Dual Plane Center Divider

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Dual Plane Center Divider

Post  Doug Rahn on March 22nd 2018, 1:21 pm

Is there any significant advantage in cutting down the plenum center divider some?
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Re: Dual Plane Center Divider

Post  dfree383 on March 22nd 2018, 2:04 pm

It’s pretty old school, but does help a little top end.

Got pleanty of great single plains available
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Re: Dual Plane Center Divider

Post  rmcomprandy on March 22nd 2018, 6:21 pm

Doug Rahn wrote:Is there any significant advantage in cutting down the plenum center divider some?

From what I have experienced in many, MANY tests.  You will gain some horsepower and lose twice that amount in torque below peak torque.
So, it really depends upon what you most want to accomplish.

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Re: Dual Plane Center Divider

Post  TravisRice on March 22nd 2018, 6:38 pm

Not to hijack the thread but a divider question as well.

Performer RPM AIR GAP, mine had the spreadbore pattern, I used a 1 inch open square to spread bore adapter to run an 850 vac. secondary square bore carb. The AirGap has notched center divider, drops about 3/4". I was wondering if I would benefit from putting a groove vertically in the 1" spacer to add a removable center divider that basically recreated the original 3/4" drop instead of the current 1-3/4" . Any thoughts on the effects as it sits compared to extending the plenum to 3/4 below the carb mounting point? Will I notice a difference in part throttle , off idle or cruising speeds? Opinions?

532, 9.5:1 iron D3 cylinder heads, hydraulic roller 224-244/ 560-580ish lift . Recurved duraspark, 2wd pickup ZF5speed with 4.10's.

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Re: Dual Plane Center Divider

Post  rmcomprandy on March 22nd 2018, 10:12 pm

TravisRice wrote:Not to hijack the thread but a divider question as well.

Performer RPM AIR GAP,  mine had the spreadbore pattern, I used a 1 inch open square to spread bore adapter to run an 850 vac. secondary square bore carb. The AirGap has notched center divider,  drops about 3/4". I was wondering if I would benefit from putting a groove vertically in the 1" spacer  to add a removable center divider that basically recreated the original 3/4" drop instead of the current 1-3/4" . Any thoughts on the effects as it sits compared to extending the plenum to 3/4 below the carb mounting point? Will I notice a difference in part throttle , off idle or cruising speeds? Opinions?

532, 9.5:1 iron D3 cylinder heads, hydraulic roller 224-244/ 560-580ish lift . Recurved duraspark, 2wd pickup ZF5speed with 4.10's.

In short ... YES.  
The more separated you make it, the more torque you will notice, (below peak torque RPM), you will also experience about half that amount of loss in the maximum horsepower number.

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Re: Dual Plane Center Divider

Post  TravisRice on March 23rd 2018, 5:41 pm

Thanks. I never really understood the purpose, but the explanation and test results have me a better understanding to why. Been going to do that since I got it running. This evening might be as good as any as my twins have school friends over for a sleepover and no volleyball this weekend for my oldest.

Much appreciate the info.
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Re: Dual Plane Center Divider

Post  Doug Rahn on March 24th 2018, 6:28 pm

Thanks for the replies guys. Randy pretty much answer the question for me. I was installing a new QFT Marine carb on my boat engine and was wondering if it would be worth the time and effort while I had the carb off. I'll leave it as is.
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Re: Dual Plane Center Divider

Post  TravisRice on March 25th 2018, 2:24 pm

Thanks for asking the question Doug and Randy for chiming in. I was looking for an answer as well. Spent Friday evening making a divider extension that fit in my spacer. Trucks getting closer to being drivable. Taking it back to the painter next Saturday to get the bed put back on it and then he's going to button the rest of the body assembly up which includes the grille, hood and bumpers. Be nice seeing the thing as a whole again.

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If looking for drivability if I ran a 850 carb it have to be a 9380 Annular.

Post  ED468 on April 5th 2018, 10:39 pm

850 with dog leg booster have about the poorest signal down low as any carb, Very little venturi effect as well. With that combo be sure to run a vacuum advance distributor it will love it at cruise.

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Re: Dual Plane Center Divider

Post  427John on April 16th 2018, 6:19 pm

rmcomprandy wrote:
TravisRice wrote:Not to hijack the thread but a divider question as well.

Performer RPM AIR GAP,  mine had the spreadbore pattern, I used a 1 inch open square to spread bore adapter to run an 850 vac. secondary square bore carb. The AirGap has notched center divider,  drops about 3/4". I was wondering if I would benefit from putting a groove vertically in the 1" spacer  to add a removable center divider that basically recreated the original 3/4" drop instead of the current 1-3/4" . Any thoughts on the effects as it sits compared to extending the plenum to 3/4 below the carb mounting point? Will I notice a difference in part throttle , off idle or cruising speeds? Opinions?

532, 9.5:1 iron D3 cylinder heads, hydraulic roller 224-244/ 560-580ish lift . Recurved duraspark, 2wd pickup ZF5speed with 4.10's.

In short ... YES.  
The more separated you make it, the more torque you will notice, (below peak torque RPM), you will also experience about half that amount of loss in the maximum horsepower number.
So would a 4 hole spacer be advantageous here or do you want to try to emulate the carb mounting surface on the intake?(ie.2 oval holes,4 holes,or the swelled out sec. area like some intakes have)Also am I correct in assuming this philosophy would apply to smaller cu in. engines too?

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