I have a 92 RS 305 TBI (all stock), & I just removed the stock intake manifold b/c it had a tiny crack in the manifold at the front & coolant very slowly seeped out. The leak was so slow, that it only leaked about a 1/2 gallon of coolant every year (it only leaked in the summer months).

The car has always ran great & the manifold has been cracked for about 3 years, & I could've driven it for another 3 years like this, but I decided to replace the manifold b/c I had the time.

So after I removed the intake, I noticed that the rear head passage on each head had metal caps blocking them, & the new gaskets also have those passages blocked as well, but they are covered by gasket material.

Are those coolant passages that are blocked? Does anyone know what those passages are for & why they are blocked?

I bought the blue felpro gaskets.

 

Yes they're coolant passages.

 

When you buy new gaskets they will be the same way, the two rear passages will be blocked off.

 

if you buy felpro gaskets there will be holes in the gasket material for those rear passages. i purchased gm intake gaskets and the rear orfice was metal. they seem to work a lot better. here is the part number

12525810

 

If these are coolant passages that are blocked off by the intake gaskets, do we need to remove the block off plates so that more coolant can flow through the intake?

I'm just not understanding why they are blocked off.

Does anyone know why the passages are blocked?

 

So do we leave these passages blocked off or not?

 

It forces coolant to flow from the front to back to warm the entire intake for good fuel atomization.
If your putting a stock intake back on, put stock gaskets on.

 

no do not block them off if you want good fuel mileage. and no it wont hurt performance as the tbi is limited anyway.

 

What does fuel mileage have to do w/ those rear ports? GM blocked them off for a reason, getting bad mpg aint it.

 

why are people saying they blocked them off. if you order the gaskets there is an orfice not a block off. you can get the gaskets that block them off but why. and it heats the intake a little more but i doubt a whole lot of mileage comes from it. prolly more of an air pocket thing to allow the coolant to run from the heads in front and back.

 

The rear coolant ports that are blocked may have a small hole in the center to allow air to escape. Thats the way they came from the factory.
Look at the gaskets, they say "front" on them. I don't think he'd notice either way (w/ or w/out open ports), its more of a cold weather thing, like those tpi coolant hose to the throttle body.

 

i believe if the orfices were put in the front it would effect the coolant sensor. heck maybe the holes like they are is one of the reasons they are hard to bleed. i know when i went to carb and had them blocked off i didnt have to bleed the cooling system. since i went back i did have to bleed it out.