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-   -   Edelbrock RPM versus Air Gap RPM (http://www.hotrodders.com/forum/edelbrock-rpm-versus-air-gap-rpm-225216.html)

Too Many Projects 10-20-2012 07:10 PM

Edelbrock RPM versus Air Gap RPM
 
Is there enough difference in street performance between these 2 intakes to justify spending almost twice as much for an used air gap versus a non-air gap...:confused:

vinniekq2 10-20-2012 08:00 PM

both are very good medium power manifolds.The difference between them is small

hcompton 10-20-2012 08:34 PM

Air gap is proven performer. But install hight is pretty high better check clearance.

A magazine test the air gap against another manifold.
Edelbrock's Air Gap Performer Intake - Tech - Popular Hot Rodding

xxllmm4 10-20-2012 09:46 PM

This pretty much sums it all up...
However, for a street driven car the standard RPM is a better choice, they heat up a lot faster.

cobalt327 10-21-2012 03:40 AM

Quote:

Originally Posted by Too Many Projects (Post 1601295)
Is there enough difference in street performance between these 2 intakes to justify spending almost twice as much for an used air gap versus a non-air gap...:confused:

In a word- no. The non air gap is within a very small percentage of the air gap, and the major reason for the difference is not the air gap but the sliced out plenum divider that gives the air gap a slight advantage at the top of the rev band- where the engine is at a very small percentage of the time unless the vehicle is race-only.

If you plan to drive the vehicle in a cold climate, the air gap is even less of an advantage. It takes longer to warm up and the choke on the carb will be needed for a longer time. That can increase emissions, hurt mileage, and wear the cylinders and pistons/rings faster. This is slightly less of an issue if Vortec heads are being used; they do not have any heat cross over to warm the plenum anyway. But the splash from the lifter valley isn't able to help warm the intake on the air gap intake, so it's still gonna take longer to stabilize temps using the air gap on Vortec heads.

BTW, the air gap and non air gap RPM intakes are the same height.

Too Many Projects 10-21-2012 08:53 AM

Thanks for all the feedback. I will persue finding a standard performer rpm..:)

toddalin 10-21-2012 11:31 AM

I run the Performer RPM with a 1/2" open spacer. My mechanics used to say that the spacer is better than the cut down divider because it adds plenum volume and is easily "reversable." I also blocked off the heat riser and made a "lifter valley splash shield" to keep the hot oil off the manifold's bottom.

It is also port matched and the interior walls and divider were hand "contoured" to remove casting flaws and bumps. I would bet that it now flows as much or more than the air gap.

Even more "blending" was performed after these pics were snapped. (I can get anal about such things.) It only takes some sandpaper and time.

http://www.largescaleonline.com/eima...racket_104.jpg
http://www.largescaleonline.com/eima...racket_103.jpg
http://www.largescaleonline.com/eima...racket_102.jpg
http://www.largescaleonline.com/eima...racket_101.jpg
http://www.largescaleonline.com/eima...racket_100.jpg

malc 10-21-2012 12:14 PM

I like the smoothing out youve done, Ill be doing that to mine next time its apart.
Im using a 2" spacer on my Airgap, runs just great, no issues with climate as its never that cold here where I live in Spain.

http://www.hotrodders.com/gallery/da...nch_Spacer.jpg

oldbogie 10-22-2012 12:03 PM

Quote:

Originally Posted by Too Many Projects (Post 1601295)
Is there enough difference in street performance between these 2 intakes to justify spending almost twice as much for an used air gap versus a non-air gap...:confused:

If this is a street driven vehicle with street gearing use either the Performer or for a little more top end emphasis the Performer RPM.

The Air-Gap is strictly a high RPM manifold, not that it delivers so much more power but rather without manifold warmth to vaporize the fuel as in the Performer/Performer RPM the Air Gap needs high port velocity to mechanically rip the fuel into a vapor state. So the Air Gap requires very rich mixtures in cool to cold weather when street driven as well as in wet humid weather has icing problems that jam the throttle butterflies and plug the intake as well as allowing breaking off ice chunks to enter the engine. The extra rich mixture alone greatly shortens engine life by washing away the upper cylinder lube.

The advertiser give you half the information you need to decide about these things, while it's true that a cold thus dense mixture packs more molecules into the cylinder, the fuel has to be vaporized and well mixed to burn. Inside a manifold there is a lot of mayhem and amazing amount for such a short distance but this is why port fuel injection is so superior in making power than a carb or TBI as this mayhem is eliminated. The finely vaporized fuel the carb or TBI puts into the airstream quickly comes out of suspension with the air and becomes streams of liquid running along the outside of every turn the mixture has to make. This stream if not remixed does not burn, it just gets pumped around the rings to enter the crankcase and gets tossed out the exhaust valve. That's lost power and lost money. The answer to this was to just richen the mixture till a good burnable mixture can be achieved to run on and just let the excess go as I describe. Modern heads put a lot of effort into wet flow in order to understand what combustion chamber shapes help re-mix the liquid flow with the air flow, this being the foundation of performance and mileage seen with the GM Vortec, Ford GT40, and Chrysler Magnum heads. This technology being driven from the EPA in its attempt to clean up the exhaust and improve mileage. The technology actually goes back to the work of Sir Harry Ricardo from the 1930's. Except for old man Henry Ford, this work was ignored by Detroit as they would not pay the royalties for these patented combustion chambers. The flat head used this technology for many years and Ford carried into the early Y Blocks, but when the wiz-kids took over they wouldn't pay the royalties so the heads got simpler and more fuel hungry. Chevy actually walked a real thin line on the new SBC for a lot of years with the double quench head, right on the edge of the Ricardo patents just short of a law suit. Everybody else took a path far away from the Ricardo chamber throughout the 1970s and 80s until finally emission and mileage mandates drove them into the Ricardo chamber. You see it coming at GM on the SBC with the L98 and the Swirl Port where double quench is reintroduced and the spark plug moves up to the valve tangent line so the burn has less distance to travel this is faster to complete. It comes in pretty fully with the LT1 and LT4 heads of the mid 90s where a bench extends from the spark plug to the exhaust valve side restoring the quench on that side while the intake feeds into a relief cut into the old quench pad on that side of the plug with sharp edges leading to the spark plug which is intended to remix the wet flow running on the long side port turn with the air flow that can and does turn in at a sharper angle than the wet flow. This is really needed with port injection above the valve but also does wonders for undoing fuel separation on conventional carb and TBI manifolds. The LT1/4 chamber shapes later in the 90's appear on the L31 Vortec and the aluminum Fastburn heads for conventionally cooled engines.

