Bee Jay

If it ain't broke, fix it. Earlier this year while I was looking for all of my lost low end torque and trying to figure out why I was getting terrible vacuum readings, a few of you suggested that eliminating the gap in the plenum divider would add a ton of torque and 100s of inches of vacuum. The problem was at the time was the timing gear being off a tooth. Easy fix. Vacuum and compression went up. But, my friend Gill and I decided to test the manifold gap theory. He built an aluminum gap filler and drilled and tapped screw holes and mounted and glued it in. I'm letting the epoxy and locktite dry overnight and will start and drive the car tomorow and see if it made a difference.
Bee Jay

Birdman

Hmmm...kind of makes me glad that I went with this instead:

bozzman3

Wow,You are brave!If just one of those screws comes loose your motor is toast!!!!!!!!

'75

Seems like the carb would have to be off for those screws to come out, looks safe to me. Nice job BJ, looking forward to the results.

STODD

One of the chevy magazines (Super Chevy or Chevy HP)tested about 30 s/b manifolds last year, the rpm airgap is an easy winner, even besting super victors and other high end single planes up to about 6500, on a mild and a built motor.
I already head the Dart airgap, which I thought was the same until I read this article, you have the right manifold, right out of the box!!! Wish I had one. Good luck with the fix.

fugawi

very interesting. waiting for results as i have an air gap also..

Bee Jay

Yea, but my divider is easily removeable. When I build my big small block and have it dynoed, I'll know exactly what this notch in the plenum divider does.
Bee Jay

Bee Jay

Thanks '75. Your right. No way for the screws to come out with the carb mounted. Heck, with the epoxy and locktite, it's going to be a biotch to get it out even then. I get bored and curious sometimes. I should have vacuumed the downstairs carpet like the wife wanted. My Vette is a hobby and a test tube. I get to drive it today and see if my butt dyno feels anything. My air fuel ratio and vacuum gauge might show something, but it's my butt that has to be happy.
Bee Jay

Avette4me

Corey_68

If I were you I would use aircraft wire/bolt fasteners like this.

Avette4me

That won't allow for a flush surface at the top, will it?

pauldana

results...

o... hey BeeJay!!!

Corey_68

it will not, but the alternative is grenading the engine.


Personally I leave the divider out or purchase a new intake, both are cheaper than the alternative.

Taijutsu

BJ: Any chance of testing a carb spacer? I don't have any dyno time planned any time soon. A spacer is on my list of things I want to try.
Your plenum mod was also on the list! LOL
Thanks for keeping us posted.

R

Avette4me

To me, those little saftey wires would be dangerous after they baked for a while. Besides, he said that the carb won't allow the fasteners to come out.

I'll be interested in seeing how the butt dyno reads.

terry82

why is that gap there to begin wth ?

MotorHead

What you have done is defeating the purpose of the cut down divider and effectively changed what makes the Air Gap such a good manifold, one of the best out there.

The cut down divider is to allow this dual plane manifold high RPM performance while still allowing low end power too.

I doubt you will notice any difference unless you do a back to back chassis dyno session with and without your spacer insert. What you will find is approximately the same low end torque but you will lose some HP around 6000RPM and above with the insert in the manifold.

I did a back to back test between the Air Gap (dual plane ) and a Vic Jr( single plane ) and found the low end torque and HP to be pretty much the same until around 6000RPM where the Vic jr pulled a couple more HP out of the motor.

I would have used the RPM Air Gap ( I did for a year or so ) but I switched to Vic Jr when I found out contrary to popular belief the single plane didn't "lose" any TQ compared to the dual plane Air Gap and I like the looks of the Vic Jr better. So it really came down which manifold I liked the looks of better because this motor was only really capable of about 6000RPM so the performance of one or the other didn't really matter.

Now my new 427ci small block is capable of ~8000RPM and the Vic Jr was the only manifold I would put on

So these are the results of 2 specific manifolds and may or may not hold true for any other dual or single plane manifolds.

Taijutsu

MH: Would the increased displacement of your engine be a reason the AG and the Vic jr are so close? All those cubes need extra cfm, the Vic jr does flow more. Most tests on 350 SB show a Vic jr is a little much for the smaller milder SB. A 427 @ 8K will need mucho cfm! LOL

R

Corey_68

Those wire/nuts are derived from military aircraft applications FWIW, they hold up to stress fine.

Lets us know the results

Bee Jay

Corey, the bolts are almost an inch long. No way for them to come out with the carb in place.
Motorhead, my engine is only 350 cubic inches. It wants to grow up and be just like yours some day. I've read in several places that cutting down the center divider adds high rpm horsepower but lessens low end torque somewhat. I just wanted to try it and see. Easily removeable, so no harm, no foul. I just got back from church. The wife is putting dinner on. Then I'll get out of my 1st Sunday monkey suit and put on my speed racer suit. Details at 11.
Bee Jay