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Poly/LA 318

Moparts Member
Posts: 2513
From: Sicamous, B.C., CANADA
Registered: Sep 2001
posted 07-02-2002 05:19 AM

Just got given a Poly 318 and an LA 318 both with 727's behind them. Will the 727 from the poly go behind an LA engine? As well, what's the deal with the crank? Were they forged? Will they go into those LA engines? Rods? Pistons? How much of that stuff is worth hanging onto?

Moparts Member
Posts: 741
From: moscow pa. u.s.a.
Registered: Apr 2001
posted 07-02-2002 05:35 AM

trannys will interchange. polys have steel cranks and will interchange with la`s. i`ve heard that poly conn rods are lighter. pistons should be the same. you can bore a poly .1 too! with a 4in stroker crank! makes an sweet 318 lol. there was a build up in mopar muscle a few months back. check it out!
now just sit back and wait for someone to chime in with the old "get a 360" song and dance, all you have to do is say 318 and they will come a runnin!

Moparts Member
Posts: 747
From: NH
Registered: Jan 2000
posted 07-02-2002 09:50 AM

I have a poly 325. I was considering building one for torque and putting it in a truck. It would more or less bolt in place of a 318, wouldn't it? I think I'd have to leave the dual plane two barrel manifold on it though, just cause it's cool.
Maybe throw a 590 two barrel on it.

New Member
Posts: 76
From: Virginia Beach, Virginia USA
Registered: Sep 2001
posted 07-02-2002 11:15 AM

Questions regarding the Polys can usually be answered on 1962to1965mopar.ornocar.com. Join the "Members" list (free) and fire away. Good source for high performance info also.

Mark Nixon
Moparts Member
Posts: 4282
From: Just this side of reality, South 340 miles....In NEBRASKA!!
Registered: Jul 2000
posted 07-02-2002 11:28 AM

Gotta' watch the Poly trannies!!
The driver's side main bolt, above the starter, on SOME of them are half a bolt hole off in some years, as compared to the LA engines. They'll fit, the dowel pin even lines up, but the hole is HALF off.
I found this out the HARD way years back.
The cranks are 100% interchangable between the "LA" a "Poly" engines, just be sure that if you run a '68 up automatic, the end of the crank needs machined out for the larger convertor hub.
Also, IF you could find a Standard "LA" 318 block, the "Poly" CAR (Must be CAR!) pistons yield about 9.5:1 compression with a 360 "J" head and NO milling.

Because before I woke up to a 340, I had ONE LA 318 that I built with poly pistons that pulled as good as any 318 ever could.
The biggest expense was cutting some small reliefs in the pistons just to be SURE the .480 lift cam I used would clear.
I will also say THAT 318 would rev as good as any 340 ever could and I used 1.88 valves and stock 340 "HP" manifolds on it.

Given no $$, a 318 WILL run and run well.


Moparts Member
Posts: 1719
From: lewiston ID
Registered: Dec 1999
posted 07-02-2002 08:19 PM

didn't the '65 and 66('67 in canada) poly 318s have the larger converter hub on the crank?? I have a '65 crank and I thought it had the larger hole...I could be wrong.

yup,what he said...I always keep a lookout for the old polys. grab those steel cranks! full floating rods too.

Moparts Member
Posts: 677
From: vermont
Registered: Dec 1999
posted 07-02-2002 09:05 PM

The 325 poly has an extended crank, as well as the 8 bolt flange. These engines can be converted to a 325 hemi using correct Dodge hemi heads and pistons.
To use a late 727, you will need an adapter
Early Hemi Adapters...I mean Parts

Moparts Member
Posts: 6871
From: Eagle Creek, OR U.S.A.
Registered: Nov 1999
posted 07-02-2002 09:19 PM

ALL poly 318's had the offset bolt hole on the drivers side, and all had the forged cranks. All poly's with automatics had the large diameter hub recess of rthe torque converter. The 3 speed manual versions however, seemed to be a mixed grab bag of whatever they had lying around. Ask me, I know!!! Dennis

New Member
Posts: 55
From: Atlanta, GA
Registered: Nov 2001
posted 07-03-2002 12:30 AM

MM SEP 2001 318 Poly Hop-Ups
MM JUN 2001 400HP Poly 318
Got one in the shop. Used when i get it had it for 26 years still runs good,like a 225 can't kill it.

Steel Crank
Floating rods
Solid Lifter
diff mount mount Lug
Semi hemi heads
Hi comp Pistons
water inlet drivers side
little heavy wide block
manifold little harder to find
Check the magazines out lots of info.

Mark Nixon
Moparts Member
Posts: 4282
From: Just this side of reality, South 340 miles....In NEBRASKA!!
Registered: Jul 2000
posted 07-03-2002 08:14 PM

"...I assume that you meant 9.5:1 with a "standard" .039 head gasket??
It was calculated using a Felpro Blue head gasket. I'm certain the compressed thickness on those IS @ .039.

Don't laugh, 4speeds, I've thought about neutral balance and the pre-'73 273/318 connecting rod in a 360, with a lightweight piston. I've YET to hear of a ROD in one of those earlier 273/318 engines breaking due to hard usage, only due to spun bearings and incidental damage..

Just think, 350 Chebbies use a similar sized (Dimensionally) rod with fairly good results, given good rod bolts.


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