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Just curious if anyone out there has swapped a more modern GM Atlas family 4/5/6 inline in their truck from an early Colorado. Trailblazer, bravado etc. Even the 4 cylinder shows specs that would be great in my ‘37 if I ever needed the 216 replaced and the 5 cylinder appears would fit in length with no modifications as well.

37 GC
Can't answer your question but.... I have owned & driven a 06 Colorado with 4 cyl over 200,000 miles now without problem one.... I am a believer in those motors.. Owned since new... suppose the 5 cyl would be similar....got me some great gas mileage since new.... Delky Dave in (snowy) central WYO

Very interesting question. Moved the post from General Truck to HiPo forum. Think you'll get more / better input here.

I have looked at the idea a few times. The biggest concern I have with the 5 cylinder is the dimensions. It is both longer and taller than it seems like it should ve from the specs.

I would recommend taking some measurements off one in "full dress" to see how well it would fit your engine bay.

I assumed the 6 was definitely too long. Looked like the 5 may fit but haven’t actually measured. The 6 may even work with a little firewall work, you’d think less than a big block. 242 horse beats any 261 or 292 stock potential

I, for one, am all in favor of this project. My only request would be that you take pictures and document it.

I'm in the "drawing board" stages of putting a 4.2 DOHC cylinder head on a 261 stovebolt block. The problem you're going to encounter with running the complete engine is all the computer controls involved. I've also investigated the possibility of turning the 4.2 into a "dumb" engine with a carburetor, a distributor, and fixed exhaust cam timing. I think both ideas are worth some more attention. That oddball oil pan with the axle shaft tunnel through it would also have to be modified for front axle clearance.
Jerry

I knew the electronics would add to the fun. Haven’t looked at the oil pan. I wonder if all three (4/5/6) are all the same in that aspect.

The Atlas engines use the P10 ECU. Making that run standalone is trivially easy.

The 4 and 5 cylinders had a rear sump oil pan. The 6 cylinder had a front sump.

You would probably need the rear sump for your truck.

Fibonachu nailed it. I looked into a atlas setup just for fun before i did my LS setup. I know i 100% always love my LS’s but was always curious on the atlas series and it basically removes the v8 steering box clearance issues. The ecu and harness setup is very similar to early LS platforms which is super easy to deal with. Anyone with HPtuners software can make it work easily. I simply was in too much of a rush to get mine done before my son was born so the junkyard down the street with the $400 5.3 on a pallet was just to easy to ignore and I already know them well. I do follow a few people experimenting with the atlas in turbo drag racing applications and they seem to do really well even in stock form. One of the nelsons had one hold up well at a drag week or other drag and drive event I believe. They have pushed them to break too but everything has its weak links. I say go for it. Should be a good fit and fairly simple.

I have seen the 6 cylinder #3 and # 4 rod bearings go bad on 2 separate occasions. Both engines were in the 120K mileage range and both had routine maintenance records. I was not sure if it was oil flow problem or just a bearing failure, it did ruin the crankshaft in both cases. The only other issues I have encountered were with the variable valve timing circuit. The engine would have a code and the sensor would test fine. I have seen more than one sensor replaced only to have the code come back within a 1000 miles. I believe a good block flush may have restored oil control to the sensor and cleared the problem. As I was not the Tech working on the engine they just kept changing the sensor, same problem each time.

I've been doing some measuring on a cylinder head I've got in the "possibles bag" like the oldtime mountain men used to call the place they stored miscellaneous junk. It looks like it won't be much of a challenge to convert it to a dry belt drive and eliminate the variable cam timing altogether. I believe that adapting an Atlas 4.2L head to a 261 block has some possibilities.
Jerry

Tuts 59 makes a good point. Those engines are fairly famous for clogging the variable timing systems, then starving other areas for oil.

My intention when I looked at them had been to pull the variable timing system out. I never got as far as figuring out how to do that before going back to my LS setups though. Hotrod Lincoln's suggestion seems like a reasonable plan if you did want to pursue it.

The early Chevy and Pontiac 2.8L V6 had a similar problem with burning rod bearings near the center of the crankshaft. I found that when the oil passages in the block were drilled from each end when the blocks were machined, they didn't quite intersect- - - -creating an oil flow restriction at the center main bearing that resulted in the rods pressurized from the center main to be starved for lubrication. We made up a long drill bit to chase out the oil galleries when we rebuilt those engines.
Jerry

@DIYEFI did a swap here in stovebolt 14 years ago

Does the Atlas bell housing bolt pattern interchange with any other GM engine? Specifically, would there be a standard shift bellhousing, flywheel, clutch, etc. to marry the engine up to a 5 speed OD transmission without a bunch of expensive adapting being done?
Jerry

No.

Per the internet, the Atlas engines use an Aisin bolt pattern. Adapters are available to the SBC or metric bellhousings, but those are not what you were asking for.

The oil issue is not limited to the Atlas engines either. I recently replaced the VVT actuator assy. on a Honda SUV at 207,000 mi. that had had normal maintenance according to the owner. It set a code consistent with the pressure switch failure noted in a Honda TSB. I replaced that and the code came back a few days later. So I replaced the actuator. It was full of sludge. Maybe I could have cleaned it but I'd already bought the new one.

Most of the new emission-controlled diesels will sludge up regardless of factory-specified oil-change intervals, resulting in oil-starved top ends and some crank bearings. Change Your Oil. Change Your Oil.Change Your Oil.