318 differences 1972/1973

jakuzzie said

Hi guys!

I just bought my first mopar. It's a 1973 Duster and it has 318 engine.
What are the main differences between the 1972 318 (230hp) and the 1973 318 (150hp)?
Which parts do i need to get the 230hp out of the 1973 318?

Thanks! :D

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Main differences are:

Drop in advertised compression ratio from 9.2:1 to 8.62:1.
Hardened valve seats on 73 & later 318.
Change in horsepower rating from gross rating to SAE net. nm9stheham has it right.

nm9stheham said

As best I can recall from those days, actually the HP rating change was still at the flywheel, not the rear wheels, but the mfrs had to start putting all the accessories on the engines and such. Prior to that, they would sometimes even measure HP without water pumps to get max HP!

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The compression ratio change was accomplished by a combination of larger cylinder head combustion chamber volume and lowering piston deck height. The "tallest" pistons were used from 67-69. Piston deck height was reduced a little bit in 1970-72 engines, but the advertised compression ratio did not change, IIRC.