'85 Saab 900 Turbo - Complete Rework! [Archive] - SaabCentral Forums

: '85 Saab 900 Turbo - Complete Rework!

5th May 2010, 12:17 AM
Since I've pretty much wrapped up my '86 8v N/A to Turbo conversion project, I figured it was time to start another. It's a 1985 Saab 900 Turbo, pretty much fully loaded aside from the 5-speed (which is of course preferred anyways). The car was given to my by the previous and original owner since '85 for free, but it had a bad transmission as the catch. It's pretty much completely rust free, was in an accident at some point but was properly repaired with full factory metal to the factory welds, and is otherwise free of dents. The color is currently Slate Blue Metallic (more of a dark grey) with Sierra (tan) leather interior. I'll be making the car somewhat of an SPG clone, but definitely more to my taste than the actual '85 SPG specs. The exterior will be black, perhaps with the earlier black SPG panels while the interior will be Buffalo Grey. Engine will be non-stock with T5 engine management, but I'm not going for super high performance.

I also have an '86 flatnose turbo convertible project continuing, but it will be more of a long term project. Much of what I do and learn in THIS project will be applied (hopefully perfected) to the 'vert project, so in a way they are linked. Since weather is still a bit on the unpredictable side in the Pacific Northwest right now, I'll be starting with the engine/transmission. Both will be rebuilt from the ground up, with a mix of used parts and new parts. Longevity will be a priority, but budget is, as always, tight.

First thing is building the bottom end. So far, I've torn the engine down, cleaned up the block, painted the block and honed the cylinders which were within spec (minimal wear). The car had somewhat low miles and it generally shows in he engine. I've mounted main and big end bearings, checked the clearances with Plastigage and everything is good (all well less than .002"). I still have yet to check rings and end float of the crank, at which point I'll start assembly.

I've decided to use '95 900 turbo 2.0L pistons in place of the original '85's. The '95 design seems superior, provides a little more compression (to counter the compression loss when I install the 2.1L head), and measures out withing .001"-.002" to the '85, so within what I think are reasonable tolerances. Following are some photos comparing the two.

Showing the difference in the top dishing. I'll be measuring the actual volume later, but it appears that the '95 is slightly less dished out (more obvious when looking in person):

Notice the 2 additional oiler holes at the gudgeon pin. The rod in the photo is the '85 rod, which also has an oiler hole at the top/gudgeon pin. The '95 rod is longer and did not have an oiler at the gudgeon.

Showing the differences in design. The oil passage seems to be a more modern design concept and worth the upgrade. I'm not sure how much difference it makes in practice though:

5th May 2010, 12:28 AM
Nice project! I had a question about those 95 pistons. Will you have to do any modifications to fit them in the block, or do they just snuggle with enough clearance for them to work without mods?

5th May 2010, 01:38 AM
Nice project! I had a question about those 95 pistons. Will you have to do any modifications to fit them in the block, or do they just snuggle with enough clearance for them to work without mods?
Depends a bit on a case by case basis. In my case, they are within specs for my block's factory bore. My '85 set is an "Standard AB" set, which is the second smallest. The measurement of the set I found would put them as a "Standard AB" as well (though I don't know if they named them that way in '95), so it was basically a perfect match. If you had a "Standard A" set with higher miles, the wear to the cylinder would probably bring it to the "Standard AB" tolerance. If you have a "Standard B" or larger set, the pistons I have would be too small. Whether or not they make larger standard sets for the '95, I don't really know. IF the pistons match, measured across the bottom perpendicular to the gudgeon, then they appear to be drop in. Of course, you do need to install the older rods since the ng900 has longer rods. The distance from the piston top to the center of the gudgeon is the same though, so one installed to the older rods the assembly is a match.

One thing I found is that the gudgeon is unworn on the '95 where the rod attaches, most likely due to the lack of oil at the rod causing the gudgeon to pivot at the ends where the oilers are in the piston. This is the opposite of the older design, where the rod wears the middle of the gudgeon and the end do not exhibit wear. As such, it can be a snug fit (almost like new), but is the proper diameter/same specs for both. The gudgeon from the '95 must be used, as it's a shorter length and the '85 gudgeon will not fit between the retainers.

21st May 2010, 01:33 AM
I had a good week of finding misc. parts for this project. I pulled a DI cassette from a '94-'95 9000 Aero along with the T5 ECU. Earlier in the month I had picked up the wiring harness and all the sensors (and crank wheel) from the '95 turbo I pulled the pistons from. At this point, I believe I have a complete setup for T5. :D

I also found a set of SPG rims from a '91 on CL. The price was right, but they will require a lot of work. The previous owner (not the current owner I bought them from) had the wheels and caps chromed. Not painted chrome, but actually chrome plated. They are frankly hideous. :O Since I plan to convert the brake system to the later '88/'89 style, I'll be needing a set of rims with the later bolt pattern and at $80 these fit the bill, albeit with a great deal of elbow grease required. I'll post some photos of them later, they'll make for a good laugh.