Günther-C3

Hi!
I´m in process to exchange the stock intake mainfold to a LS6 intake (and AED carb) of my 489ci stroker BigBlock. I read several times that milling down the divider would gain some HP and TQ. Would you recommend me to mill it down or not? Max. rpm is about 5500-6000.
Thank you, Günther

cv67

Id leave it be and get a bigger intake if you want more...youll get a better signal to the carb not cutting it out
It never helped any of mine but did notice my idle/tip in quality suffered some.

69427

I've got a spare intake that I've milled down the divider to try out that setup next summer. I corresponded with several guys on the Chevelle Forum about this topic. There's quite a few big block guys on that forum who are very happy with the results when they did that.

PAmotorman

you will need to stagger jet the carb and have boosters with distribution tabs in the correct location to get max performance.

REELAV8R

ronarndt

The Weiand Stealth intake I have on my 454 has the divider milled down about 3/8 inch. Weiand claims it is to give better performance without going to a single plane intake, where the low rpm would suffer.

Jebbysan

Any dual plane intake benefits in flow from milling the divider out.......the ZL-1/L-88's were almost removed from the casting back then......for racing they were milled and the corresponding plenum area milled out larger.......the LT-2 454 test car was milled out and a dominator plate welded on it.
A 489 needs as much flow as it can get so I say mill it.......any 489 is going to make 600 ft/lbs. torque easily, and the swept volume far out ways the LS-6 manifolds ability to move air.
VortecPro made amazing power with this manifold but unsure if it was milled.
I say do it......with an engine that large.....the intake is a cork.
The only reason dual planes exist is for carb signal....they signal a carb better below 3000 rpm than a open plenum. Of course milling this negates the whole idea.......
A dual plane make more average power apples to apples strictly due to carb signal....that's it....that is how it works......it tricks the engine into think it is two four cylinders, it is actually ingenious how it works......
If you can make an 850HP and a Super Victor signal on a stock L-48.....you will make about the same average power and never know it was on there.......

Jebby

pauldana

Jebbysan

I also want to add that putting one of those HVH "Super Sucker" carb spacers on a Dual Plane intake is a waste of $200. But on an open plenum intake....it can help signal the carb much better at certain points in the rev range.......
Also...if you stare at a dual plane intake and pay attention to the runner layout....you can roll through the Chevy firing order in your head, point to the runners and notice that they are orientated LOW/HIGH.....the higher runners come right after the lower runners and skip back and forth......this increases the amount of available vacuum at the booster by having the booster pulled by a predetermine set rather than from any of the eight pulling from one plenum.
Think of it like this:
L H L H L H L H
1 8 4 3 6 5 7 2
This splits the pulses in half.......

Jebby

TimAT

I sure messed that up-- my firing order is 1 8 7 3 6 5 4 2. That poor old Weiand manifold is probably confused as heck.....

Jebbysan

larrywalk

Whether you have a 4-7 swap or not, the dual-plane manifold flow sequence is still L-H-L-H-L-H-L-H.

69427

I'm not seeing the difference between the original firing order (with the 5-7 issue you mention), and having a revised firing order resulting in cylinders 4 & 2 pulling sequentially out of the same corner.

Jebbysan

Hey......I hear ya....but I didn't come up with it, NASCAR did......some 12 years ago......I never saw any benefit to it, and if you sell it to somebody and they don't know, expect about 20 phone calls and conspiracy theory......I never run them.
They are in the Comp catalog if you want to check it out though.........

Jebby

Jebbysan

Yes...thanks for pointing that out.....but the lobe swap was intended for 1x4 single plane intakes......
I don't think it makes a s&%t bit of difference, but as it was explained to me by Gordon Halloway at Comp......the vacuum pulses coming from that corner are one after the other and can create distribution problems at high RPM (6000+)....but to me it is rob Peter to pay Paul.....so a 4-7 as designed would have zero effect on a dual plane if I could tell you it worked at all.

Jebby

gg521

To get back to the original question, here is a video that discusses the subject.

Günther-C3

Are there any drawings out there how much to mill out?

PAmotorman

I believe the GM sold chevy power manuals have the specs

69427

As PAmotorman mentioned, the Chevy Power Catalog recommends leaving a quarter inch ridge between the plenum halves.

7t9l82

That's exactly what we used to do , leave a 1/4" lip.back when we didn't have near as many intake choices nearly every one did it.