Well, not knowing too much about the engine bay of that particular car,
its hard to say. And in general Mopar swaps aren't always "easy" because
of the rear distributor on the LA smallblocks, the size of the
big-blocks, and the overall size of most of the v8-capable automatic
trannies. Both the TH200r4 or 700R4 are quite a bit smaller than the
A-500 and A-518 Mopar 4-speed ODs. For those reasons I'd probably
abandon my "roots" and not even consider a B/RB big-block (383, 440) or
an LA smallblock (318/340/360).
Without knowing too many details, here's what I would probably dig
1) a turbo 4-cylinder Mopar from a FWD 80s Mopar, coupled to a RWD
transmission from a late 80s Dakota (when the Dakota also used the 2.5
common-block engine that the FWDs used). The FWD Mopar guys get
stupid-huge horsepower out of 2.2/2.5 turbo engines by putting on big
intercoolers, big injectors, aftermarket turbos, etc. and the engines
take the pounding very well (same bearing sizes as a 426 Hemi or 440).
And they aggravate the bloody heck out of us muscle-car guys by getting
25+ mpg when they're not spooled up and running 12-second quarter miles.
I never know whether to consider them buzzing little pests, or amazingly
2) A modern Hemi (5.7) which is sold as a crate engine complete with
engine control computer (or carburetor and simplistic distributorless
ignition controller if you go low-tech). Its nice and compact without a
distributor sticking out anywhere, and narrower/lower (for the most
part) than OHC v8s like the Ford Modular and Mopar 4.7. Actually
size-wise its pretty similar to a GM Gen-III v8. It will mate up to any
smallblock Mopar transmission bellhousing, so you can go
old-school/bulletproof with an A-727, or you can go with a 90's A-518 OD
transmission from a Ram, if it would fit under the floorpan. Or get
creative and use a stick.
Either option would require a lot of fabrication, but the turbo
4-cylinder would almost certainly fit with room to spare. Something
really out there like a fuel-injected slant-6 would be beyond cool, but
I wonder whether there's enough room for a long American inline-6, and
it certainly would be a DIY fuel injection setup and nothing that's OBD
A Jeep 4.0-liter straight out of a circa-2000 Cherokee would be a
contender in the "low bucks/ use it exactly as it comes out of the
donor" category if there is room. Those are extremely torquey and would
make for a peppy driver.
Since you want a newer engine and I expect you would like decent mileage
I would probably look into using an adapter plate with the factory trans
and use a 3800. The 4.3 is a great engine but gas mileage is not it's
strong suit. Get a 3800 from a later vehicle and use an adapter plate to
bolt it in. Just find a machine shop to make one.
Conversions, especially ones where there isn't prior development work
already done for you, can be very costly and problematic. I don't know
what the weight of the original engine is, but you would want to make
sure that any replacement isn't significantly heavier or the handling
and braking can be severely compromised.
If you really must do this, by all means I would stay away from the
2.9/3.1/3.4l family of engines. I don't know if they were ever made for
rear wheel drive or not, so it might be a moot point. Packaging
efficiency is very good, but problems like leaking intake manifold
gaskets and other make for a less than ultra-long-life design.
The 3800 from a later model Camaro or Firebird donor would be the first
thing I would look at if I just had to make the conversion. Other
possibilities might be the V-6 Mustang motor and transmission from 1990s
vintage stangs. Lots of fabrication and making do would be involved in
such a swap.
Lots of folks have done GM swaps into Volvos, Jaguars and Jeeps, but I
haven't seen much written about doing so into an MB product.
Personally I would tear down the original MB motor and make it right.
The cost and headache will probably be lower in the end than using low
cost GM parts as the basis for a swap.
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