partsman1965
Well-Known Member
Will 318 poly block fit/interchange with other Mopar BB or LA engines?
318 POLY
- Thread starter partsman1965
- Start date
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318 poly is the A block
273, later 318, 340, 360 are LA block.
oil pump, timing chain and gears interchange, oil pan(not 360), front cover & water pump are year specific.
crankshafts including strokers will work with the 273-340 Journal.
You can bore the block to 4in. or a little more as in 340 bore size.
Same bellhousing bolt pattern as the LA.
273, later 318, 340, 360 are LA block.
oil pump, timing chain and gears interchange, oil pan(not 360), front cover & water pump are year specific.
crankshafts including strokers will work with the 273-340 Journal.
You can bore the block to 4in. or a little more as in 340 bore size.
Same bellhousing bolt pattern as the LA.
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My uncle has one of those, he has been begging me to come and get it out of his garage.
Get it, bore it, stroke it, port it. Their head design makes more torque than the LA.
Make a 408-426 poly.
Just something I would like to do someday.
I was thinking about grabbing it, I need a crank for a parts motor 340 I have.
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They do have forged cranks in them.
I know, not sure how off they are on balance on a 71 340.
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Nothing rebalancing won't cure.
I thought all 318s had lighter pistons and Rod assemblies and therefore you had to add weight to the crank to use in a 340.
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Drivers side lower bellhousing bolt hole location in a different spot than the "LA" version, if cross breading to the "LA" transmission.
Good notation Jadaharabi.
While the front cover is different than later year LA’s, the earlier year LA is the same. (IIRC)
But they will bolt on without issue. The catch is the Alternator mounting. If you use a later year LA cover, you’ll need to also swap Alternator brackets.
Also timing marks are on the other side. IIRC, I do think you can still bolt on the timing mark tab from an old engine onto the new cover.
Crankshafts from the 273,318,340 swap in BUT the rear flange can throw you a curve. Keep your eyes open and what “may” need to be done is clear. Early Poly engine cranks can be a little weird at the back.
On over bores, just sonic check before any machine work is done. Low cost to know to know for sure where you stand and how far you can go.
The Poly Head is a very nice design. The draw back is it was never cast with the areas that need to be thick for porting purposes. This limits maximum air flow available when ported. This leads to a high velocity small port that creates big torque on these builds. Especially stroker’s.
Being a old outdated engine that never got the nod from Mom MoPar on hp parts, the after market only made a small sprinkling of hp parts. Currently TTI is the only (and thankfully worthy) header manufacturer (that I know of) and “Chrysler Power” has a new intake (RPM-ish in design) and there are a few companies that will have camshafts for the engine. Being there a IE-IE-IE-IE pattern.
Lastly, as far as I know, Egge Machine has cast pistons for a Poly. But I don’t know who else.
Also, the distributor, intermediate shaft, lifters, block hardware (though slightly different in amount and locations) are also swapable. Gaskets except intake, balancer with exception to timing mark location, bearings, crank and rod and most attaching bolts can be swapped.
The Poly and LA do look different but are very similar.
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