Bad tune, or engine at its limit?

[90Vette]

What do you mean that it shows up in green? I'm guessing that's specific to the datalogging software you use?

Weird, I'd heard that KR could absolutely cripple a pass. Were you ever seeing the full 5°?

Interesting to use a less rich AFR to hedge against the affects of changing DA. Although (assuming you're racing at the same elevation) aren't there MAT tables you could tune to have the same effect?

I'll give that a shot next time I hit the strip. It's a bit tricky to dial in a specific shift point with my tach being off though. I'll have to do a couple pulls with someone watching the datalogger to figure out what my tach reads at 5500 RPM. It's probably gonna be a while till I can make it out though - hardly have time to breathe when I'm in school.

I've toyed around with the idea of calculating a dyno curve from my datalogs, but I haven't had much luck with that. EDIT: Gave it another shot, and with a lot of smoothing I got something that is questionably reliable and marginally useful:
Dyno Chart.png
(Not sure what's happening with the axis labels when I copy as an image, but HP is on the left and TQ on the right).
It doesn't take drag into account, it's still pretty noisy, and it's rating my power at substantially less than my trap speed indicates, but it looks like it should still be pulling at 5k. I'll give it another go with another dataset and see what I get. If I have time, I'll try some sort of complementary filter to combine my different data sources (tach, speedo, and accelerometer).

Here's another. This one looks a lot cleaner (lower speed pull) and it shows HP dipping after mid-4k.
Dyno 2.png

[Dirtybob]

What do you mean that it shows up in green? I'm guessing that's specific to the datalogging software you use?
Weird, I'd heard that KR could absolutely cripple a pass. Were you ever seeing the full 5°?

using eehack analysis function.
I did see the full 5 deg. of KR but I had the timing up to 35+ at that point running it on 93 octane. Timeslip differences were so small that it just looked like typical pass to pass variations. Your mileage may vary.

Interesting to use a less rich AFR to hedge against the affects of changing DA. Although (assuming you're racing at the same elevation) aren't there MAT tables you could tune to have the same effect?

I haven't had much opportunity to test how well that works but that is how I would tune a carb. We got real busy at work and I have been chasing some weird intermittent heak soaked electrical issue (no CEL, nothing I can see on the logs...). I've fixed several problems with connectors/wiring and replaced a few old sensors but the car will still act up once or twice a month. If I start going rounds it is guaranteed to act up before semi finals (murphy).
Not too sure that the 8051 pcm uses MAT. Initially I was tweaking MAF and timing tables but my MAF was going bad. After replacing the MAF I copied in a stock table then logged it and it was almost spot on, just a wee bit lean cruising. Went back through and got PE to between 13.1/13.4, raised shift points ~100 rpm and left it alone.
I also used a piston stop and fabbed a timing pointer, discovered that 3 different (not AC Delco) optis will give 3 different readings on the same tune. The car had some cheap opti on it when I bought it.
Have yet to find anyone willing to sit on the bumper with a timing light while I run it through 1st and 2nd to see what it looks like with a load on it. At this point an opti change merits a bunch of logging at the very least and probably a new timing curve.
Hard to understand why some people hate the LT1.

If your [Dyno 2] graph is accurate, I would try shifting at 4500/4750 rpm. The question is why in the blank would your motor be laying over that early?
Are you getting enough fuel or does it go lean up top?
I put a cheap tach in mine but only use it on the starting line for launch rpm. People sometimes ask me why my redline is set at 1500 rpm...

[90Vette]

Gotta love those intermittent electrical problems. Had one for a while that would randomly make my engine cut out, which was especially fun when accelerating hard as I'd go from full accel to full engine braking back to full accel when the engine restarted.

Man, I really don't want that to be my shift point. I did another graph and found a similar peak though. Granted, I'm not accounting for drag, so these graphs underestimate the peak a little bit. But still. Only thing I can think is the cam. Looking at my fuel tables, volumetric efficiency starts to drop pretty fast past 4400. I haven't been able to hook up a FP gauge yet, but according to my passenger the wideband was holding steady without any spike at the top end, which I think would mean I'm getting enough fuel.

Dyno 3 (53-90mph).png

[Dirtybob]

are you confident that the valves are set correctly?
do you own a vacuum gauge? IMHO they should be standard equipment installed at the factory.

http://www.tuneruniversity.com/blog/...-vacuum-gauge/

[90Vette]

Yep, I think I did around 1/2 turn of preload.

No, but my car is speed-density, so it has a MAP sensor. You can see the readings in the datalog I attached to my original post.

[Dirtybob]

My car also has a MAP sensor but I have trust issues when it comes to the electronic bits on old cars...

[90Vette]

It seems like my MAP sensor is functioning correctly - shows 30-40 kPa at idle, which drops to 10ish on decel, and rises to atmospheric pressure on acceleration.