Modifying a dual plane??

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4spdragtop

4spdragtop

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I picked up an LD4B from Karl for Dads 67 cuda :blob: The plenum has not been modified at all. Im curious as to whether I should modify and if so, how "deep" do I cut it down?
What are the pros/cons of doing this mod?
Dad n I redid the top end, click the link at the bottom for the cam specs. Car has
1405 Eddy carb
904 trans
3:23 sure grip

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=665&sb=2

Thanks
Steve
 
Without the entire specifications on your motor.

I would leave it alone, the intake just works, I have one on my old truck.
Excellent street intake on a 318 good torque and road manners.

I run a 625 street demon on mine, but your 1406 if it is fresh should also be snappy.
 
You can cut the center down leaving about a 1/4" inch and round it off. That was the old modification for the LD and other manifolds in the direct connection books back in the day. Not sure you would feel anything doing this.
 
sireland67 said:
Without the entire specifications on your motor.

I would leave it alone, the intake just works, I have one on my old truck.
Excellent street intake on a 318 good torque and road manners.

I run a 625 street demon on mine, but your 1406 if it is fresh should also be snappy.
Click to expand...

Sorry should have mentioned engine is stock.other than the 270s cam lifters springs dbl timing chain and gears. Piston are low compression. Im going to attempt to port match heads with the intake in the spring.

Thanks
 
EL5DEMON340 said:
You can cut the center down leaving about a 1/4" inch and round it off. That was the old modification for the LD and other manifolds in the direct connection books back in the day. Not sure you would feel anything doing this.
Click to expand...

What was the.purpose of cutting down the divider?

Thanks
 
Cutting down the divider is essentially turning it into a single-plane; might help you if you are looking for an edge at the races and can't swap to a proper manifold but on the street it won't do anything for you. Might even take some torque off the bottom end.

EDIT: If you really want it would be a better idea to experiment with an open spacer under the carb that will have basically the same effect
 
MOPEkidD-3 said:
Cutting down the divider is essentially turning it into a single-plane; might help you if you are looking for an edge at the races and can't swap to a proper manifold but on the street it won't do anything for you. Might even take some torque off the bottom end.

EDIT: If you really want it would be a better idea to experiment with an open spacer under the carb that will have basically the same effect
Click to expand...

Indeed this is true.I run a carb spacer on my RPM.I was told by a pro geek that single plane will give you more at the top and..
 
I would not touch the divider. Supposed to give you an extra 500 rpm and a few horses at the top end with a 340. May be an old Super Stock mod. That manifold is very good as is. If you are gasket matching do not match the bottom ports of the heads.
 
Many of the manifolds had a "notch" on the secondary side that allowed for the 3 BBl carbs to function. The lowering of the divider was for a little more top end. You could just add a 1" open spacer for a similar if not better effect.
 
Leave it alone,, is a fine street manifold as it is,, and removing divider was a top-end racing mod, losing some bottom end,,

For a stock street car,, is one of the best.. port matching would be more beneficial..

hope it helps
 
I actually went the other way with my M1 dual plane. I have a 1/2 inch wood spacer with a divider and it came with 2 open carb base gaskets. I cut 2 new gaskets that have the same center divider as the spacer. And I modded the carb bottom too. I'm using a Edelbrock carb and it has a large open hole under the air cleaner rod that allows air to move back and forth between the primaries and the secondaries. I filled that hole and also the vacuum port at the back by the secondaries. The idea is to stop crossover from one port to another.
The result is I have 2 inches more vacuum at idle and a crisper throttle response.
 
I have a buddy that races v mods and they build their own engines. He says just adding a one inch spacer nearly always added 15 hp on the dyno. I am building my 440 for my Ramcharger that will be street driven. He told me to make sure the cam and intake matched power ranges and to make sure I went dual plane so I would have good streetable power. I had my eye on a single plane and he said if I was racing it would be okay, but I would lose some torque but gain top end speed. Keep the divider in place.
 
bobscuda67 said:
I actually went the other way with my M1 dual plane. I have a 1/2 inch wood spacer with a divider and it came with 2 open carb base gaskets. I cut 2 new gaskets that have the same center divider as the spacer. And I modded the carb bottom too. I'm using a Edelbrock carb and it has a large open hole under the air cleaner rod that allows air to move back and forth between the primaries and the secondaries. I filled that hole and also the vacuum port at the back by the secondaries. The idea is to stop crossover from one port to another. The result is I have 2 inches more vacuum at idle and a crisper throttle response.
Click to expand...

I'm running a Carter currently I want to try this... I'm sure you picked up a little MPG too
 
MOPEkidD-3 said:
I'm running a Carter currently I want to try this... I'm sure you picked up a little MPG too
Click to expand...

IDK about the fuel mileage but it did make a difference in the low end. Plus since I used a fit piece of wood and I covered it with epoxy, it can be totally reversed.
If your interested I can post a pic of the bottom of my carb for you.
 
bobscuda67 said:
If your interested I can post a pic of the bottom of my carb for you.
Click to expand...

I know I'm interested! I have manual brakes now but if I ever wanna go power I'm gonna have to up my vaccuum somehow! I'm only pullin about 5-6 pounds at idle!
 
Some very good info posted. Thanks, for now well in the spring Im gonna leave as is and try it. Worst case is I have to buy another set of intake gaskets to do the mod. I have a 2" spacer but it wont work in keeping the stock look under the hood.
Its for sale if anyone is interested.
 
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