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.

Ryan