VERY disappointing night at the track with my new 3.42 gears (C6/A6 Corvette)

[thesubfloor]

I have an 07 C6 Corvette with an A6 and as of last Saturday, newly installed 3.42 gears.

The car has several mods (cam, headers, CAI, 3000 stall) and my best time on a Wednesday night is 11.56 @ 122mph.

Using the tune from the 11.56 run, I changed only the gear ratio and let it do an Auto Scale of the transmission tables. So far so good, right? Nope, the best I could manage was 11.73 which was disappointing since I and several other people thought it would actually run a little quicker.

I'm not ready to blame the gears just yet because I noticed some weirdness in the logs from last night. Specifically:

1) The car refused to shift into second gear until it was past 7000 rpm. No matter how low I set it in the tune, it simply wouldn't shift when I told it. The only reason I didn't hit the rev-limiter is that I have it set to 7200. I know that I'm able to change the other shift points correctly because earlier in the evening the car surprised me by shifting into 5th right at the traps. When I changed that and ran the next time it stayed in 4th the whole time.

2) In some of my previous runs before last night, I noticed that the Injector Duty seemed to stay pretty much in sync with the RPM. If you look at the scan from last night however, that wasn't the case. Could this have anything to do with the car shifting way too late?

3) During the race my spark advance seemed somewhat erratic in the log. I checked this against prior runs and it's usually pretty flat which is why I thought it looked odd.

4) Is the 4.9 degrees of KR at launch normal?


Also, after changing the gears did I need to do anything more than simply changing the gear ratio in the tune?

Any thoughts or suggestions would be appreciated.

Thanks,
Christopher

P.S. I had the car tuned by someone in Chicago and just tweak it myself when I'm at the track.

[BBA]

Sounds like you need to change a few more settings for revs per mile and such.

The PCM now thinks you are making more torque because of the quicker gearing, so it's limiting by TM unless you have already removed some limiting in the max torque per gear settings.

The engine TM will play havoc on spark timing.

KR on launch is not normal. You sure you have good gas in it and have you increased your base/high/lo timing tables? If so, your operating in a different airflow region because of engine rev up quicker under load. You will want to do some KR logging and modificatino of timing tables to get rid of it.

Also reduce Burst KR settings, the PCM now thinks your accellerating quicker and calculates more reduction for burst knock reduction.

[thesubfloor]

I really appreciate your reply, thanks.

For the late 1-2 shift, the theory that I got from the tuner for RPM Transmssions (which was supported by my own research on this forum) is this:

With the combination of a looser converter along with the different gears, the engine RPMs rise too fast for the PCM to keep up. While I was at the track I thought that lowering the RPM to 6200 would work but he suggested going even lower. He mentioned one of his customers has a turbo and he had to set his to 4000 RPM to avoid hitting the 7200 RPM rev-limiter. That sounds plausible so I'm going to try it tomorrow night.

I've got all the TM turned off and with the exception of the KR I get at launch, it doesn't seem to appear anywhere else.

I'm still pretty new at this and from what I know, only the High and Low Octane tables were changed for the Main Spark Advance. I'm not sure where and how to reduce the burst KR settings so I'd appreciate any tips on how to do that, as well as the other timing table adjustments that you think might help me out.

How much do you think that KR spike is hurting my ET?

Christopher

[BBA]

Haven't had a chance to really dive into it yet but was curious if you figured anything out?

[thesubfloor]

Yes, and thanks for checking in.

I went to the track again on Friday night and by setting my 1-2 shift point to 5200 I was able to have it consistently shift between 6600 and 6800 in my 8 runs that night.

I attached two scans and as you can see from them I also managed to get my Spark Advance to hold steady during the run.

The only problem I have left is the Spark Advance taking a nosedive during my launch. I was able to determine that it was actual knock and not burst, but the funny thing was that it didn't happen all the time.

After I got home that night I plotted the histogram points to determine where exactly I needed to bump up the timing, but only had mixed results in that it worked well a couple of times whereas other times I was still getting knock when I tried a simulated launch.

In that time interval between when I first punch the throttle and when the Calc CylAir settles down to normal values, what's the best way to dial in my Spark Advance? Do I also possibly need to change something with my fuel so that the quick influx of additional air doesn't cause the knock in the first place?

Thanks again for all your help,
Christopher

[BBA]

Judging by the first scan log (havent looked at your new one yet) I would take 3 degrees out in the cells just before where the KR happens and smooth the values for the cells adjacent and where it is in before the KR decays. (I like to go half the amount KR reduces by, seems to work well since KR seems to remove twice what it needs to).

The shift speeds can be brought into line easier by adjusting max trans pressure up. Of course it may just be my older version of HPT but I do not see the force motor current tables in your trans controller. If you can see the tables, move the values for 89, 91 and 93 kPa down in value where the shift is (set the 93 kPa table to about 8 or 10).

