Lets talk timing..
 

How did you figure out your low to mid timing tables? WOT timing is pretty easy to figure out, but how did you come up with the part throttle stuff? Most tuning seems like a dark art when it comes to questions so I thought I would try.

Me, I just add a few to the existing curve, but really dont know how far to push it unless you hook up to that special dyno that can hold cells.

I always try to bump them up till I see some kr then come back down a degree or two.

From HP Tuners forum: Here is the thread:
http://www.hptuners.com/forum/showthread.php?t=33447

You might be losing power by advancing without dyno testing, and not be anywhere near KR.

When I say I add until I get Kr, I mean under high map, low rpm situations. I don't add like 6 or 8degrees lol. Most of the time, i end up adding 2-3* in the cruise cells. I normally dont see more than +1 or 2 on mild load cells. Tuning part throttle is quite similar to wot, more isn't always better. I also try and feel how much throttle effort it takes to move/accelerate, when the timing is right, it requires less tps in the mid to upper loads. Gm does quite well on some vehicles, some are pretty soft too.

This seems very crude to me. Adding timing to the point of knock retard just means the engine is not liking it. Your ideal part throttle timing is when your manifold vacuum is the highest and your injector pulse width is the lowest. Also at this point your exhaust will become very quiet even if its got minimal sound control and that is because the spark timing is so in "tune" that the combustion event is occurring and completing before the exhaust valve opens. Its really not a science but its also something not a lot of people can ever get right either because its so touchy. My old 95 seems to like 46-47 degrees if timing and gets into the 48-52 kpa range at 2100 rpms (65 mph) and the pulse width generally stays under 2.00 gm/s but on the other hand the 99 likes way way less timing. I'm told the LSX head designs don't require as much timing nor can they handle as much timing as the older GEN 1 engines like. On it I want to say it sees around 30-33 degrees depending on the cell but on good flat ground it stays in the low to mid 50 kpa range at 1700 rpm at 65.

Yeah, the better the combustion chamber shape, the less timing it needs. Modern 4-valve heads need the least. Also, smaller bore size needs less timing. One guy on HP Tuners forum had a good idea: measure the point of maximum cylinder pressure with a pressure-sensing spark plug. I think something like 50° ATDC is the ideal point, at any rpm or kPa. You would just adjust advance at each point to get the peak to that point. Good idea, but too expensive to implement.

I honestly have not touched my part throttle timing ever. Just idle and wot. runs good.

I hardly ever mess with part throttle timing either, I usually just smooth it out so there aren't any huge transitions then make it look pretty, lol.

A vacuum gauge can be your best friend. It has been known to some people as a poor man's dyno. I don't know for certain about this, but I would assume you could tune for maximum vacuum and also achieve excellent fuel economy and power. I know backing just off of KR isn't always the best. A ping or KR is the harmonic vibration in the connecting rod caused by ignition before top dead center. In some situations this could be perfect, but not in all situations. Different octanes explode at different rates, and may not be effective for the best power or economy. Many people have actually made more power by reducing the octane for their application. I would describe a lower octane fuel as a fuel that not only ingites at a lower temperature, but a fuel that also expands at a slower rate. I would describe it sort of like black powder (lower octane fuel) vs gun powder (higher octane fuel). If you were trying to shoot a cannon ball, the gun powder would expand too fast, and not shoot the ball as far. I would also describe this like punching a baseball as opposed to throwing a baseball. You could punch the baseball with more force than throwing it, but the slower movement of throwing it will result in it traveling farther. Don't know if that makes sense, but I have had a long night tonight. Lol

I have a hard time making sense of this. The majority of my engines run time is spent at part throttle, usually about 2100 rpms going down the highway. Thats like someone posted on here in a shift points thread saying the stock part throttle shifts are really pretty good and just left them alone. That was my biggest complaint and what I spent the most time on with both trucks. You can take a 270 horse 5.3 and make it feel pretty strong if you shift it right.

Gadgetized, not a bad way of putting it.

Another way of looking at it is over timing an engine is like a vacuum cleaner with a plugged up bag. You can reach a point where you may not get spark knock but the combustion event is starting too soon and its actually pushing back down on the piston as its trying to come back up on the compression stroke.