318 heads and combustion chamber size

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ProStocker273

ProStocker273

MoPar N Jeep
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I have a cracked head on the from side near drivers mount. Weaps coolant but not getting into oil. They are 920 318 heads.
My dads buddy has a few sets but only info I got was they have hardened seats. I am only familiar with the 675, 920, 302 as far as numbers go. I know they are not 302s as he has a set and won't part with them. What other 318 heads are there that would have hardened seats and are they closed chambered? My motor can't afford to lose any compression. Also would later 318 heads have the larger pushrod holes and air injection holes? I have a how to hotrod small blocks book but can't seem to loacate at the moment.
 
You need to post more information for someone to help you.

What year is the 318 that you are working on?


What casting number heads do you have on it now?


From you mentioning about an air pump, I will assume it is a later 70's or 80's engine.

You can swap any year 273/318 head on there EXCEPT '64 & 65 year heads as they have different angle intake manifold bolts. So you can use any heads from 66 to mid 80's for sure (i'm not sure about the magnum heads).

If you do some research, I believe that the 66 or 67 heads may have smaller combustion chambers that what you are running which may help your compression. As far as hardened exhaust valve seats, you can have any head machining shop install them so you can run pump (nonleaded) gas.


You can also have the heads improved by porting the heads and also if you wish, have the 360 valves installed if you have the valve jobs done and hardened seats put in. A little porting and some larger valves can wake up a 318.

Also I recommend using matched sets of heads with the same casting numbers, don't just buy one that doesn't match the other side casting number to keep everything even.
 
You must not have read my post. I know not to miss match heads. Common sense. I have 920 heads with a crack. I need new heads but not sure if later headz that would have hardened seats would be open chamber my motor is 66 273. I don't want open chamber want to keep my compression close to were it is now with 920 heads. The heads my dad friend says he has have hardened seats so Im trying to figure out what heads would have those. Then secondly do all heads produced after the 920s have the large pushrod holes and air injection? I personaly don't care if they do or not. Not the point just curious about combustion chambers on 70s and 80s heads that have hardened seats..
 
So my questions.
Did all 318s have closed combustion chambers?
What years had open combustion chambers?
What is the cc difference on open chambers?
Do all 318 heads produced after the 920s have air injection holes and large pushrod holes?
 
ProStocker273 said:
So my questions. Did all 318s have closed combustion chambers? What years had open combustion chambers? What is the cc difference on open chambers? Do all 318 heads produced after the 920s have air injection holes and large pushrod holes?
Click to expand...

These answers are only to my minimal experience.

1) nope
2) 68-84 open chambers, 85-up (minus some apps) mostly used 302 castings, which of course were closed chamber; magnums are also all close chamber
3)open chambers are advertised 68cc if memory serves, and closed should be 63-65cc as cast.
4)...need Hebrews or skrews to answer that one accurately...
 
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