Has anyone tried a RPM Air Gap on an otherwise stock HP500
 

If so please post the results.

I read on another Forum, where a gentleman had a 502, Crane 731 Camshaft, HP 500 heads, with a aluminum dual plane intake. Then switched to a single plane dart like the HP500 has.

Dual plane = 459HP/482FT lbs at 5000RPM.

Single plane Dart = 487HP/511FT lbs at 5000RPM.

I'd be shocked if an Edelbrock Air gap made more power over your Dart Single plane to make your boat go faster. The air gap design works well in cars where the engine gets heat soaked. In a boat, I don't see that really being a problem, especially with the factory oil splash shield under the intake. Considering it would probably take 20-25HP per engine to gain 1mph in a 36 Outlaw, I'd leave it alone.

There might be some others here who have experience in this swap.

In most cases the single plane intakes are made for 4000rpm and above. They are slower on hole shot and make up for it on top end power. I would agree with mild thunder on this. U most likely wont see very much diff if at all!!

id say the edelbrock air gap vs the dart single plane that comes on a hp500 would produce almost identical results.if anything the dart manifold would make a few more hp but not enough to notice in the boat.

I am in agreement that the dart may have the slight edge on top end at 5000+ RPM.
I spend most of my time around 3500-4000 and am thinking the Air Gap may or should have the edge there because it should build more torque in the mid range.

GB, this thread has been referenced before, and since the test was on a 454 it is not exactly apples-oranges, but it does show that a dual plane intake like the Air Gap will give you a decent amount more torque through the mid range. Will that be enough to tell a difference in a boat? Who knows? Maybe that would allow you to go up in pitch on your prop for better cruising speeds, but probably at the expense of top end speed.

http://www.carcraft.com/techarticles...r_numbers.html

(as an aside - the article mentions that they were able to use the same pushrod length going from the stock cast iron to the AFR's, and I would love to see how that could be true with the thicker deck on the AFR heads. AFR suggests a 0.25" pushrod may be required going from stock, so I have to wonder how they got their geometry squared away.)

Your question is timely for me, as I am also trying to decide between an Air Gap and a Dart oval port to run with my AFR 265's on my 489. I have a number of questions that I need to answer before making the decision, so I was thinking about starting a separate thread.

Also, keep in mind that you may have to address jetting changes in the carb when switching to a dual plane. Merc came up with the staggered jetting on the HP500 specifically to deal with the fuel distribution issues of the single plane Dart manifold. This might have to change when you switch to the dual plane.

If you decide to make the switch, I have an Air Gap for rectangle port heads that I am not using. It is in good shape - just needs a little minor cleaning up. I can't use it with my oval port AFR's, so it is not doing me any good sitting around. I work in Louisville, so I'm close to you. PM me if you are interested.

Switched to the Air Gap on my carb 502's and did not notice much difference, maybe a touch more midrange.

Here's one of the questions I wanted answered to help me with my decision: Is a dual plane manifold a hedge against reversion? My thinking would be that it could help because you would have a stronger signal and more intake charge velocity at lower engine speeds. So if you had an engine on the ragged edge of reversion, maybe it would help in that respect.

GB, I don't know if I would swap out the manifolds on an engine that is running fine as is, but if you are pulling them down anyway for a top end rebuild or something like that, you might take the opportunity to try it with the AG's.

I have yet to splash my new 502 build but I chose the air gap as the best overall combo for me. With 320cc rect port intakes I ported the manifold runners to the fel-pro intake gasket and removed quite a bit of material. I also am using a 1" open spacer to increase the plenum volume a bit in an attempt to get the power to hang on a little longer at higher rpm's........ I will be spending most of my time around 3700/4000 rpm and the air gap is at least 20HP/TQ stronger than a single plane in that range.........
I can't post a pic from my IPad now but if you want to see how much material is removed from an air gap intake ported to the fel-pro 1275 gasket look here..... TBF

http://www.offshoreonly.com/forums/g...ml#post4025752