Anyone know what this flange is for by distributor hole . I compared it to my 85 L98 base and it doesn't have this flange . Haven't checked my car yet since I discovered this difference thanks

I believe that flange to the right of the dizzy hole is an external egr port. Corvettes used this since the ports weren't cast into the heads.

EGR port for a corvette, they did not have a heat cross overs in the heads.

Really that is strange. I have a 85 L98 from a Vette and the stock base doesn't have the flange . I wonder if the 86 up had this and not the 85 because it has cast iron heads . Thanks for the reply . The edelbrock base has the casting number 3860 on bottom .

85 L98 Vette base

The likely change was from iron heads with the heat crossover/egr passage from head to intake, changing to aluminum heads that did not has the exhaust-to-intake passage, and required an external source for EGR.

Blow some air through the rear passage, and it will come out at the EGR pad at the center of the manifold.

Yes, i have a 86 vet base used on the aluminum heads and it has the flange. Its most def because of the egr port placement.
The aftermarket makes parts that have to fit many different applications to make them cost effective to produce.

Ya that makes sense. So what other heads could i use like are they a vortec head basically uses rear egr ?

No, you cannot use these with vortec heads. (Not without A LOT of custom welding and machining.) The mounting points are different, and the manifold ports will not cover the vortec head ports.

The center bolt holes look to be slotted. This means they are compatible with both:

• older, perimeter valve cover bolt heads... The center intake bolts are at the same angle as the front and rear bolts.
• the later model, center-bolt valve cover heads, where the intake center bolts are more vertical than the front and rear.