1965 mopar 273 heads

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saskatchewan

saskatchewan

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Hi

This may sound like a strange question, but, is it possible to swap later 318 or 360 heads onto an old 1965 or earlier 273? My thinking is with respect to the issue of older "soft" valve seats and problems finding a four barrel intake manifold.

Thanks
 
Yes, the heads will bolt on.

However, I would recommend using the 318 heads as they have smaller combustion chambers so you don't lower your compression too much.

The 340/360 heads have larger combustion chambers which can lower your compression by 1.2 - 1.5 points.

The early 273 heads had smaller combustion chambers, so even putting a 66 318 head will drop the compression a little, but not too bad.

I would find a set of early 66 -69 273/318 heads and have hardened seats put in them, or the 302 later castings as they have reasonable chambers, but I'm not sure how much to keep your compression from dropping...
 
Thanks for the great information. The drop in compression would be a concern, but, until I try the combination I guess I really can only guess how much of an effect it might have.
 
If you do a late model head, I would recommend looking for a pair of 302's; last 3 digits of the casting number; find them on 2bbl 318's in 85 to 87 Diplomats, Grand Fury's. Tight chambers, good flow, a nice upgrade to a 273.

Good luck!
 
I would caution using newer 318 heads. Your driver's side exhaust manifold will interfere with an extra coolant "bump" on the newer head.
 
Would it be possible to substitute a set of generic shorty headers to get around the "bump" problem?
 
saskatchewan said:
Hi

This may sound like a strange question, but, is it possible to swap later 318 or 360 heads onto an old 1965 or earlier 273? My thinking is with respect to the issue of older "soft" valve seats and problems finding a four barrel intake manifold.

Thanks
Click to expand...

Possibly not. Some of the early 273s had a different angle for bolting on the intake manifold than the later ones. All of the LA heads from 66 on have the same bolt angle. IDK when the change was made, end of MY or a running change during the 65 model year. This does not affect the heads fitting, but if the existing heads have the earlier LA bolt angle, the the intake will not fit the newer heads.

The 318 and 360 heads have different intake passages. This may affect the selection of intake manifolds.

If there is an issue with hood clearance and a Commando air filter housing with a modern dual plane manifold, you can change the air filter element. The Commando air filter is taller but is the same diameter as the slant six using the round black housing that looks like an unchromed Commando one.
 
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