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318 LM and poly cranks and Poly cylinder walls #2612398 01/26/19 01:52 AM 01/26/19 01:52 AM
Joined: Dec 2015 Posts: 11 South Australia R Retroboy OP member
Retroboy OP member R Joined: Dec 2015 Posts: 11 South Australia	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

Re: 318 LM and poly cranks and Poly cylinder walls [Re: Retroboy] #2612419 01/26/19 03:11 AM 01/26/19 03:11 AM
Joined: Nov 2007 Posts: 21,814 Kirkland, Washington Pacnorthcuda Too Many Posts
Pacnorthcuda Too Many Posts Joined: Nov 2007 Posts: 21,814 Kirkland, Washington	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.

Re: 318 LM and poly cranks and Poly cylinder walls [Re: Retroboy] #2612459 01/26/19 10:05 AM 01/26/19 10:05 AM
Joined: May 2003 Posts: 6,559 Downtown Roebuck Ont Twostick Still wishing...
Twostick Still wishing... Joined: May 2003 Posts: 6,559 Downtown Roebuck Ont	My understanding is a poly can be bored .100" without issue. A sonic check would confirm for you. Kevin

Re: 318 LM and poly cranks and Poly cylinder walls [Re: Retroboy] #2612467 01/26/19 10:41 AM 01/26/19 10:41 AM
Joined: Dec 2009 Posts: 284 STL ,MO H Handygun enthusiast
Handygun enthusiast H Joined: Dec 2009 Posts: 284 STL ,MO	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.

Re: 318 LM and poly cranks and Poly cylinder walls [Re: Retroboy] #2612496 01/26/19 11:58 AM 01/26/19 11:58 AM
Joined: Jan 2003 Posts: 1,335 Oregon E earlymopar pro stock
earlymopar pro stock E Joined: Jan 2003 Posts: 1,335 Oregon	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

Re: 318 LM and poly cranks and Poly cylinder walls [Re: Retroboy] #2612504 01/26/19 12:20 PM 01/26/19 12:20 PM
Joined: Dec 2009 Posts: 284 STL ,MO H Handygun enthusiast
Handygun enthusiast H Joined: Dec 2009 Posts: 284 STL ,MO	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.

Re: 318 LM and poly cranks and Poly cylinder walls [Re: Retroboy] #2612510 01/26/19 12:34 PM 01/26/19 12:34 PM
Joined: Oct 2007 Posts: 4,205 New York polyspheric master
polyspheric master Joined: Oct 2007 Posts: 4,205 New York	Poly only has conventional 6 bolt (LA) crank flange 1962-66, earlier is 8 bolt. Boffin Emeritus

Re: 318 LM and poly cranks and Poly cylinder walls [Re: Retroboy] #2612539 01/26/19 01:27 PM 01/26/19 01:27 PM
Joined: Oct 2008 Posts: 1,176 East Coast A A/MP super stock
A/MP super stock A Joined: Oct 2008 Posts: 1,176 East Coast	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.

Re: 318 LM and poly cranks and Poly cylinder walls [Re: Twostick] #2612554 01/26/19 02:03 PM 01/26/19 02:03 PM
Joined: Dec 2003 Posts: 22,695 Bitopia J jcc If you can't dazzle em with diamonds..
jcc If you can't dazzle em with diamonds.. J Joined: Dec 2003 Posts: 22,695 Bitopia	Originally Posted By Twostick My understanding is a poly can be bored .100" without issue. A sonic check would confirm for you. Kevin And lighten the anchor while at it. Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.

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