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Just finished building a 3.1L for my '89 LS Trooper "Obi-Wan", and must say that I'm tickled with the results. The original 2.8L in mine had spun a rod bearing and #3 connecting rod had about 1/4" of slap in it (video to come). I pulled a transverse-mounted 3.1L from a '91 Pontiac 6000, which already had the starter mounted on the correct side. This engine only had 131k miles and was taken to pull-a-part because of a simple blown head gasket. Swapped '92 Camaro 3.1L iron head pistons into it, since the original engine had aluminum heads and deep-dish pistons. Also upgraded the cam to the Comp Cams 252 kit, but opted to use the original rocker arms to save a little bit of money (next time, I'll go ahead and order the whole kit with roller rockers). Did the smog pump delete. Bored the intake manifold to 1 3/4" and installed a 5.7L throttle body with 4.3L injectors. I upgraded to the larger diameter Exedy clutch and pressure plate from the '91 Rodeo (4WD only!!! 2WD clutch and plate won't work). Had a local shop install true dual exhaust all the way back. Purrs like a kitten and pulls like a tractor! I don't know if anyone else has used an engine from a transverse-mounted application, but I didn't want the hassle of redrilling the block to mount the starter on a 3.4L pulled from a Camaro. This could potentially open up a whole new possible source of good, low-mileage, reliable engine blocks, as they can be bored out to match or come close to a 3.4L with very little additional cost and effort. The pistons have to be swapped anyway, due to the difference in dish profile and the need to bump the compression up to cast iron head specs. I'll put pics up when I can.

EDIT: Started a new thread to document progress here. V6 swap
 

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I'm still using the original 2.8L ECM to control the timing and injector pulse, but the gains are definitely noticeable and worth it, for the cost.

Round numbers -
Engine: $225
Pistons, bearings, rings, bushings, etc.: $250
Camshaft kit: $300
Throttle body and injectors: $40
Motor mounts: $60
Cost to bore intake: $40
Cost for machine shop to clean block, rework heads, install cam bushings and freeze plugs: $200
Total: $1115

I "feel" like it has more get-up-n-go than any other first-gen V6 Trooper I've driven (although, I haven't driven Jerry Lemond's supercharged beast, yet). Can't say that I've actually put it on a dyno yet, but I can chirp the tires in third gear (the kid in me giggles when this happens). Definitely opened up some horsepower and torque. Haven't run it enough yet to get a feel for fuel economy, but that will come later, as the engine goes through the break-in period. I built it with daily driving and trailer towing in mind.
 
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