get the same affect as the RPM Airgap if you use the Performer RPM Q-Jet and install intake gaskets that block off the exhaust crossover and install a lifter valley shield. The runners aren't kept isolated, but you will keep the exhaust heat and hot oil off of the bottom of the intake.
Also, IMO you'd be better off NOT running an adapter between the carb and intake. Anything you "may" gain from the airgap design would most likely be lost in using an adapter.

mobird

Where would I find a gasket that block off the exhaust crossover? I'm most likely ordering from Summit, so if they sell one, could you point me in that direction? And I'll probably take your advice on the lifter valley shield!


Yeah I'm thinking the same on the adapter. Thanks!

GUSTO14

I found this on JEGS, but Summit should carry the same set. The block-off plates are the rectangular pieces at the bottom with the raised round center.

Mr. Gasket 101B - Intake Manifold Gasket Sets
Performance Material
1955-91 Chevy 262-400 V8
Thickness: .060''
Rectangular Port Size: 1.25'' X 2.00''

http://www.jegs.com/i/Mr.+Gasket/720/101B/10002/-1

Good luck... GUSTO

mk's78

I use Play Dough and it works great...mike