open or divided plenum
Thread Starter
Racer
Joined: Aug 2009
Posts: 307
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From: dallas texas
open or divided plenum
i'm in the process of installing a new big block in my '66. 496ci, 600hp, 600tq. i don't plan on racing it but i do enjoy being nailed to my seat! i'm going back with the 427/425 aluminum intake and a holley 850cfm. should i go to the open plenum l-88 intake or stay with the stock divided intake. thanks, tjs
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A divided or 180 degree design plenum is the best for the street. Higher manifold vacuum and better throttle response. As the plenum under the carb.gets larger the better it is for higher RPM. Not so good for the street.
I don't ever recall seeing an undivided plenum on a production engine.
Joe
I don't ever recall seeing an undivided plenum on a production engine.
Joe
Thread Starter
Racer
Joined: Aug 2009
Posts: 307
Likes: 1
From: dallas texas
thanks for the info joe. i was leaning toward the divided intake but i wanted some more input. it will probably cost 20hp on the top end but should help it's street manners. i call it the "hemislayer"! tjs
Burning Brakes
Joined: Jul 2009
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From: Sarasota,FL & NW Indiana
Open
i'm in the process of installing a new big block in my '66. 496ci, 600hp, 600tq. i don't plan on racing it but i do enjoy being nailed to my seat! i'm going back with the 427/425 aluminum intake and a holley 850cfm. should i go to the open plenum l-88 intake or stay with the stock divided intake. thanks, tjs
made with a 4 3/8" stroke. You should have more than enough low end
torque.
IMHOJim
Drifting
Joined: Dec 2005
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From: Valrico Florida
I believe the GMPP ZZ502 has the divider cut down about a half inch. You can even the intake pulses by changing the cam so that the 4 and 7 cylinders are swapped in the firing order.
Last edited by Vogie; Aug 26, 2010 at 12:26 PM.
Thread Starter
Racer
Joined: Aug 2009
Posts: 307
Likes: 1
From: dallas texas
hey jim, thanks for the input. it does have the 4 3/8 stroke. i have a stock 3885069 intake with the divided plenum that i'm going to start out with. new 3885069 open plenum intakes are readily available on ebay and i'll probably get one later just to see the performance gain. this is a great engine combo with afr heads and a solid roller. a similar motor made 662hp and 680tq on the dyno with an open plenum edelbrock.
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Le Mans Master
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From: Santa Ana CA
You could always try it before you divide it.
Simply put a 1/2" open spacer between the carb and manifold and this will almost simulate cutting out the divider. I say almost, because you do gain a bit of plenum volume as well as a gentler radius that you will not get by cutting down the divider.
If hood clearance allows, close the hood and try it out. If clearance doesn't allow, try it with and without the spacer on the dyno with the hood up, or remove the hood, or even just the air cleaner element and top (but be sure the base is in place), for a test drive.
Simply put a 1/2" open spacer between the carb and manifold and this will almost simulate cutting out the divider. I say almost, because you do gain a bit of plenum volume as well as a gentler radius that you will not get by cutting down the divider.
If hood clearance allows, close the hood and try it out. If clearance doesn't allow, try it with and without the spacer on the dyno with the hood up, or remove the hood, or even just the air cleaner element and top (but be sure the base is in place), for a test drive.
Thread Starter
Racer
Joined: Aug 2009
Posts: 307
Likes: 1
From: dallas texas
tod thanks for the input. i was thinking about trying a spacer and using a low profile breather if my hood clearance will allow it or possibly fabricating a breather that pulls air in from the hood grills similar to the l-88 setup. tjs
