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Hello all,

Currently own a 1971 W100 that is running a 1973 360 V8 which replaced the original 318. The motor runs OK, but is getting tired, smokes when cold and has a vibration between 1300-1400 RPM (I know it's engine related and not drivetrain related). I'm slowly tackling projects on this truck, and next up is replacing the shot NP205 t-case. I'm buying a good used unit from a 1970, and for very little money I can get the 318 from the same truck.

I was initially planning on rebuilding the 360, but I have been thinking about going back to stock and getting this 318 and rebuilding it instead. When I do the rebuild on either the 360 or the 318 I'm going to "warm it up" a bit with a cam, 4BBL, intake and headers.

Would like opinions. Would you rebuild the 360 or go original and put a 318 back where it belongs?

Thanks!

Dan

Did the balanced flywheel/flexplate for the 360 get installed along with it? The vibration mentioned is very possible due to the wrong unbalanced 318 part being left in.

The 318 has smaller valves. OTOH, it has a forged crank and internal balancing while the 360 has a cast crank (if I recall correctly) and external balancing. So if you want this thing to breathe for high RPM performance, blowing the dough to get a 360 to take it is the better option (starting with a forged crank). If you want a reliable stockish motor that can take a lot of grief, I'd go with the 318 and put good exhaust valves and hard seats in it with a roller cam and a windage tray.

At one time in the deep past, I looked into putting 340 heads on a 318, but would have had to mill the head for compression and relieve the pistons for the valves to clear. What I can say is that tuning fuel is so important that taking the time with a smaller motor would probably deliver more torque than a stock 360.

My 70 W200 LA318, bought from GSA in 78 with 60K miles had a cast crank. Broke on the freeway at 60 mph in 86. Never have seen an LA318 with a forged crank, except the one I put in. Son had a 70 W200 with an LA318. That cast crank broke too - into 7 pieces! (parked in the driveway)

PwrWgnDrvr wrote: ↑

Wed May 20, 2020 10:57 pm

Never have seen an LA318 with a forged crank, except the one I put in.

Strange, I'd been told mine was steel by the machinist who'd ground it.
Mopar did make steel cranks for some of the LA motors, particularly the 340: http://www.mopar1.us/casting.html
Not all of the LA production history is listed in this table.

Scan of a Mopar small block book in this link shows 273/318 cranks from 68 on are all cast:
https://www.forabodiesonly.com/mopar/th ... 318.33424/
Comments in the various posts prior to the scan are all over the place.

PwrWgnDrvr wrote: ↑

Thu May 21, 2020 8:14 am

Scan of a Mopar small block book in this link shows 273/318 cranks from 68 on are all cast:
https://www.forabodiesonly.com/mopar/th ... 318.33424/
Comments in the various posts prior to the scan are all over the place.

This was a '64.

Wildergarten wrote: ↑

Thu May 21, 2020 11:37 am

PwrWgnDrvr wrote: ↑

Thu May 21, 2020 8:14 am

Scan of a Mopar small block book in this link shows 273/318 cranks from 68 on are all cast:
https://www.forabodiesonly.com/mopar/th ... 318.33424/
Comments in the various posts prior to the scan are all over the place.

This was a '64.

What was a 64? I don't see "64" mentioned in any posts on this thread.
64 318 would be an A block and of course, the polys are all forged cranks. The discussion is about LA 318's and the original poster was asking about his 73 318 in a 71 truck.

If the flywheel on the 360 is correct then all things equal I guess I personally would rebuild the 360. Not that there is anything wrong with that 318.
Either would probably serve you just fine. Yeah that really helped!
jim

Thanks for the responses all.

The 360 was installed in the truck by the previous owner (God only know how long ago). I don't know if they utilized the correct flywheel, but wouldn't I get a vibration all the time and not just between 1300-1400 RPM? Truck drives down the road at 50ish turning 2500 RPM without any issue, but while sitting still if I rev the engine up between 13-1400RPM you can feel the vibration through the steering wheel, see the exhaust rattling, etc.

I know the 318 had higher compression (8.8 vs 8.4 on the 360 I believe), but I imagine the extra 42 cubic inches with some performance goodies would still outshine the 318 with the same bolt ons?

Thanks again,

Dan

PwrWgnDrvr wrote: ↑

Thu May 21, 2020 1:08 pm

What was a 64? I don't see "64" mentioned in any posts on this thread.

It was the '64 Dart 270 wagon I had with an LA273 and three-on-the-tree which the machinist said had a steel crank.
Great car, but the 9" clutch and brakes were a joke. I did throw a rod in it one day and replaced it with an LA 318.
I converted that car to a 4-speed hurst and a racing clutch with, disks, 8-3/4" 2.93 rear axle, dual exhausts and a tricked out Holley. Man did it go. Porches were my favorite prey (an SC was a push). Put 180,000 brutal miles on that junkyard motor, yet when I pulled it down there was almost no ridge.

When I installed my 360 here in Michigan about 20 years ago I had a hard time finding the also differently balanced harmonic balancer because the 360 was so popular with some kind of race car builders. I would imagine more zip from a similarly prepared 360 than 318.

Jim100 wrote: ↑

Thu May 21, 2020 3:48 pm

When I installed my 360 here in Michigan about 20 years ago I had a hard time finding the also differently balanced harmonic balancer because the 360 was so popular with some kind of race car builders. I would imagine more zip from a similarly prepared 360 than 318.

The 340 was the better motor. It had 2.02 intake valves compared to the 360's 1.88. The TA/AAR motor in particular was completely different: thicker pan rails, different rocker geometry to accommodate larger ports, and of course the legendary 6-pack. For one brief shining month I had a 340 for purposes of a rebuild for my dream Dart I never finished; it was ripped off from where I was living in Culver City.

I've torn apart several D500 and D600 trucks and the LA318s had steel cranks. I believe they are called 318-3 cranks. The 62 and newer poly steel crank works fine in the LA motors, you just have to mark top dead center on the LA balancer as it is in a different position. The 318 flywheel on a 360 does create a vibration, but it isn't near as bad as a 318 torque converter on a 360 for some reason. I have a friend that's lived with that vibration for years. Not my thing though. My vote would be for a 318, I love them. Built with compression and a decent set of heads they perform well, last forever and get good fuel mileage.