The 360 Magnum engine is nice but there are several differences between the Magnum engines and the LA small blocks.... I'm pretty sure the truck style exhaust manifolds for the LA small blocks are the same and interchangeable.
I realize this is an older post but it came up in a recent search about manifolds and perhaps needs clarification.
The quote above is semi-correct if we include the late '60's-late 80's engines. Am unfamiliar with the newer 360 magnums. The exhaust manifolds on pre-magnum small-block LA engines (273/318/340/360) will interchange in the sense they will bolt up to each other. HOWEVER,,,, each size engine has its own specifically-engineered exhaust manifold set. The larger the displacement, the larger the ports. The only exception might be the 273/318 size since I do not know for sure between those two. But I DO KNOW FOR SURE the 340 manifolds and heads have larger ports than a 318. Likewise, the 360 also has larger-ported heads with matching larger-port exhaust manifolds. You can certainly put a 360 exhaust manifold on a 318 but you're gonna blow the manifold gaskets fairly soon if the truck works hard. I realize the gaskets may be the same part number but the mating surface is thinner when a 360 manifold is put on a 318. The machined surface area is different. Behind the cobwebs in my memory I think there once was an article about this in Mopar Magazine in the 70's or 80's.
Exh manifold gaskets seem to almost always fail on the passenger side first. I attribute this to the automatic manifold damper and the pressure it creates, especially in very cold weather. I have had dampers get stuck closed as well. Gasket blowing seems to almost vanish on mopars with the damper removed or with headers, or as someone here mentioned, replace the RH manifold with a spare LH manifold. Perfect!
Mods I did in the 1970's-80's were putting 360 heads/manifolds/intake on a "Low-budget HiPer" 318 to help it breath better, and 340/4bbl intakes on 318's and 360's. But with these mods there are carburation variables that need to be worked out. I also have run 318 heads on a rebuilt 360 (bored to 383ci) for a few months with no troubles and hardly any loss of power during normal driving, while rebuilding the 360 heads in my spare time.
True, there are a lot of components that interchange among SB-LA engines. Except the 360 has it's own oil pan (all 4x4 and 4x2 oil pans are also different) and 360's use a different model 727 than a 318. The 360 is truly an externally-balanced engine unlike the other SB's. I found that out the hard way in 1980 when a failed fuel pump seal ruined my 3yo 318. I put the 318's like-new flywheel/clutch/pp onto a replacement 360 that came bare. All was fine except whenever the rpm's went above 1800. Like the old song, a whole lotta shakin' going on!
As has been mentioned previously in this topic, 360's do have their own dedicated (balanced) torque converters, flywheels, and their own balanced crankshaft pulley. Sure these parts will bolt up to other SB engines, but it will be quick to let you know that it is not happy.
Slightly off-topic but deserves mentioning: Big Block engines also use a 727 automatic tranny. But that 727 is not interchangeable with small-block 727's, they absolutely will not bolt up. Just like the difference between SB/BB flywheel housings, the bolt-pattern diameter on a BB 727 is noticeably larger. I have had success putting small-block powerplants/trannys into 1970's vehicles originally big-blocked. As long as the recipient and donor were the same body type, don't have to relocate motor mounts nor tranny mounts nor do any body or frame mod. Have also converted automatics (including M880's) to standard, and vise-versa, without difficulty nor changing mounts.
On automatic tranny vehicles, SB driveshafts have a smaller-diameter input spline than a BB. It was smart to grab the donor's driveshaft too, even if the wheelbases were different. Usually rear-axle input yokes were the same size so you didn't have to change those out as long as the swap was to a similar class. (powerwagon to powerwagon, Ramcharger to Trail Duster, Sebring to Roadrunner to Charger, or Duster to Demon etc.)
Hope these experiments from 30+ years ago help someone out there
