View Full Version : VVT Tuning

October 17th, 2007, 02:45 PM
Well, after hours of reading up on the VVT system and the whole cam phasing process on our 4.2's, I have decided to finally take a stab at trying to mess with mine. I have always noticed a bit of KR with my Trailblazer (2005) even with just stock timing tables on 93 octane.

After my readings, which I may be completley wrong on this, I believe that the VVT is causing the KR due to the fact that it is also doubles as an EGR system. The more the cam is retarded, the more exhaust is entering back in through the intake valve, heating up the intake charge.

At Idle the cam angle is 0 which is fully advanced, and then from there it moves around based on several paramaters. Now in PE mode, from 2800 to 5200 the cam angle is 12* for that whole range, that seems pretty generic to me. I don't fully understand the whole vvt sytem completely but it seems that within a 2400 rpm range, that there would be different angles at the different rpm ranges. That makes me believe that GM may have this table set more for emissions purposes than power purposes.

So with my limited access to a dyno here in my area, I am going to try to use the EFILive hp estimator to help me make some changes. I do believe the cam angles will need to retard as rpms rise, I do not believe that they should be retarding as much as they are from the factory. Hopefully within a week or two I will have some results to post.

Hopefully I am somewhat correct in my thoughts of all this and if you guys have any info to add, that would be awesome. Erik and Blandmiller, you guys jump in here and let me know some of your thoughts.


October 17th, 2007, 05:07 PM
I really havent messed around with mine, just advanced it a little above 2400rpm. Havent flashed the stock parameters in a while, and with me being in Spokane and my TB in Seattle at my parent's, Im not much help right now. I need to talk to the people here at school that have I6 TBs, there are a bunch of them but all older than I am.

I just compared my stock 02 VVT params to the 03 Voy that is in the Bins folder and see some changes, maybe thats how GM grabbed the extra hp from the 03-05s over the 02s...(270 vs 275). I will try them when I go home, unfortunately that wont be until Xmas (but my parents are bringing my TB out here this weekend, maybe I can try some things then).

Thanks for any and all input on this man, I think there is some power potential hidden away in there that we can unlock somehow.

October 22nd, 2007, 11:48 AM
Well, I have had a little time to see if I could coax any more power without the use of a dyno, and to be honest I advanced (lowered the values in the table), retarded (raised the vaues), and even ran the stock settings. Using the HP estimator in the scan tool (which I know is not very accurate) I figured I could get consistant enough results to see what was what with the cam phasing.
Here are my results:
Advanced made a bit more power down low and in the midrange. However, too much advance and it started losing power.
Retarding the cam made it lose power down low and in the mid range.
Stock cam table
My table I am currently running:
I actually only saw very minimal change for the range of changes I made. My modified table I am currently running yielded a little more low end and mid-range with basically no change in top end power.
Here are the logs from the stock cam phasing and modified cam tunes. I hi-lighted the same basic area in both logs so you can see the "average power" from 2500 to 6200 rpms. I shift at 6500 or so, but peak power was at 6200. It started falling off after that, but It makes a lot more power at 6300-6500 than if it shifted at 6200, because the rpms don't drop as much after the shift.
It does feel a little better in the mid-range with the modified table so I will roll with it.
Moving on to my (and many other's) Knock retard issues. I run 93 octane on the stock PE timing tables and I was getting up to 5-6* of KR at WOT. I put wideband sensor in today and found that the stock PE settings have the fueling start of at about 13.2 at low rpms and it tapered down to about 12.5 in the upper rpms. I was getting knock down low and in the midrange because it was too lean, I set the PE modifier table up where my fueling starts at 12.5ish and tapers up to 13.0 in the upper rpms. That took care of my KR issues. The max I had was .8 deg in the midrange and 0 everywhere else. I can live with that. Here is a screenshot from the log showing some AFR and spark data:
Then during that run at about 4800 rpms in second gear, the AFR went rich, like 11.7 rich and I knew what it was....Cat Converter Protection mode. EFILive currently does not have that table in the current calibration file, so I can't fix that yet, but hopefully soon, that will be taken care of. Here is a screenshot of the cat protection at work:
I can probably run a little more timing in the upper rpms, but I wanted to test all this with as little changes as possible to hopefully see some results. I think if we had VVT on the intake, it would yield some better gains, and also It would definetly be better to tune this on a dyno, I just don't have access to one.
Maybe this will help some of you guys out and shed some light on some things that might have been previously confusing.
Thanks, Ryan

October 22nd, 2007, 03:13 PM
Very nice man, thanks for the info. I will definitely advance (lower values) of the VVT table for my next round of tuning when I go home to my TB over xmas. I really hope Jesse is working on a COT parameter so we can turn it off. I can feel it when the engine gets hot and it kicks in, becomes a dog. What are you running in your PE AFR tables?

October 23rd, 2007, 01:14 PM
Eirk, my current PE tables are as follows:

PE vs. ECT
LABELS P.E AFR Based on CTS (Air/Fuel Ratio)
ECT °F Value
-31 12.000000
-13 12.000000
5 12.000000
14 12.000000
23 12.000000
32 12.000000
41 12.000000
68 12.000000
95 12.000000
131 12.500000
176 12.600000
221 12.600000
284 12.600000

And my Modifier table is:
LABELS P.E AFR RPM Multiplier (Factor)
RPM Value
1200 0.968750
1600 0.968750
2000 0.968750
2400 0.968750
2800 0.968750
3200 0.968750
3600 0.976563
4000 0.992188
4400 1.000000
4800 1.000000
5200 1.000000
5600 1.000000
6000 0.984375
6400 0.984375

October 23rd, 2007, 05:06 PM
Thanks man, thats about what mine are at now. Im commanding 12.5 at the normal OT but commanding more like a 12.0 (using the PE multi) from 3200-4800rpm. It likes the extra fuel, seems to pull harder but I havent logged it a lot with this tune. When I get home I will look into it more.

October 24th, 2007, 02:32 AM
I can't say much about a TB .tun , but I set PE at 1.15 EQ or 12.78 AFR all values and runs great with that setting . My experience is 12.8 to 13.0 produces the best SOTP feel .
I do have a 06 and have limited tables .

October 24th, 2007, 10:43 AM
I agree with TunedbyGM, 12.8-13 makes more power.

October 24th, 2007, 11:34 AM
Yeah, it does. I had to fatten u the mixture below 4500 rpms or so to help with the knock.

October 24th, 2007, 12:02 PM
I will try 12.8-13 when I get a chance to flash my TB.