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DUAL PLANE VS SINGLE PLANE INTAKE:
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jeep_406
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1972 Chevrolet Nova

PostPosted: Sun Sep 17, 2006 8:32 pm    Post subject: DUAL PLANE VS SINGLE PLANE INTAKE: Reply with quote

Wondering if I might run better times with an RPM Air Gap intake on my 406 smallblock. I'm currently running a Bowtie Victor Junior that I matched to my cast Sportsman II heads.
Intake flows 255 @ .550 lift
Exhaust 201.8 @ .550 lift

10.14 compression

Extreme Energy 284 Hydraulic flat tappet cam with 1.6 rockers
.541 intake
.544 exhaust
284 intake
296 exhaust
110 lobe sep
set up straight up

3310 Vacuum carb flows 834 cfm

MSD 6AL

700R4 with Precision Industries 3200 stall converter.

4.11 12 bolt Eaton Posi, Moser axles

Mickey Thomson E.T. Streets.

Car weighs 3750 with my husky toddler ass Strapped in the seat.

Best run this year with this package=12.08 @ 110.95MPH through the exhaust. Engine seems to like shifting at 7000RPM 1st - 2nd. 6500RPM into 3rd.

The RPM intake is supposed to be better through the mid range to 6500 over the Victor JR.

Any thoughts?



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Big Dave
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PostPosted: Sun Sep 17, 2006 9:01 pm    Post subject: Reply with quote

The dual plane magnifies the signal to the carb by isolating half of the runners from the others. This is important with a late closing intake point on your cam (if chosen for either the rump-itty rump or to bleed off static compression so you can run pump gas). It works by pairing cylinders so that it cuts the amount of reversion in the intake manifold in half, which yields a stronger more consistent signal to the carburetor.

The trade off is the runners are longer (more bottom end torque) which results in more fluid friction, and they are bent (to make them fit between the valve covers) so there is less of an opportunity to develop laminar flow; and characteristically the runners are of a smaller diameter than the Victor Jr. so the total flow rate is less (but it does increase the port velocity by restricting port volume).

I personally run a RPM Air Gap because for the percentage of time I spend above 5,800 RPM is small compared to the amount of time I spend cruising. I still get from my SBC 406 524 peak horse power and 486 average horse power with this manifold (I also have Victor Jr. heads, a roller cam and a Holley HP carb on top).


Big Dave
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jeep_406
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1972 Chevrolet Nova

PostPosted: Sun Sep 17, 2006 9:50 pm    Post subject: Reply with quote

I chose the cam to bleed off compression so I could run pump gas. Do you think the added low to mid range would make up for flow loss above 6500RPM.

I'm only briefly above 6500 at the top of 1st gear.

I don't screw with the car on the street. The only time it's at WOT is at the strip but I go to the track 20-25 times a year.
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af2
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1933 Willys Coupe

PostPosted: Sun Sep 17, 2006 11:52 pm    Post subject: Reply with quote

jeep_406 wrote:
I chose the cam to bleed off compression so I could run pump gas. Do you think the added low to mid range would make up for flow loss above 6500RPM.

I'm only briefly above 6500 at the top of 1st gear.

I don't screw with the car on the street. The only time it's at WOT is at the strip but I go to the track 20-25 times a year.


If it is better. Please let me know! My set up is not doing it!!!
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jeep_406
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1972 Chevrolet Nova

PostPosted: Mon Sep 18, 2006 10:28 am    Post subject: Reply with quote

I just got off the phone with a tech at Edelbrock. He didn't think there would be a significant change going to the RPM Air Gap over the Victor Jr because of my engine size and the RPM range.
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jhyjohnson
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1973 Buick Apollo

PostPosted: Mon Sep 18, 2006 11:03 am    Post subject: Reply with quote

i swapped to the rpm air gap from torkerII on my 355smallblock and actually lost .25 seconds in the 1/8th. swapped back to the torkerII and 2in spacer and ran faster than ever. just my experience.
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Big Dave
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PostPosted: Mon Sep 18, 2006 3:09 pm    Post subject: Reply with quote

Like I said: the dual plane will make a difference on the street. For all out competition you want a Tunnel Ram like af2 has as it acts like Individual Runners (not very tunable though) at Wide Open Throttle, or the small plenum version of the tunnel ram which is the single plane. The reason that a spacer under the carb helps on a large single four barrel carb on top of a single plane is that it increases the plenum volume to more closely approximate the tunnel ram.

af2 you might want to try putting blocks of wood between the four barrel pads on the tunnel ram to reduce the plenum volume (do not block off the vacuum signal of the other four cylinders to both carbs in the process though; a small block of wood with a large 1" hole and add to the thickness of the block to restrict volume), or you could add two carb spacers of varying thickness to increase the volume. A true IR velocity stack you tune by varying the length of the tube.


