Although it isn't easy, you CAN replace your 3.0L SHO engine with a 3.2L out of a 93+ Automatic SHO.
You also have a little room to bore and stroke the 3.0 motor. The SHOShop has created blocks as large as 3.6L (but are they reliable?) [No. -ed.]. If you decide to punch your 3.0 out to 3.2 and you want to use the stock 3.2 pistons, be aware that the wrist pin diameters are not the same. The 3.2 pins are a hair larger to take the load from the larger piston. All of which means you'll also need different wrist pins and connecting rods.
Thanks to Tim Dahm for originally discovering the ability to swap the 3.2L motor into an MTX SHO. It was previously thought to be impossible, but the procedure has now been repeated several times. The use of 3.0L intake cams may help produce a few extra HP at high RPMs when installed on a 3.2L motor. Has been calculated as 7HP.
3.2L MTX Swap Info Thanks to Tim Dahm:
I picked up a low mileage 93 or 94 3.2 ATX engine assembly in hopes of fitting to a 90 MTX. I've started the disassembly and comparison process:
It appears the stock 3.2 short block will work as is; the 3.2 rear head is identical externally. The 3.2 front head will require modification; all other bolt on parts must be from a 3.0 (oil pump/pan, timing belt tensioner, timing covers, all accessory brackets, motor mounts, exhaust manifolds, intake assembly, water pump, etc).
Next up, I will pull the front 3.2 head and compare combustion chamber design/volume with a 3.0 head.
I've gotten a bit further into my 3.2 vs 3.0 comparison. I noted in my previous post that the 3.2 front head needs modification to use in a MTX car.
Summary: So far so good, no major problems yet - looks like I can even use the 3.2 heads with the above modification. For those who didn't see my previous post, I already confirmed that the MTX flywheel bolts right up to the 3.2 crank, the MTX-IV transaxle bolts right up to the 3.2 block, and both front and rear 3.0 motor mount brackets bolt up to the 3.2 block. The timing belt tensioner stud and pin must be transferred from a 3.0 block - the proper holes are present in the 3.2 block.
Next: I will finish the accessory end of the motor, install cam pulleys, timing belt, timing covers, and accessory belt drives. All will be from a 3.0 MTX motor except cam pulleys - 3.0 and 3.2 are identical. I will not be pulling the front head to compare combustion chamber design and volumes between 3.2 and 3.0 heads, as there seems to be no need to use the 3.0 heads. Also need to check if different 3.2 coil mounting bracket will work OK in MTX car, if not will have to drill and tap a couple more holes in the front head.
More info on swapping a factory 3.2 motor into a MTX SHO:
It appears possible to just use the 3.2 coil/bracket on the 3.2 long block in an MTX car, I don't think the angled mounting of the 3.2 coil/bracket will interfere with anything. Will require use of the 3.2 plug wires:
The following 3.0 parts were used: oil pan, oil pump, timing belt tensioner pulley, stud and pin, water pump/pulley, crank pulley, timing cover set, idler pulleys and brackets, PS pump/rear motor mount bracket, alternator/ac compressor/front motor mount bracket, and alternator. Only the front 3.2 head required a modification (as detailed in previous post) to allow proper fit of the 3.0 alternator and bolting the engine lift bracket to the head. Everything else bolted on with no modifications.
I am now 99.999% sure this 3.2 motor swap into a MTX car will work I will be 100% when it is installed and running. Still need to order a new 3.0 oil pump, stage 1 or 2 cams and install everything... it will be a while yet.
The only question remaining is... who said the factory 3.2/MTX combo won't work??
Correction: I am now 100% sure the swap works as the 3.2 has been up and running in a 90 mtx for about a year with no problems... so was it worth it ? YES!!! I have five SHOs and this one feels the most powerful for street driving. The extra low end torque is what this car needs. I did install stage II cams and now a Performance plus Y-pipe and Dynomax cat-back. Yet to be installed is a LPM/80mm MAF/extrude honed intake runners/big bore butterflies/68mm throttle body/SHO shop can.... even with the stock intake setup this thing screams!