318 or 318 ?? which one

dodgedartgt said

IIRC, the '68-70 318 was rated at 230hp. And the '74 was about 125hp(?).. Not an inconsequential number I drove (long term) both a '70 Swinger and a '75 Duster. The performance differences were much more than "minor".

A previous poster suggeted that the '74 engine would have hardened exhaust seats. If this is more than just an occassional driver, personally, I would consider swapping on the later heads. At the same time, consider swapping in a set of aftermarket roller lifters and comparable cam, along with a decent 4bbl intake and carb. For a relatively small investment, you should see some real improvements, possibly even exceeding 300hp.

My .02 cents.
Mike in FL

Click to expand...

Aftermarket roller conversion is more than a small investment...the lifters alone are like $400, then you have to run the cam to match them if the base circle is different...then throw in the fact you'll need shorter pushrods to offset the longer lifters. For a stock engine, that's really a little much...you'd be better off buying a running magnum if you want the roller cam that bad.

And as 66fs said, the hp ratings differ due to hp measurement methods. The only thing different between a '69 and a '74 2bbl 318 is the pistons in the '69 are like .020" taller, which give it a smidge more compression. But, 68-74 all used 675 heads unless someone swapped them. If your 75 ran significantly different than your '70, the '75 does use different head casting and probably has a smog pump on it...little different setup.