Edelbrock, Perf Air Gap vs RPM, Vs RPM Air Gap??

[F-BIRD'88]

We once tried to build a set of dual tube water jacketed long tube raceing marine sbc headers...
I know what you are up against.. We got over 525 hp from a vrry hot 355 sbc on methanol...

Actually it was a pair of 355 's on meth 13:1 cr... 000++ hp.. Them used vic jr's but were reving to use that well. 6700-6800 rpm wot..

A bit high for a jet drive setup..

[F-BIRD'88]

A blown 383 would be good on a jet drive.

[GARY C]

Right now I'm putting together a 383 Chevy for a customer with a jet boat. I didn't build the engine originally but I'm getting to do a few upgrades along with the rebuild. Anyway I'm thinking about the intake manifold and I think it is something I'm going to test out on the dyno. Right now the customer has a Performer Air Gap intake and I'd like to try an RPM and or an RPM Air Gap and maybe a Victor Junior to see what runs the best in the 3000 to 5500rpm band.

I don't think I've ever really looked at a Performer air gap before but is it the same as a Performer except for that feature as I've heard the Perf RPM and the RPM Air gap are actually identical inside...

With those cubes and that RPM range the RPM Air Gap and the V Jr will show the best average #'s it would be interesting to throw the cheap Professional Products Hurricane in the mix, small runner Bow Tie design. https://www.summitracing.com/parts/pfs- ... l-products

[F-BIRD'88]

Just like on the intake, on the exhaust side the camshaft that works best with dyno headers will not be the same best power cam that is best with the Marine manifolds.
The whole induction.--exhaust -- camshaft system has to all work together as a system.
Each part of the whole effects the other elements in the system.

[DaveMcLain]

I was finally able to do some of this testing today and I ran the engine on the dyno using the boat headers. The best combo on the Performer Air Gap(Non RPM) was 445 horsepower and 490lbs/ft. With the Performer RPM(non air gap) the engine made 465 horsepower and 500lbs/ft torque. The Performer RPM liked by "hybrid" spacer with an oval on one side and two holes on the other whereas the Performer Air gap very slightly preferred an HVH merge over an open.

I have not run a Victor Junior yet but I did get to test a GM Bow Tie single plane that was taken off of a 604 crate engine. That intake managed to make a max HP of 468 which was three horsepower better than the RPM but it sacrificed 20lbs/ft torque around the peak to make that happen and it was much more fussy about the choice of carburetor spacer really only running well with a 1 inch open.

[bigjoe1]

Your results are very similar to what I have seen too



JOE SHERMAN RACING

[F-BIRD'88]

Now retard the camshaft installed position a bit.
It will (with the Perf RPM intake), meet or exceed the peak power of the single plane test all while still making more peak torque and more average torque with the High rise dual plane over the single plane (on this motor). Try a bigger carb too.
Good to see the effect of the hybrid carb spacer on the high rise dual plane
. How much low rpm torque did the open spacer give up to the hybrid spacer?
The dual plane can probabily use a bigger carb and may/should also pick up a few peak rpm ponies with a cam phasing adjustment.

[DaveMcLain]

Now retard the camshaft installed position a bit.
It will (with the Perf RPM intake), meet or exceed the peak power of the single plane test all while still making more peak torque and more average torque with the High rise dual plane over the single plane (on this motor). Try a bigger carb too.
Good to see the effect of the hybrid carb spacer on the high rise dual plane
. How much low rpm torque did the open spacer give up to the hybrid spacer?
The dual plane can probabily use a bigger carb and may/should also pick up a few peak rpm ponies with a cam phasing adjustment.

I doubt I'll mess with the cam timing but I might experiment to see what it does with my 1050 on top of a divided adapter instead of my current 950HP.

The cam I put in the engine is using the GM "hot cam" exhaust lobes 228 degrees at .050 on both sides ground on a 104 lobe sep in on 103 with a 1.6 rocker. I've used a similar cam in this sort of build before and it worked well while being easy on the valvetrain. Its interesting in how the engine sounds pretty feisty while idling at about 1000 rpm but cleans up and gets on the cam very quickly and sounds really great pulling about a 50 horsepower load at 3000rpm.

[cjperformance]

I was finally able to do some of this testing today and I ran the engine on the dyno using the boat headers. The best combo on the Performer Air Gap(Non RPM) was 445 horsepower and 490lbs/ft. With the Performer RPM(non air gap) the engine made 465 horsepower and 500lbs/ft torque. The Performer RPM liked by "hybrid" spacer with an oval on one side and two holes on the other whereas the Performer Air gap very slightly preferred an HVH merge over an open.

I have not run a Victor Junior yet but I did get to test a GM Bow Tie single plane that was taken off of a 604 crate engine. That intake managed to make a max HP of 468 which was three horsepower better than the RPM but it sacrificed 20lbs/ft torque around the peak to make that happen and it was much more fussy about the choice of carburetor spacer really only running well with a 1 inch open.

Ah good results, just what I thought re the RPM! Did you run exhaust crossover heat or not?
When you tried the hybrid spacer did you have the oval over the shallow side plenum

[DaveMcLain]

No exhaust heat crossover used. I placed the oval over the top/high plenum and the two holes over the deep/low side.

[cjperformance]

No exhaust heat crossover used. I placed the oval over the top/high plenum and the two holes over the deep/low side.

Yes good stuff. Great testing there.
Some exhaust heat would be nice at low rpm & throttle but depends how this will be used.

[Warp Speed]

This is a jet boat, and you only really need to worry about a fairly narrow power band. Depending on rpm desired (It will be a combination of engine output and impeller size) tune for best power in this range +/- 250rpm.
Steady state testing is how this should be done, as that is how it will be in the boat.

[Warp Speed]

Depending on the power level , there is very little difference in all of them




JOE SHERMAN RACING

Your results are very similar to what I have seen too



JOE SHERMAN RACING

So 20hp and 10lbft between manifolds is "very little difference"?!? Lol

[F-BIRD'88]

Depending on the power level , there is very little difference in all of them




JOE SHERMAN RACING

Your results are very similar to what I have seen too



JOE SHERMAN RACING

So 20hp and 10lbft between manifolds is "very little difference"?!? Lol

When used in a boat, on the water, all said and done, yes 20HP is a very small difference. The boat top speed difference will be barely detectable/measureable.
Boat drive trim and in this case Jet drive nozzle/jet impeller design will make more difference.

Similar: boat prop design. 20HP is nothing on water.

But on water, a strong overall engine torque curve (more so critical with a prop than with a jet drive) helps the boat accelerate and get up on plane better. Think of a boat much like a car always going up a steep hill and having only one transmission gear ratio to work with.

[Warp Speed]

Depending on the power level , there is very little difference in all of them




JOE SHERMAN RACING

Your results are very similar to what I have seen too



JOE SHERMAN RACING

So 20hp and 10lbft between manifolds is "very little difference"?!? Lol

When used in a boat, on the water, all said and done, yes 20HP is a very small difference. The boat top speed difference will be barely detectable/measureable.
Boat drive trim and in this case Jet drive nozzle/jet impeller design will make more difference.

Similar: boat prop design. 20HP is nothing on water.

But on water, a strong overall engine torque curve (more so critical with a prop than with a jet drive) helps the boat accelerate and get up on plane better. Think of a boat much like a car always going up a steep hill and having only one transmission gear ratio to work with.

We are talking jet boats here, very narrow rpm band. And any gain of 20hp for a couple hundred bucks or less is a good gain. IMO

So what is a descent gain between manifolds if 20hp isn't?!? Lol

BTW, have you ever owned a jet boat?
And thanks for answering for Joe...........