MagRed_04

What does the "Heat Riser" do? And What is a factory '85 head combustion chamber size? :confused:

vader86

76cc for our heads

MagRed_04

Anyone know what the "Heat Riser" is? Is this the same as an internal EGR system?

nobodyunknown

If your looking at your heads ,you see 4 intake openings.then half way between the intake openings right in the middle there is another opening or passage.It allows exhaust air to pass under the intake & warm it for cold weather driveability.
When you buy intake gaskets you might get a small metal plug that is designed to block that opening.

MagRed_04

Is that different than the EGR system? or the same thing? :skep:

Bill Reid

I believe on our 85's the EGR valve worked off of the exhaust gasses passing underneath it... allowing exhaust gas to recirculate back into the intake in most conditions for emissions reasons.

You'll notice on the 86-91 cars the EGR valve was fed off of the #8 exhaust tube. I think this was because the aluminum heads did not have the center heat hiser. I'm pretty sure of this... but I've been proven wrong before:)

FYI, another little tidbit of 85 information... I think its intake manifold was a 1 year only run (for corvette) ... not only did it not have provisions to accept external EGR gasses it also did not have rear cooling crossover. You'll also notice a small cooling line teeing off of one of the heatercore coolant lines tapping into the back coolant crossover on the intake on the newer years as well.

What confuses me a little is that the 86 iron head motors (early coupes only)had external EGR... as far as I knew they still used the same iron head as 85 but probably blocked off the heat risers because the aluminum heads weren't quite ready for production yet. Keep in mind I'm only speculating here... food for thought:)