Quote:
Originally Posted by v8volvo
I was going to ask what you were planning to do about gearing, but then I didn't because I think you're right, the gasser gearing will probably be fine as is. These old IDI motors like to rev and there are seemingly no downsides to letting them do it. In the example of the Volvos, the diesel models use exactly the same transmission and rear axle gearing from the factory as most of the equivalent gas models. In fact the diesels are actually geared shorter than some of the NA gassers. The engines are suited by design for fairly high engine speeds, small lightweight pistons, direct acting OHC valvetrain, etc, it was clearly part of the plan for them. Especially true for the original design "short stroke" family like the D24/T and your "D20T" (the 1.5/1.6 4cyl, 2.0 5cyl, 2.4 6cyl). The raised deck generation IDI and TDI motors (1.9/2.0 4cyl and 2.4/2.5 5cyl) with longer strokes are maybe a little less optimized for it.
Anyway if the gas engine is turning 3200 at 70 that seems like it would be just fine with the diesel. My '83 760 D24T with stock size tires and stock gearing turns about 3400 rpm in overdrive at 85mph, which is still too slow to keep up with highway traffic here. But it seems happy to do those revs or more all day, in fact it seems to be capable of quite a bit more, although with the 1983-only 85mph speedo I am not too tempted to explore.  Really the ability to rev smoothly and provide a wide power band is one of the neat features of the old IDI turbo engines, and makes them fun to use for hard driving. The later direct injection engines are much more limited on the top end, although their low end response is better. They seem to pretty much run out of breath even before 4000 rpm. |
My 1.6 doesn't really generate good power until around 3000rpm's. When I owned the D24T Volvo I recall it had good power below 3000 but didn't mind running at 3500 either. TDI's are better between 2000 and 3000. I think it will be fine which is why, 9 years later, I'm continuing with the project.
I did a compression test before dismantling all the exterior bits today and it was pretty sad, around 280 psi average, but the engine has been sitting a long time. It did hold pressure so I think it will be ok. There was one potentially major problem, the #4 injector was burned up on the tip, I think the crush washer wasn't seated properly by the PO and it wasn't emitting diesel, so that cylinder was running dry for I don't know how long. It only had 50psi dry, but when I put oil in the cylinder it went up to 220.
I'll be taking the head off tomorrow and see what's up. Stay tuned.