I've been fiddling around with timing for my mild cam LQ9 built. I built the engine from scratch (parts) and used a P01 computer from 5.3L LM7 engine I scrapped. I was able to with some hackery get the engine to run on the 5.3L tune from the older PCM. Then dialed in my VE and MAF tables.

However, power was pretty well, $hit. I started tuning the Spark Table using a pretty crude method of adding timing until I observed knock / computer removing where knock was and updating the table. I really really really don't like this. Called a powertrain engineer I know from back in the day. He said there should be an idea timing advance of TDC based off of stroke to rod length (leverage on crank). Then several other factors ad onto that advance for fuel mixture, optimal cylinder pressure, head flow, etc. In short, really need an engine dyno and some other sensors to dial all that in. Not going to happen.

Long story short, I decided to pull a LQ9 tune. I took my VE and MAF tables and put them into a 2003 Silverado SS / LQ9 tune. I then made the High Octane Table match the Low Octane table. It works MUCH better. However, it's still pulling timing. Seems the camshaft effects timing? I'm really a novice on this.

My camshaft is a Roger Vinci grind #562. Intake 0.578/213 Exhaust 0.587/220 Overlap 114+4A. I get a bit more lift out of it as I'm using 2116LSR Johns Lifters. They short piston / pump design, so I get another 20 thousands or so lift over stock lifters (guessing).

With the LQ9 map it feels like I'm a tad low on power under 1500 RPM and after 2400 RPM I start to get a little knock (files attached). How should I attack, getting this timing dialed in so I have safe advance tables?

Note I used everything from Silverado SS tune except the Spark Retard Limit. It went really negative. Made me nervous of igniting too early, prior to TDC. Maybe this is an issue? I kept the more conservative LM7 config.


LM7 Table


LQ9 Table

 

A couple of things to be aware of. The timing retard limit is for after TDC. No worries about igniting early with that table. The other issue is that all of the GM truck tunes have been known for hitting knock retard even without actual knock present. I have not been HPT tuning in a while, so I would have to look up the table that causes this. Also, pretty much all gm tunes are going to hit some knock retard on a factory tune with just the high octane table values in play.

 

@gametech thanks for the help. So sounds like the computer has a safe guard in the software to limit timing to no less than 0 degrees, TDC? Just really shocked to see negative timing values in the configuration, even from factory.

 

I did not make my statement clear. The negative timing values will fire AFTER TDC. This would dramatically reduce power, as well as being bad on catalytic converters, but would present no danger of pre ignition. There are, however many other tables that affect timing, and if memory serves there is one that will give you an absolute minimum allowed timing. I am sorry to be so vague, but some computers have different tables than others, and I have not had occasion to use HPT in a couple of years. The only recent tuning I have done is S&S motorcycle tuning, which is an entirely different situation.
edit-- I just remembered the knock retard table I was thinking about. It is called burst knock, and it preemptively pulls timing in anticipation of possible knock. It is very aggressive in the truck tunes.