If your version does not have the force motor current tables either, then you can always adjust max pressure manually, by removing the trans pan and adjusting the pressure regulator solenoid pre-tension set screw in by about 1/4 turn. (thats messy but easy).

[thesubfloor]

I played with the Spark Advance tables so hopefully it'll be better tonight.

I don't have very much control with the transmission settings but as I mentioned in my last post, what did work was lowering my 1-2 shift point to 5000.

Thanks,
Christopher

[RWTD]

Yes, and thanks for checking in.

I went to the track again on Friday night and by setting my 1-2 shift point to 5200 I was able to have it consistently shift between 6600 and 6800 in my 8 runs that night.

Christopher, not to sound harsh, but that's really a "bandaid" approach. You should keep the Shift Point RPM where you want it to shift, and instead change the Shift Point MPH so that the Commanded Shit RPM becomes the Actual Shift RPM. If you will, go out and try it out some on the street and see if you can't get it right this way. It'll make it much easier for you in the future.

[thesubfloor]

Christopher, not to sound harsh, but that's really a "bandaid" approach. You should keep the Shift Point RPM where you want it to shift, and instead change the Shift Point MPH so that the Commanded Shit RPM becomes the Actual Shift RPM. If you will, go out and try it out some on the street and see if you can't get it right this way. It'll make it much easier for you in the future.

Thanks, but I already tried that and the suggestion of lowering the shift points was given to me by the tuner for RPM Transmissions. Here's the blurb that he sent me:

Originally Posted by RoadRebel
You need to lower the WOT shift MPH and RPMs. When the 3.42 gear go in things happen so fast the PCM can not keep up. All you need to do is give it some additional lead on the 1-2 shift.

I'm guessing that you already know this, but just because you tell the PCM that you want the car to shift at a certain RPM/MPH setting does not guarantee that it will happen then. This as it turns out is not a unique thing with Corvettes as I scanned a Camaro Z28 on Friday night and even though her shift points were set at 6400, the car didn't shift at until after 6600 RPM.

[RWTD]

The reason it's off is because the Shift Point MPH is off. If you would set the RPM where you want it, then adjust the Shift Point MPH until the Commanded RPM becomes Actual. Here's a quick search with a little more info:

http://www.hptuners.com/forum/showth...5295#post25295

See post #2 and #4.

And, trust me, the pcm is much faster than you think. It can easily command that shift on time, even with the change in gears. You can log trans status to see exactly when it's commanding the shift.

I tune for these setups all the time, without issue. It's possible you're only adjusting 1 of the many tables that should be modified, and/or not adjusting them properly. Now, with that being said, pressures can play a big role in shifting performance, as well, as you also know, so it is possible that the shift is being commanded on time, but the trans is "rolling" through the shift, thus necessitating an earlier "command" point, resulting in a shift, but obviously a loss of performance, however slight.

[thesubfloor]

Take a look at my tune and scan in the first post of this thread. The actual 1-2 shift didn't happen until 7114 RPM even though the trans commanded it at the correct time.

I know exactly what you're saying but the reality is that what's supposed to happen and what does happen can be (and quite often are) two totally separate things especially at the track.

The other thing is that with the A6 transmission, the only control that I have over shift pressures is the maximum values unlike the A4 which allows for much more control.

[BBA]

I've seen it before on Trailblazers with mods such as stall and cam.

I think your shift pressure is too low to hold through the power level you have and the engine is spinning through to higher RPMs, that and because of the hydraulic shift timings. You will likely have to do some trans work such as bumping the pressure set screw on the solenoid or installing a shift kit since you do not have the force motor current tables in your HPT GUI (Chris, why is it missing for 6 speed auto's?)

[EC_Tune]

The six speed is a completely different animal than the 4L60E & 4L80E since it is a clutch to clutch style instead of planet/sun style. It has 5 pressure regulators for the different clutch packs inside. Chris is in the process of adding around 400 new parameters to the 6 speed autos. Now things get really confusing eh?

The auto adjustment of the speedo doesn't always work well on the Gen IV applications so I created a spreadsheet that does work well. It's in the V8 Misc stickies if you are interested. You have to put in the correct data (start with stock to make sure things calc right first!) or the spreadsheet will spit out garbage.

[BBA]

well well...looks like 'thesubfloor' may be able to adjust shift pressures to get the high RPM shift firmed up a bit now with the beta stuff.

Give it a shot!!!

[thesubfloor]

I could, if my car wasn't at the dealership getting the transmission replaced.

Speaking of the new parameters, is there any documentation on how each one works? I also looked at the A6 walkthrough in Bill's thread but there wasn't really anything useful in it. Or did I miss something?