This of course has nothing to do with port efficiency; the truth is you need both excellent porting and combustion chamber configuration. So there are heads out there that breathe better but don't burn as well, and heads like the Swirl Port that burn pretty well but don't breathe. There are lots of engines that got one Oldsmobile for example rather a prototype for the SB2 port layout and not the other with big open chambers having the spark plug off in Siberia.

So the fact is that vaporized fuel burns and liquid does not, so before you worry about cold high density air you've got to worry about how to mix the fuel into it. The factory uses heat because most engines are used at low RPMs, the hot rod industry seizes this opportunity to generate big power numbers but doesn't tell you that without super high RPMs to rip the fuel into vapor you will need to run so rich that engine life is seriously degraded especially in cold wet climates.

Bogie

AutoGear 10-22-2012 12:17 PM

Bogie;

Thats all great but what about the 'Tornado' devices that help "straighten out" the airflow, before it hits the floor of the plenum and makes a few 90* turns???
The guy on TV said they're great.

All kidding aside; Thats probably the best post in terms of the nuts and bolts of what a combustion chamber does and how it works in conjunction with the rest of the cylinder head and the intake manifold.

toddalin 10-22-2012 01:10 PM

Quote:

Originally Posted by oldbogie (Post 1601918)
Inside a manifold there is a lot of mayhem and amazing amount for such a short distance but this is why port fuel injection is so superior in making power than a carb or TBI as this mayhem is eliminated. The finely vaporized fuel the carb or TBI puts into the airstream quickly comes out of suspension with the air and becomes streams of liquid running along the outside of every turn the mixture has to make. This stream if not remixed does not burn, it just gets pumped around the rings to enter the crankcase and gets tossed out the exhaust valve. That's lost power and lost money. The answer to this was to just richen the mixture till a good burnable mixture can be achieved to run on and just let the excess go as I describe.
Bogie

Can't agree with this and neither CarCraft Magazine through their dyno testing.

Carbs continue to make more power than port injection. This is because the fuel is introduced further upstream. The fuel then pulls the heat out of the air as it vaporizes in the manifold and this results in a cooler, denser mixture and more power.

hpete 10-22-2012 02:03 PM

Carbs make more power in a controlled environment but when it's 10 below and you need to get to work tbi is better than a carb and direct port is better than either one. Efi moters run better in changing weather, burn less fuel, pollute less, and last longer than carb motors. I've read car craft since I was 12, I'm now 53 those guys invariably do something during a dyno test that skews the results, large tube headers on a stock budget motor, vic jr on stock heads etc. It's not just them it's mags in general. Take them and this with a grain of salt.

Silver Surfer 10-22-2012 02:44 PM

Quote:

Originally Posted by toddalin (Post 1601939)
Can't agree with this and neither CarCraft Magazine through their dyno testing.

Carbs continue to make more power than port injection. This is because the fuel is introduced further upstream. The fuel then pulls the heat out of the air as it vaporizes in the manifold and this results in a cooler, denser mixture and more power.

I think the key here is that carbs make higher PEAK horsepower, but as far as power under the curve, port injection makes more power.

toddalin 10-22-2012 02:59 PM

Quote:

Originally Posted by Silver Surfer (Post 1601970)
I think the key here is that carbs make higher PEAK horsepower, but as far as power under the curve, port injection makes more power.

Don't be so sure about that until you read this article with dyno tests. Carb pretty much beat port injection from their start point of 3,000 RPM up the band.

Quick Test: Carbs Vs. Fuel Injection On Holley

oldbogie 10-22-2012 03:08 PM

Quote:

Originally Posted by toddalin (Post 1601939)
Can't agree with this and neither CarCraft Magazine through their dyno testing.

Carbs continue to make more power than port injection. This is because the fuel is introduced further upstream. The fuel then pulls the heat out of the air as it vaporizes in the manifold and this results in a cooler, denser mixture and more power.

Yeah well running an engine in a Los Angeles dyno room ain't the same as getting groceries on a December day in Minneapolis.

Stick around we'll make you smarter than Car-Craft can imagine, we’re just here to increase your knowledge base without the prejudice of trying to sell you something.

In the mean time re-read what I wrote, I didn't dispute the colder yields more power, I just put in the real world provisios that you gotta live with when you do this to a daily driver. Provisios that gets omitted in the advertising copy.

I've often considered that the hot rod manufactures like Edlebrock miss an opportunity selling manifolds like the Victor Jr. which really works well except during that time and place where there's real winters. Imagine a Victor Jr. choice that's has the valley closed around the runners so it can get warm and sold as a year around high performance street manifold. You reading this Vic Jr.?

Bogie


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