186 heads for the 302

[usa1ti]

I recently picked up a very nice numbers matching 1969 Z28 DZ car. Have been really pleased with prob 90% of the original parts there with correct date codes. First week May 69 car. The only disappointment was the motor must have had a problem around 1975. the heads were replaced with a set of over the counter straight plug 492s, F 29 5 dated. I can fix that with a set of A,B,C or D 186s. The question I have is do the original 186s have screw in studs and guide plates from the factory in 69? and I assume they were all 2.02 valve heads. Thanks for everyones help. You guys are a wealth of knowledge.   

[69Z28-RS]

186 head castings were built originally with either 1.94" or 2.02" intake valves.   186 heads for the '69 z28 302 did NOT have screw in valve studs OR the guide plates.   Those came along in the 1970 year cars...

PS.  If you are looking for 186 heads some consider the 1.94" valve heads to be preferable to the 2.02" factory heads because you have more meat to cut out for the 2.02" valves when you rebuild them for 2.02.  Note that there are additional machining within the combustion chamber that should be done to make them 'match' the factory 2.02" heads.   

[70z28lt1]

The "additional machining" referred to is an unshroud cut around the larger 2.02 intake valve.

On this topic, can anyone confirm that the Flint engine plant was the only one with the tooling to do this cut and that is why all SHP small blocks came from Flint?  Seems like I read that somewhere in the past.

[jdv69z]

Correct, the tooling to unshroud the valves on the 2.02 heads was only located at Flint, so no 302's were manufactured at Tonawanda. this info was from John Z. There are heads out there claiming to be 2.02 heads without the correct machining. Only larger valve installed. Caveat Emptor.

[69Z28-RS]

From your photo of an unshrouded 202 vs a 1.94 cut to a 2.02 without unshrouding, it would appear that a 2.02 head combustion chamber would be higher volume than the 64cc of the 1.94 valve head???  is that true or how much difference in combustion chamber volume?

[jdv69z]

Not my photo. Do Not remember where I got it. Would seem that you would have to be right about the cc volume. I have also read some where that the stock 194 heads actually flow better that the ones with larger valves added, but without the appropriate unshrouding machining. Don't know if that is true, but I know enough to know that flow is about much more than just valve size. Bigger is not always better.

[Kelley W King]

My experience tells me you need the cam for the big valves to work and vice versu. I tried to build a L79 with a 327 300. I used the pistons, cam, intake and carb but used the 1.94 heads. It did not work. Changed the heads to 2.02,s and the motor really lit up.