Completely removing the divider from a dual plane, empirical data?
 

I have an original HO intake at SD performance getting going through his full CNC program, but the intake had already "surffered" from the previous owner "tuning experimentations".

The divider has been completely removed from the intake and was probably why I got a better deal on this vintage HO piece many years ago. I was always told, and I always told people that only idiots did that , especially to a rare intake like that one.

But I as get older I try to be a little more open minded :rolleyes:

Dave will run it through the programm anyway, and for whatever reason I didnt tell him to weld a new dividier in. Probably because I thought I'd weld it myself trying to save 5$ :p

I was just curious to hear from people who tried similar experiences on Pontiac engines, maybe engine builders and induction gurus like Cliff during his Iron Qjet intake exploration.

Some aftermarket dual plane intakes were sold without a divider brand new, one that comes to mind is the not too shabby Weiand Stealth 8019 for BBC with ovals...

I was just curious , Im almost tempter to run it as is, or send it to Cliff is he wants to compare with his intakes.

These are pictures of the intake when I bought it , NOT after Dave's CNC cut...
and one from the Weiand Stealth 8019.

what you guys think...

I'd create something like this and try it before going to the trouble of welding something in permanently. You could have a nice before/after comparison on the dyno.

I think its a great idea, but since Im running a Qjet this little device wouldnt work, that said my original idea was to machine a continuous groove on the 3 faces to slide a 1/8 divider plate in and to hold it while I tig weld it in place.

Before welding one, if I had access to a cheap dyno I would surely play with different plates shapes, height.

Peter

I'd fix it. 99% of the time that kills power and I'm still looking for the 1% that it doesn't.

If there's no ledge between upper and lower planes, I'd expect the upper plane to run lean, and the lower plane to run pig-rich, as liquid fuel would "waterfall" to the lower plane.

I suppose even a 3/8" to 1/2" remnant of that divider at the bottom would help immensely.

GM sold intakes for BBC that had the divider almost completely removed. L88, I think.

If you look at the picture of the Weiand I posted , its indeed completely removed..

Peter

FWIW the NASCAR 380 HP 409 ran an intake like that.

I guess ill have to paint a #3 on my doors and please call me Junior Johnson :p

That's funny

As mentioned gm did this on oem intakes for the L88 and ZL1 and I've seen nascar intakes done this way just like Skip mentioned.
Been a long time since I've seen a Pontiac nascar intake and can't remember how they were done.

But in a street application I can't imagine it would be beneficial. I have no experience doing this on a Pontiac but if Paul says it hurts HP I'd take his word for it. Probably won't be spinning it high enough in a street application.

Some guys in the FAST class running BBC's are still modifying stock intakes this way from what I've seen but they are mainly worried about high rpm power.

I'd get a qjet open spacer and fab something up , might take a while to get the contour of the divider just right. This could be one of those times when a cheapie contour gage is actually useful.

Did it stay in the back, or Did it win?

The cut divider should have zero impact at idle, and idle transition, and high RPM.

Perhaps some effect (bad or good) in off-idle romp, and 2000-3900 rpm dyno compare.

Interesting test would be highway passing gear response.

https://www.youtube.com/watch?v=_tg8MEdOdkM
Tribute car to the 409 that won on a Super Speedway with the 380 HP motor with cut down divider. Although this car has an alternator vs generator and a dual master cylinder and power brakes.

It's essentially a bastardized single-plane. GM did it on the Corvette engine because they weren't interested in tooling up for a single-plane manifold. Like most single-planes, it'll have low-velocity airflow at low speed, reducing signal at the carb.

Cutting the divider so the work is done with best practices, it might make more higher-rpm power especially decades ago when carb CFM tended to be lower than what's available today.

But with no ledge holding puddled fuel in the upper plane, air/fuel ratios are completely out-the-window. There's a reason that manifold was removed from the engine and sat on a shelf.

This is a stock vs "Vanke" modified Hemi intake

Interesting. Notice the 7-5 isolation curve. I think it would be same effect for 2-1 isolation.

My testing shows that the divider needs to be there, full height with at most about half a 50 cent piece removed between the secondaries. I've "notched" and made drop in dividers from aluminum flat bar more times than I can count when over zealous folks followed POOR advice on the Forums and ground the divider way down or completely out of dual plane intakes.

We actually had a customer who ran FAST dyno test than deal and it KILLLED mid-range power but made 1-2 more HP WAY up on top end. Sadly in actual use in also induced a "stumble" going quickly to full throttle that would NOT tune out. When I made a drop in divider for the intake ALL running issues went away and the car went on to run well into the 10's even though it used the "crappy" 4X heads, log exhaust manifolds and EGR iron intake.

A good move instead of notching out your divider or cutting it down is to simply use a 1/4" thick gasket either fully open or even better notched out between the secondaries.........

That's exactly how I test if this mod is even worth doing on any engine first. It's simple, it's fast, can be done on the dyno or in the pits in about a minute flat, it's easily reversible if it doesn't work, and it only costs the price of a gasket, or a spacer. ;)

Jim Hand did quite a bit of experimenting with his intake testing. His results were the same as Cliffs.

Most of the street/performance driving that our Pontiacs see, I'd think could benefit from the nearly completely intact divider.

I will welding a divider back in that intake when Dave will be done with it and blend it in the plenum. I was just curious to see what you guys thought.

I am going to be running my 3/4" nitrous plate on that intake so the divider wont seal against the Qjet. There will be a gap over and under the spray bars.

Would it still be worth it to cut a notch in the divider between the secondaries ?

Peter

I'd leave the divider in, and see how it does. You can always put the notch in later, if needed. The power gain the notch gives would be very small.