I took my truck to the new dyno shop here in Tulsa on Saturday and got some numbers with a non-plugged fuel filter. Peaked at 141 rwhp @ 3100 rpm and 263 ft-lbs. It really doesn't have a peak torque rpm, it made that from 1500-2700 rpm. It didn't drop below 250 ft-lbs until 2900 rpm. At first I was a little concerned with the numbers since they were lower than before, but then I remember I had to pull some timing last week because of the hot weather and pulling the boat. Duh, I should have reset it but forgot. Regardless, that's only about 4% lower than the previous numbers (145/272) which is well within the realm of experimental error anyway. It was a different dyno than I used before and it was about 18 degrees hotter and lower barometer than last time. The correction factor should compensate, but it isn't 100% accurate. This dyno also only had about 30 pulls on it when I did my two pulls, it might take some time to loosen up or something but any change from that should be negligible.

The air/fuel ratio really tells a story. If anyone dyno's their truck I highly recommend checking the a/f ratio if possible. On the first pull it started at about 15.5 and dropped rapidly to 13 by 1850 rpm and stayed there until 2100 rpm. At that point it dropped to 11.8 by 2250 and slowly climbed back up to 12.7 at 2900. From 2900-3000 it spiked to 14 and slowly tapered back down to 11.5 at 3500 where it stayed until I lifted a little past 3800. Ideally it would sit about ~13.5 all the way through the test. For those that are scratching their heads right now, 14.7 is the theoretical perfect ratio, ~13.5 typically produces peak power, lower numbers are rich, higher are lean. the a/f was unexpectedly rich for the first 2/3 of the test, then spiked to lean for a few hundred rpm, then got very rich at the top end. For the second run I pulled out 1/2 turn of fuel pressure, which resulted in a much more smooth and controlled fuel curve. It started at 15.5 just like before and dropped smoothly to 14 by 1800 rpm and stayed there until 2300 rpm. At 2300 it began to drop and hit 13 at 2400 where it pretty much stayed until 3000. At 3000 it began to drop and leveled off about 11.8 at 3450 where it stayed through 3800.

The moral of the story is that the seat of your pants is a lousy tuning tool. I think I mentioned this in a thread a while back and now it has bitten me in the butt. I've been chasing a lean condition above 3000 rpm for nearly 4 years that didn't exist. Proper testing is the only way to quantify results. The top end felt better when I added fuel because the power below 3000 was reduced, which made the drop above 3000 less pronounced. The top end richened up because the PCM was estimating airflow based on part throttle sensor readings. The airflow became limited by the valve timing and port flow, but more fuel was being added because the PCM can't tell how much air is flowing at WOT. What does all this mean? It means that at 3400 rpm there is about 13% more fuel than ideal. If I can add the appropriate amount of air I should gain a lot more power, maybe as much as 25. We'll see in the next few weeks when I hopefully get the 1.73 rockers installed.

 

Oh, if anybody is interested in having a dyno day I can arrange that. The dyno owner is a friend of mine and will cut us a deal. We probably need 10 trucks participating to make it worth while.

 

Where is the dyno located? I'd love to hit it with my truck..I'm hoping to get about 270-300ftlbs or torque to the wheels.

Edit...after seeing your numbers (that'sa what I get for skimming over the post) ..I'm hoping to ger over 300 now.

 

Tulsa's about a 2 day drive from Georgia, you can find a closer location here.