Hi everyone, I am curious about a stock tbi intake that I am putting on my 305. There are indentions in the top of 5 of the ports just before they enter the heads. I was wondering if they could affect distribution? Also are all the stock 2 barrel tbi intakes the same on different size engines or are some better than others? Thanks.

 

I have heard--but not verified--that the TBI intake manifold is poor from a mixture-distribution perspective.

First Guess: Several part numbers for mostly-similar manifolds.

 

From what I have seen in my research, in general it appears that most all dual plane intakes are pretty bad when it comes to even fuel distribution (even the aftermarket ones). In one test, wide band AFR was taken from each cylinder and the variance was 2 full points. Meaning one cylinder could be running on 12.5 AFR, and another could be at 14.5 AFR! Sorry I do not have a citation for this. I saw the thread on another forum quite a while ago, but it seemed like reliable information with real data to back it up.

Single plane is much better, and obviously port injection is quite good at even distribution as well.

I wouldn't worry about a little indentation on one of the TBI intake ports, because the AFR is going to be all over the place from cylinder to cylinder anyway.

 

The reason I thought it might be significant was that they are about 1/2 inch square and about 1/8 inch deep on 5 of the ports. Thanks.

 

They just help with air/fuel mixture distribution on a stock setup. Probably there to cause turbulence in some ports with slower flow.

On GM trucks/cars there are about 5 different factor TBI intakes.

The Fullsize truck/van manifolds tend to have a TBI mounting base that is 3/4" taller than a car unit. If you take a L03 F-car manifold and lay it next to a truck/van manifold the runners of the truck intake look slightly raised and the plenum taller. That being said I do not believe it benifits performance to a noticeable degree.