Big Dave
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clay
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1972 Chevrolet Nova

PostPosted: Mon Sep 18, 2006 6:26 pm    Post subject: Reply with quote

I would think the crossover point is too high in the rpm range for the AirGap to benefit your setup. From the tests I have seen the AirGap wins torque by 20 - 30 ft. lbs. below the 4000 or so point and loses around 10 - 15 h.p. by 6000 rpm or so. I'm sure you don't drop back down to a rpm where the AirGap would benefit on the shift. Clay
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GrandSportC3
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1968 Chevrolet Corvette

PostPosted: Tue Sep 19, 2006 6:54 am    Post subject: Reply with quote

I'd stay with the Victor Jr. for that setup! If you'd have the Victor Jr. ported and matched to the heads, you'll pick up some power!! I personally really dislike dual plane intakes.. If I have any engine built with above stock output, I always want the single plane intake..
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jeep_406
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1972 Chevrolet Nova

PostPosted: Tue Sep 19, 2006 7:59 am    Post subject: Reply with quote

I ported and matched the Victor JR intake to my Sportsman II heads which I also massaged.
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cutlass389
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1978 Oldsmobile Cutlass

PostPosted: Tue Sep 19, 2006 6:27 pm    Post subject: RPM's? Reply with quote

Pardon my lack of knowledge Embarassed, only you know what works best on your setup, but from my reading-200cc runners and 284 degrees (232ish @ .050) feeding that many cubes shouldn't want to rev that high. Obviously I'm missing something (story of my life). Didn't Paul P. find less e.t. when he lowered his shift point recently?
Also I've read the same results as Clay with Edelbrock single vs. RPM dual.

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af2
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1933 Willys Coupe

PostPosted: Tue Sep 19, 2006 7:32 pm    Post subject: Reply with quote

Big Dave wrote:
Like I said: the dual plane will make a difference on the street. For all out competition you want a Tunnel Ram like af2 has as it acts like Individual Runners (not very tunable though) at Wide Open Throttle, or the small plenum version of the tunnel ram which is the single plane. The reason that a spacer under the carb helps on a large single four barrel carb on top of a single plane is that it increases the plenum volume to more closely approximate the tunnel ram.

af2 you might want to try putting blocks of wood between the four barrel pads on the tunnel ram to reduce the plenum volume (do not block off the vacuum signal of the other four cylinders to both carbs in the process though; a small block of wood with a large 1" hole and add to the thickness of the block to restrict volume), or you could add two carb spacers of varying thickness to increase the volume. A true IR velocity stack you tune by varying the length of the tube.


Big Dave



Dave I read this post about 5 or 6 times. The only thing I can come up with is a smaller hole! or carb!!! From what is wrote. Confused
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Big Dave
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PostPosted: Tue Sep 19, 2006 9:08 pm    Post subject: Reply with quote

Standard modern Tunnel Ram has a base manifold with eight individual runners, then the top part bolts on as either a one piece; or a two piece with alternate carb configurations.

If a two piece top is used you can not only use any carb set-up offered (generally two small fours, or one moderate sized four, or one humongous four). Another advantage of the two piece top is you get to play with the plenum chamber beneath the carbs increasing or decreasing it's volume dependant upon the RPM characteristics of the motor, and size of the CFM rating of the carb(s) chosen.

The purpose of the plenum is to allow more than one throttle bore of the carb to feed a hungry intake runner at WOT. (The demands in terms of cfm per runner often exceed the cfm of the individual throttle bore placed above an intake runner (total cfm of the carb divided by four for most Holley square bore carbs).

Example (pulled out of thin air; your situation may vary) you have a BBC Dart head that flows 360 cfm per intake port. Well one throttle bore of a 660 cfm Holley carb on top of a tunnel tam over that intake runner would suck up all of the 165 cfm that the throttle bore could supply (matter of fact it wants more than two of the carb's bores to meet it's demand). The plenum beneath the carb allows that intake port, starving for a fresh charge, to suck on all four bores of that 660 cfm carb simultaneously. If the plenum were too small (restricting access the 660 cfm Holley on top of the tunnel ram) it would run out of carb. You would know you have run out of carb from the car's reaction; so you slap on a bigger cfm carb to correct this problem (We all know how cheap carbs are so changing them isn't a problem; and we all know how quickly we can over carb an engine, and what happens when we do).

If on the other hand we are running a small inch motor with a product developed for a larger cubic inch engine (say a 301 SBC using a manifold designed to support a SBC 427 at WOT) then we might find our selves with a plenum that is so big the vacuum signal from the intake port gets dispersed crossing the chasm of the plenum and the carb doesn't see the need to supply all the air and fuel the engine wants. This results in a flat, soggy throttle with a lean running engine, that no amount of richening of jets can fix (matter of fact you will see it start to flood the cylinder and extinguish the flame front with raw gas going down the header tube). By restricting the plenum size you increase the signal to the carb and get better throttle response and better combustion.

It is the fine art of deciding what size plenum for a given carb and engine that keeps the cloth covering the Pro Stock intake manifolds (usually one of a kind custom sheet metal Wilson's) from prying eyes between rounds. This is one area of the engine tune that Warren will not talk to Greg about while standing in line on race day buying coffee and donuts on the way to the track (unless maybe it was to offer his opinion that he should run a QuadraJet on a cast iron oval port manifold).


Big Dave
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af2
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1933 Willys Coupe

PostPosted: Tue Sep 19, 2006 9:39 pm    Post subject: Reply with quote

#6 I see what the hell you are saying. Any chance I could get you're ass to the west coast and help!!!! I'll pay the pit pass. Shocked
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jeep_406
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1972 Chevrolet Nova

PostPosted: Tue Sep 19, 2006 10:33 pm    Post subject: Reply with quote

Cutlass 389,

When I first put my car together I was thinking that I would be shifting around 6200RPM but it has run quickest when I've gone to 7000 RPM in first and 6500RPM in second gear.
What surprises me about the RPM level is that I'm running through 1.75 Hooker headers into a rather restricted 2.5 inch exhaust. Last runs I made in 2005, I dropped the exhaust and picked up almost two tenths.
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