360 swap to 318

[Danpd69]

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

[PwrWgnDrvr]

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.

[Wildergarten]

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.

[PwrWgnDrvr]

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)

[Wildergarten]

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.

[PwrWgnDrvr]

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.

[Wildergarten]

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.

[PwrWgnDrvr]

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.

[Jim100]

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

[Danpd69]

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

[Wildergarten]

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.

[Jim100]

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.

[Wildergarten]

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.

[Mojunk]

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.