C-4 Production Question

[John D.]

The 1984-1986 NCRS TIG states the 1986 heads were cast iron until mid production. What is considered mid production based on the VIN #?? How can I calculate the build date on an 86 based on VIN?? The last 5 #s are 26773, so would this be a cast iron or aluminum head car? Build date?

I have heard the CI heads were better, any thoughts?

Thanks, John.

[Joe L.]

Re: C-4 Production Question

John-----

As I recall, all 1986 convertibles had the aluminum head L-98s. I'm not 100% certain of that, but that recollection seems "firmly implanted" in my "memory banks". I seem to remember that when I first heard about this (back in 1986), I was surprised that GM would assign the engines to assembly this way. It seems like it would be more trouble than it's worth.

However, by the serial number, I see that your car is a coupe. For coupes, about the last 25 or 30% of production were aluminum head variety engines. Your car easily falls within this range, as it was one of the last 1,000, or so, produced. I feel very confident that yours would be an aluminum head engine. If it still has the original block, you can verify this by the engine suffix code as aluminum head and cast iron head engines used different suffix codes.

I don't think that there's much difference in performance between the aluminum and cast iron head engines. Aluminum, of course, saves some weight.

[Don G.]

Re: C-4 Production Question

Joe is correct.

The aluminum heads were used on all convertibles and all coupes built after convertible production started. Although I don't have an exact number, approximately the last 5000 coupes had aluminum heads. The last coupe VIN number for 1986 was 27794

Horsepower ratings increased from 230 to 235 with the aluminum heads. Another quick check to verify an aluminum head is the valve cover. It has mounting screws in the middle of the cover while the iron head covers are on the outboard edge.