The Air Gap manifold thread has a discussion on milling the divider on dual plane manifolds. The theory is it evens out A/F distribution. If that’s the case, why isn’t the manifold cast that way? I would assume since it’s not, there must be an application where the intact divider is needed.

I remember in high school someone bought a aftermarket manifold for their project car, then had a friend mill the divider. I remember thinking at the time how wrong it seemed, why did Edelbrock (or whoever made the part) spend so much time and effort to design and cast a manifold the way they did if it didn’t work? They have access to flow benches and far more test equipment than almost anyone, I assume they would know what they are doing.

 

Yes, that's logical. But dyno tests usually show better fuel distribution and higher power if the divider is milled or an open spacer is used between the carb and manifold.

I have a Performer manifold that Wilson Manifolds installed port fuel injection on. As part of that installation, they milled the divider into a 1"-deep "V" shape with a flat bottom about 3" long. I didn't ask for that. They just did it automatically.

For documented examples of power gain and effect on mixture, read some of the dyno test threads that JerryW is currently posting on this site.

 

Dyno tests are not a good representation of how an engine behaves on the street in daily use. A street driven car in the real world has requirements on part throttle flexibility. What works on the track doesn't necessarily translate to street manners while driving to the grocery store.

 

I've read that the divider in an intake manifold can cause problems for some EFI systems.

 

Back in the day a three barrel Holley would have required milling the divider down. Maybe someone noticed a gain after swapping a four barrel back on?

More likely some regular guy saw a serious racer milled the divder down and copied it, and here we are 50 years later...

 

The thing that people need to understand is that the benefits (or lack thereof) of milling the divider or using a spacer or whatever trick is currently in vogue are HIGHLY dependent on the engine details and how it is used. Anyone who claims that such and such a trick works every time on every application is wrong.

 

Thats kinda where I was going. Just cutting the divider based on the assumption that it’s an automatic benefit is gamble. It’s far easier to cut it out than to put it back in. And without some A-B testing, how would you know?

 

It is a good question. I saw a popular sbc intake with the divider cut as cast, similar to a rpm intake. The same argument was made, just use a spacer, which can also add power. But sometimes the spacer loses power. I wonder if the same is true with the divider or if is always a positive. If it is, then why doesn't Edelbrock do it, as cast?

 

I can tell you why I did it....when I was unhappy with the performance of my QJet SNIPER system, I switched back to an Edelbrock Performer intake. I knew I wanted to keep using the RAM air setup so a spacer was out of the question. Several of my tuner friends recommended that I cut down the divider and go back to the 4150 style SNIPER system. I called Wilson Manifolds and asked them two questions. 1. What are the ramifications if I cut down the carb mounting pad 1/2" and what would they recommend with a Holley SNIPER and the center divider? They told me their engineering data showed that cutting down the carb pad would be fine and actually accelerate the air going into the manifold and they recommended a 5/8" divider cut for the center divider. I followed their advice and my engine runs incredible now. This is with removing the OEM aluminum W-30 intake and QJet SNIPER (That had been professionally tuned!) and swapping back to the 4150 style SNIPER, making the intake modifications, and then running a dedicated fuel return line to the throttle body rather than running a recirc fuel pump which recircs fuel in the tank. There was a world of difference for these changes.

Here is a link to one of my posts showing the changes that I made and some pics. https://classicoldsmobile.com/forums...sniper-162811/