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The tall deck 2.5L pre-dated the later (89+) 'common block' engines. It used proprietary length rods, the same pistons as a 2.2L (I think) and did not have floating wrist pins, and stock would have had an N/A compression ratio (9:1 I think).

The 89+ 2.5L engine uses the same rods, but a different crank and pistons. The pistons have the wristpin positioned higher, and the crank has greater throw - as well as a relief at the bottom of the bore to clear the rods with the larger crank throw. The 89+ is often considered stronger. The 2.5L shipped with balance shafts, which are often removed or rendered inoperable for a few HP and less mechanical complication.

If you have forged slugs and studs in that 2.5L, and dished pistons (turbo pistons, with the lower compression ratio) then you've got a great starting point. Toss a swirl head on there (ported, preferably) and enjoy the increased torque and faster spool of the 2.5L.

The only down-side to the 2.5L is that because it's bigger, it demands more flow - our 8v heads are anemic to begin with - and the 2.5L only makes the head an even bigger choke point, and move max power lower in the rpm range. With a very good flowing head, the 2.5 should have some substantial potential (it's still a driveability upgrade over a 2.2 in a heavy car).
 

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Do you have a custom cal that came with the engine? If not, you'll likely need some tuning. Porting and other flowpath improvements start to require some computer hackery.
 

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well i work at a junkyard and we had a spirit rt there with the 2.5 turbo that needed the engine and we decided to try a low mileage plain jane 2.5 and put the turbo, etc on it and it ran well and pulled great going up the road till we hit 3rd gear and it blew the rods right through the block like nothing. thats when we came to find out that the turbo engines have a heavier crank and rods and pistons and the pistons are dished to lower compression ratio. we ended up having to find a turbo engine at the end of it.
:bang head
That's only true of the turbo 2 (TII) motors which had forged cranks, better rods (same as common block, though) but the pistons were the same. All 2.5L turbo motors were commonblock (the tall deck was NA) - and all the commonblock engines were basically the same, even if turbo - except for the oil drain-back and the dish in the pistons. If you put turbo pistons into a 2.5L CB, it would run fine. The only other difference were the intake and exhaust valves - mostly the exhaust valves, which were turbo specific.

If you didn't use turbo pistons... it wouldn't last long under boost. Throwing a rod though usually doesn't happen unless it's starved for oil, boosted flat top pistons should only result in their untimely demise - but stranger things have happened.
 
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