1965 318 Poly ? Rebuild or swap to LA 318?

If you get a late 318 with cast crank you either need to use the B&M conversion flex plate thats balanced for the cast crank or add MP torque converter weights to the old converter.Easy fix.
So I know everyone wants the latest and greatest toy from the shinny magazine pages but being creative and taking old tech and applying some new tech is cool as are the old Poly motors.
The last thing I ever want to see is a row of old classic mopars with their hoods up and car after car is loaded with a 5.7 German hemi.
Dare to be differant be a hot rodder not a parts installer.Ok thats my rant forthe day.

Parts are available to rebuild the poly. If you are on a tight budget the LA would be cheaper. The poly is different and very cool. Weiand still makes a dual plane 2x4 intake for this motor. Different is good. Its nice to see a 409, a nail head, a flathead, a 331,354,392 hemi, a POLY...ect (351 cleveland is a nice change in a mustang for once also.)

ALL 318s poly or LA cast or forged are internally balanced.


Some time in production of the poly 318 the starter hole was changed. I was putting a 318 poly in a dart with a 318 LA and got it all in there and the starter would not go in. I don't remember what the difference was or if I could have just used the older starter but I didn't have on to try so I dropped a 273 in that I had on the other side of the shop. I think the motor I was trying was a 64 from a polara 4dr.

The poly has good combustion chamber shape, OK intake ports and very good exhaust ports. There are a few cam available, TTI makes headers weind intakes, and whatevr stroker kits fit in 318LAs will fit in them. Since the valves are closer to straight up and down piston to valve clearance should not be a problem. I have heard of guys going all the way to 340 size bores with them but I would get a very reputable sonic tester to test it first, even if they all could go 4.040 bore when new (not) they are 40plus years old and have corosion in them reduceing the maximum over bore. You could make a very stout 390 something stroker with them. Put in a good cam intake and port work on the intake side of the heads and it will make a killer sleeper

450hp and 500tq is not out of the realm of reality.

They make a Six-Pack set up for poly. Matter of fact I just sold a complete unit intake/carbs.

Poly Lovers, Unite!
Thanks for remembering my post. ALL 318s and 5.2 Mags, as well as all 273s are internally balanced. For sure also ANY 318 or 273 (not sure about 5.2)crank can be swapped into ANY OTHER 273 or 318 without rebalancing. So if the Poly had a crank with the smaller diameter ring for the converter, a later 318 crank can swap right in with no other changes, except the thrust bearing in the new crank's bearing set has to be the older smaller diameter one to fit the block. So the 'bay's $99.95 318 crank and kit may need a different thrust bearing to go into the Poly block.

On to the ports. I believe that if you compare the cross-section of the Poly intake port to the cross-section of the 318 (not 360) intake port you will find that the Poly has more cross-section. I also believe that the Poly head flows quite a bit more than the 135 cfm of the usual 318 port. Old-timers concur that an old 318 is a lot stouter than a new (LA) 318 for pulling a trailer. Old timers like this don't even consider the 5.2 Mag because they haven't owned a vehicle that new. I think an injected 5.2 Mag would be stronger than the Poly pulling a load.

The 4" stroker crank drops right in, rods are the same dimensionally as all LA rods, pistons need to have valve pockets for the intake valve which are different than the Wedge location.

There are two problem areas for the Poly. First is intake selection. Since Holley discontinued the Weiand 7503, there are no new intakes available. The last used Weiand 7503 I tracked on the 'bay sold for $520! There were some 2-4 intakes stock and these are decently priced but try to put carbs on them! The factory 4-barrel manifold from the 1962 is priced at about the 7503 range.

The second problem area is the camshaft selection. Crane and Isky used to make cams but not for a long time now. Chris Neilsen in Utah has a supply of cores and will grind one for you, that's who ground Pavlovich's cam. There is a smaller cam company who advertised new Poly cores about 3 years ago. Figure that the new Poly cam, lifters and pushrods will run you $400 or so. If anyone has better information chime in.

The blocks are pretty stout but Mopar casting quality rules. I would feel safe at 0.060" overbore and I believe Pavlovich's engine ended up with 4.000" pistons. But I'd UT a block before going to 4.000".

The timing set, oil pump and distributor swap from LA motors, not a problem.

Rocker Arm Specialities will rebuild the rockers.

Race Section denizen OU812 claims to have Poly head porting experience.

The Edelbrock P-600 3-2s manifold for Polys has been discontinued for ages. It is cool but uses Stromberg 97 type 3-bolt 2-barrel carbs that either leak or cost an arm and a leg to have work right. There is an aftermarket fuel injection system that looks like a 97 so that may be an option. also the 97 is back in production at cost of ~$400 each.

All for now,
R.

There is a P-300 set up for Rochester carbs also. Mine runs Ford 94's or Stromberg 97's. Surprises a lot of people.

I have seen a few P-600s go over the 'bay and have yet to see one with the Rochester bolt pattern. They are relatively rare. For those who think that Weiand is still making the 2-4s for the Poly, get real. I wish that they were still making the 7503, but that's been gone a year. I don't have a catalog old enough to show tthe Weiand 2-4 manifold. Offenhauser AFAIK never made an intake for the Plymouth Poly. They might have made intakes for Chrysler or Dodge Polys but not for the one that turned into the 318.

They are a good engine but the two problems that I talked about in an earlier postt are still there.

R.

THE 318 POLY CAN BE BORED OUT .100 AND THIS ENGINE WILL BE ONE HECK OF A STUMP PULLER

Camcraft also has cams for the poly.The cumbustion chamber is almost identical to the 2008 up 4.7L Chry V-8.The cyl heads can be ported to very close to the same numbers as an Edelbrock magnum with custom valves which are available.A friend is fabing an aluminum custom intake (single 4 bbl).Easy to stroke with available cranks.Overbore .060 easily more with sonic check.

Well worth the added expense.

I have and have owned an example of every Mopar V8 in pretty much every size, up to the late '70s. I'd stick with the Poly, good engine. Have one now with 103K, stock, excellent street motor. IIRC, the '65 Torqueflite has some 1-year-only features, primarily in the shift mechanism.
I'd be inclined to run a stock cam in a car that heavy, and find or adapt a higher-ratio rocker to get some lift; you'd maintain strong vacuum but pick up HP & TQ. Should be a junkyard or swap meet 4-bbl intake somewhere, and improving the exhaust of course helps.