dual plane manifold plenum notch

[Pete Munroe]

All,

About to install the Stealth dual plane intake manifold on my 347" engine rebuild.

Considering modifying the dual plane by adding a notch to the plenum wall like Performer RPM Air-Gap. About 4 inches long, ~ 1/2 inch deep.

Supposedly this will let the manifold behave a little more like a single plane at high RPM, but still retain a good amount of torque at lower RPM.

Not sure with my build mild build it is worth the trouble.

new CompCams 284RF retro-roller...224/224, 0.533/0.533, straight up
with 1.7 rockers.
TrickFlow heads, 2.02/1.90 with 170 cc runners.
headers 1-1/2 inch ID
compression static 10.7/1
carb currently a 750DP
rear end 3:55 with Tremec 3:27 first

Old cam had less intake duration @117 more exhaust @226. Would pull pretty well to 6500 in fourth.

Anything to be gained by notching the intake manifold plenum at this performance level? Goal is to shift the power band up a little.


The Edelbrock Air-Gap with plenum notch is now quite popular, and actual hp/torque numbers notched vs normal separated plenum would be interesting.
(odd that the Edelbrock add copy mentions the obvious air-gap and I think totally neglects to mention the plenum notch)

Pete

[vatdevil]

May or may not improve power as every combo is different. I would try a carb spacer first.

[cobra 53]

Search on You Tube under: manifold test on Westtech

Rico

[Pete Munroe]

Vat and Rico,

The WESTECH video's are good, covers the topic of notched plenum vs stock.

Their test mule is quite a lot stronger engine than my configuration but still pretty useful information.

Don't think I have room to add a 1 inch spacer in the ERA, but apparently adding the spacer just about gives the same results as the plenum notch.

Westech has a series of videos that are well made...except for a camera man apparently compulsively moving the camera back and forth.

Thanks, Pete

[DAVID GAGNARD]

here's my uneducated theory:

On the dual plane with the plenum divider,basically one side of the carb feeds 4 cylinders and the other side feeds the other 4 cylinders.....when you add in the notched plenum divider,it lets thing "equalize" to some degree, allowing all 8 cylinders to pull fuel from both sides of the carb instead of 4 cylinders pulling from 1/2 the carb.......

according to the video results,the one inch spacer basically does the same thing........adding the spacer on a notched plenum divider is the best of both worlds,but if you don't have room for the spacer the notched divider will help....

on a side note,you can get an 3/8's inch thick open gasket to go under the carb if you don't have room for the one inch spacer and that should help out some.......

some years ago I did notch a standard RPM dual plane manifold, the car did idle and run smoother at low rpms and I'm sure it made more power thru the rpm range, but one would only be able to tell on a dyno......

David

[Pete Munroe]

David, et al,

Anyone with the Edelbrock Air-Gap...would you measure the depth of the cut in the plenum...? looks like 3/4" or so...may as well try to duplicate the Edelbrock.

Have masked off the manifold .passages and will be using a large bur and 3/8th's drill to grind the aluminum...I am sure the aluminum is harder than I think.

Seem to have misplaced my Bridgeport Mill...

Pete

[DAVID GAGNARD]

Originally Posted by Pete Munroe

David, et al,

Anyone with the Edelbrock Air-Gap...would you measure the depth of the cut in the plenum...? looks like 3/4" or so...may as well try to duplicate the Edelbrock.

Have masked off the manifold .passages and will be using a large bur and 3/8th's drill to grind the aluminum...I am sure the aluminum is harder than I think.

Seem to have misplaced my Bridgeport Mill...

Pete

Pete:

It is closer to 1/2 of an inch,at least that is what I remember,I would think anything between 1/2 and 3/4 of an ich would be fine and the aluminum is actually softer than you think.......with a 3/8 th's drill and good burr, it will cut like butter, not hard to do at all......

David

[vector1]

put an open spacer on top for a test drive, would give you a good indication of the result.