jormymex74

Hi, as you know I am rebuilding my mexican 318, and I have some Questions:

Currently it has a edelbrock performer 318 intake with holley 4V 600 cfm and a performer camshaft with 204/214 duration and.420/.420 lift. I was reading and I think a compcam K20-222-3 with 218/224 duration and 462/470 lift. could be a good option. What do you think could be the advantages or disasvantages? Can I use stock valve springs? It can killed my vacumm (I have power brakes) ?

The head is stock 1975 low compression head. In México 318 was the HP option and have in 1968 high compression Head, my idea was to use KB domed pistons trying to keep compresion about 9.5:1 (my stock). What do you think? It could be good or crap? Thanks have a good day

Coronet 500

I don't understand completely what head you are going to use. Are they open or closed chamber and what is valve sizes?

IF they are closed with 1.88" intake valve minimum, a flat, notched, zero deck piston with that cam would work good but not for vacuum accessories in a heavy station wagon.

Yes change springs and check retainer to guide clearance first.

jormymex74

Ok, the original Head was closed chamber but one damaged beyond repair, and is impossible to find another stock closed chamber. I decided to buy a pair of open chamber stock 318 heads rebuild. The valve is stock 1.78, I read about to put 1.88 valves on it but i don't know if I use the dome pistons (bought thinking about maintain stock compression in an open chamber head) the reemplacement Head casting is 3769973 for 75-83 318.

jormymex74

The history is this: 1968 318 in México was HP option with closed chamber heads and 4V AVS. My car ran so fine, but the time is the time. 10 years ago I have a problem with Cooling the engine over heated and one Head was broken, the mechanic put another Head but the performance drop a lot, I put an edelbrock performer and an edelbrock cam seeking to gain peformance and it did. I always think the mechanic put a wrong spare head. For some reasons I store the car in 2009. In 2016 I Want my car back beginning with a complete rebuild of the engine. When the heads was take apart I know my fears were true I have one close and one open chamber head. What a... Well you understand. I was not able to found a closed chamber head that I can afford so I decided the other way, put domed pistons in the open chamber Heads and buy the pistons and a pair of 3769973 rebuild heads. And by last I was thinking to maintain the cam (almost new) o buy a better one

Coronet 500

You have the 318 quandary of open chamber, limited parts with trying to raise compression and build quench to reduce detonation. The easiest way to do it nowadays is with Stepped Pistons that I believe are only available for 318/390 strokers.

Taking a domed piston and massaging it and the combustion chamber to achieve .040" clearance in a portion of the whole circle is extremely time consuming. Any domed piston to raise compression with an iron head without quench in a heavy car is going to give you ignition timing fits, leave power behind and not worth the effort in my opinion.

A typical flat top notched, zero deck with closed and a .040" gasket, like every car magazine article is a better place to start and worth the effort giving optimum results.

Open chamber heads on 318's SUCK.

jormymex74

Ok I agree with you 318 open sucks, well I am going to think what to do, here with shipping, any pair of aluminum heads with closed chamber could be over 1500 us dlls. But I have a better idea now, for what to do. I will send you updates, thanks a lot for your advising. Maybe I could zero deck, flat, with open chamber and 1.88 valve. Waiting for a better time to buy close head.

TVLynn

decking the block is an option,many years ago I built a 360 decked the block .050 for a zero deck with stock pistons.. Also need to remove material from the intake side of the head or from the intake manifold for a custom fit

Coronet 500

Good thinking and what I've done in the past build your short block, the heads or manifold and even camshaft can be replaced at a later date.