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They're both 12v engines but I was wondering if there are any major differences?

Early USA 91 and 93 164 engines yes have some differences. early engines have coarse threaded bolts and crankshaft bolt holes for mounting flywheel. early engines (maybe all 91s) have deep 8 quart oil pan later 92-93 ones have shallower 7 qt pan and maybe different pick up tube.

Most 91s have different lower and mid thermostat housings than 92-93 because later engines have a steel heater return tube routed over rear valve cover instead of just hose going to steel cross over tube behind lower part of radiator.

Most 93s have oil cooler and coolant lines going to lower and mid theromstat housing whereas early 91s if not an S do not have oil cooler but later 91's do have oil cooler.

Early engines have intake manifold bolted directlyto rear valve cover later engines have intake mounted on rubber mounts screwed into valve cover and grounding strap for intake.

None are major but if doing an engine swap, heater hose and oil cooler plumbing and flywheel bolts etc., can be pesky items to make one engine fit in differently configured engine bay.
 

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Early engines have intake manifold bolted directlyto rear valve cover later engines have intake mounted on rubber mounts screwed into valve cover and grounding strap for intake.
I'm glad you mentioned that the '92 cars have a ground strap and the '91 cars don't. I thought I was going crazy. I kept thinking that there was a ground strap on the intake when I was putting my '91 S back together. It must have been a distant memory from when I worked on a friends 92 S. Is it near the throttle body?

Whew....

Paul
 

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Yes. It attaches to the left rear plenum mount (I think that technically, the intake manifold is the small piece to which the intake runners and injectors mount right at the head intake ports). The plenum has three mount points. I've seen the ground strap run to any of the nearest valve cover mounting screws from the plenum foot.

Along with the change in mounting of the steel water tube for heater flow mentioned by Steve, there is an access hole in the fender well to allow a mounting bolt to be removed with the engine in the engine bay. This is a _must_do_ for timing belt replacement, as I have not found it possible to R&R the top rear T-belt cover with the tube rigidly held in place. Just a warning in case someone has been struggling with that in times past or present.

Michael
 

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Differences; we were also never able to come up with the conclusive, final word with regards to the oil-squirters IN THE BLOCKS...!

The previous school of thought was that only S blocks had them. Then the later thought became that ALL of the later 12 valve blocks had them, regardless of model. Then I found the 91 L block with the squirters and we never revived the conversation from there.

So, yeah - you may or may not have the BLOCK squirters in the older blocks, but you DO in the newer blocks for sure (and even on a ' 91 such as what I found...) Regardless, all of the rods had squirters in them!

Also, I heard/read somewhere that some of the European models had a coil-pack (not COPs - just a coil-brick - like the Alfa 155's 3 x 2 double coil-brick), rather than the single coil that the US models had.

Don't know if this impacts your question or not, but don't forget that there was also a (non-US) V6 2.0 litre turbo variant of 12 valve 164 blocks.
 
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