318 LM and poly cranks and Poly cylinder walls

Howdy
Can anyone tell me if a 1974 318 LM has a steel crank? Also does a 318 Poly have a steel crank? I believe the poly has a heap more meat in the cylinder walls that a 318 LA. I want to build a 4 x 3.31 motor for my Slingshot with an eye toward nitro in the near future
Cheers
Tony

The 74 marine 318 will be a cast crank, the poly will be a forged. I beleive they ARE interchangeable, others can confirm or refute. Don't know on wall thickness.

My understanding is a poly can be bored .100" without issue. A sonic check would confirm for you.

Kevin

I am not a nitro engine builder but I would think of the two for several reasons the poly would make the better fuel engine and to do it at whatever would clean it up.

And in spite of the added weight of the Poly over the LA, the Poly head design is far better than most of the LA options.

- EM

We bandsawed some up awhile back IIRC there were some areas close to water in the chamber but if la is the same then I only see advantages with the poly.

Poly only has conventional 6 bolt (LA) crank flange 1962-66, earlier is 8 bolt.

That forged crank is old technology with respect to metallurgy. I believe that they are heavier that modern forged. Poly heads can produce 400-500 HP max. Now you can throw nos,tc and sc at it, but not worth it. Custom pistons and intake $3000.00+. Funky yes. Neat yes. Results mediocre from what I think you want. A 331 hemi will make more power and all the parts are available. Then there's the 354 and 392 also. There is a poly website. Check it out.

And lighten the anchor while at it.