Well, the shop that originally dyno'd my car went belly-up a few weeks after my baseline runs, darnit. So, I had to find another dyno shop to re-do the baselines. The new place has a different DynoJet dyno... it's a larger, in-floor setup with heavier rollers, which are needed to properly load up high-power engines (i.e., 1000hp Duramax, PowerStroke, or Cummins).
I only got two good dyno pulls, there was a third run in the middle but the dyno lost tach signal so the data was useless. This is a common problem when there is not an electrical tach signal available... they use an optical sensor on the harmonic balancer, but the car & engine can move slightly when loaded, and the sensor loses signal momentarily. The two good runs were nearly identical though. The first run started at 70°C on the temp gauge, the final was 90-95°C, no big power difference though. Ambient was 70°F. The results were interesting, although a bit confusing:
Original dyno: approx 140hp (@ 4400 rpm) at the wheels, with 190lb-ft of torque (@
3100 rpm). Assuming a conservative 18% powertrain loss, that would be 170hp and 230lb-ft at the crank.
Current dyno: approx 130hp (@ 4500 rpm) at the wheels, with 245lb-ft of torque (@
2100 rpm). Assuming a conservative 18% powertrain loss, that would be 160hp and 300lb-ft at the crank (!!).
Now, to clarify the results a little... the original dyno didn't load the engine below 3100rpm. The graph started at ~3100rpm, and that's where the peak torque was, right at the beginning. The second dyno (with heavier rollers, etc) was able to load the engine as low as 2100rpm (probably the flash point of the torque converter), and on the second run, the torque peak was also at the beginning of the graph... it gradually declined all the way through the run. Interestingly, on the second dyno, the torque at 3100rpm was approx 185 lb-ft, very close to what the first dyno read at the same RPM.
Both runs went to the governor at 5400rpm. Power was flat at 125-130hp from almost 3800-4800rpm, which surprised me (yes, a flat HP curve, not a flat torque curve!) Power was good to 5200rpm but then it dopped sharply between 5200 and 5400 (went from approx 105hp @5200, down to approx 70hp @ 5400).
What I find strange is the very high torque reading. There's no way my car is putting out 300lb-ft at the crank. I assume it has to be the torque converter affecting the readings at those low RPMs. Also interesting is the power drop from the first dyno to the second. I dyno'd my gasser on the second dyno also, but it read HIGHER, not lower - so it's not necessarily that the second dyno reads lower. Anyway, mission accomplished, I now have a good baseline from the second dyno. The engine configuration was the same, IP is maxed out, stock boost, etc. It's possible the power drop was fuel related, my last couple of tanks from Flying J have netted MPG numbers below normal (in both my diesels), indicating lower BTU content... which could explain the slight power drop.
I attached a scan of the factory sales brochure from 1987, showing the stock power curve. The power peak should be at 4600rpm, and torque peak should be at 2400rpm (although the torque curve is flat at approx 200 lb-ft from 1900-3000 rpm).
