Isn't the rule of thumb: 2nd gear VS 3rd gear is usually worth +/- 20 rwhp?

That wasn't the case yesterday. Had some other f#@kery going on too. Possibly the converter didn't like being locked. And absolutely ZERO of my data logs saved. So I have nothing to review and help me figure out why it did what it did yesterday. Live data yesterday, no knock and it was a hair rich.

 

say huh?
while i get your basic gist, there ain't much context to go off of... and 7-8% margin seems like a lot of wiggle room if you're trying to tune based on this guestimate.


the HP difference depends on how high you rev it because higher rpm makes a bigger difference in the HP number. you mentioned the torque converter may or may not've locked up: that'll make a difference, too, because being unlocked has the same effect as slipping the clutch or spinning the tires while trying to measure rotational resistance - it'll skew your results. the 2nd vs 3rd difference would also depend on what diff gears & tire size (final drive ratio) you're running because a high final drive will rob more torque than a low ratio.

 

Basic run down is: 2000 GMC Sierra RCSB: LQ4, 80E, Comp XR275 cam, longtubes, an exhaust system I built - dual 2.5, single 3.5" exit, TBSS intake, 92mm TB, Walbro 255lph, Gen IV 5.3L FF injectors, CAI, tuned on 93 pump, FL performance tq converters 3200 stall, 3.73s, 265/50r17s (29.5" tall)

When it was originally tuned in 2020, we dyno'd it in 2nd gear - stock driveshaft problems. And I was getting some valve float above 5500. Since then I put an aftermarket driveshaft in it and changed the valvesprings. Yesterday was basically to see if it had any valve float and what it would pick up run in 3rd VS 2nd. The TQ picked up - HP was nearly identical. 1st pull was smooth, no issues. 2nd and 3rd pulls, it bogged down and sounded very unhappy. The only difference between the 1st pull and the last 2 was that I opened the cut outs VS running through the big case Magnaflow. The only caveat is that at least the valve float appears to be gone. I should have made at least one pull in 3rd without the converter locked to see if anything changed. I will likely do a few short pulls on the street ASAP to see what it does. Hopefully HP Tuners will grab and save a data log. It usually auto saves, not sure what its deal was yesterday.

 

UPDATE - did a few pulls on the street. It HATES the cut outs being open. Problem solved for now, not going to worry about the cut outs.

 

Do you have a wideband installed? Open cutouts skewing the tune could suggest undersized exhaust, or the cutout placement is too close to the 02 sensor.

 

No wideband, cut outs are a few feet downstream from the 02s

In other news, the lockup clutch in the converter is cooked.