Any feel like having a tuning discussion?

[ChevyHighPerformance]

Originally Posted by ChevyHighPerformance

My opinion only -> There are two major "flaws" in the stock PCM programming. One effects long-term engine durability and the other "flaw" I have never seen before in any other programs and makes even less sense to do this on the H3. The one flaw doesn't exist in the Colorado I5 tune which makes this confusing.

OK, the first item is the AC. The scenario is that you are trying to accelerate quickly onto a highway and the AC is on. On the vettes, f-bodies, etc. the AC will kick out above a certain RPM and throttle position. We all know the H3 doesn't have excess power but the AC never kicks off. Even though the AC takes a few HP when cruising it robs a bunch more at high RPMs. So I think the AC should kick off above perhaps 60% throttle and maybe 4000 - 4500 RPMs to reduce engine drag to get you accelerated quicker and I think would reduce wear on the AC compressor (maybe not the clutch though). When you drop below these setting the AC re-engages. During the 5 - 10 seconds while the AC is off, I don't think the cabin is going to get that hot so your balls stick to your leg. Every pro tuner I talked to agreed with this and doesn something similar for their tunes.

The other item needs some background. The engine operates in many modes but the two of issue is part throttle and WOT (wide open throttle). During part throttle, the PCM monitors the pre-cat O2 sensor and effectively adjusts the injector pulse width to maintain a 14.7:1 A/F ratio. The 14.7:1 A/F results in the lowest overall emissions and good fuel economy (best fuel economy is at about 15:1 A/F). During WOT or power enrichment, the PCM richens the A/F, provides more timing, and uses different auto tranny shift points for more power and maximum acceleration.

The boundary between these two mode is based on the throttle position. The vettes, f-bodies, I5 colorado/canyon, etc. enter WOT above 80% throttle. The H3 enters WOT above 94% throttle. I can see how minimizing undesired excursions into WOT will help fuel economy. The other issue is that running the engine pretty much flat out (93.9 % throttle) at such a lean A/F. I talked to several pro tuners about this and there was not unified position. One tuner gave an example (keep in mind the A/F for max power is about 13.1:1) that you could tune WOT for 13.1: and you'd make great power but the life of the engine is going to be reduced and 14.7 at essentially WOT is going in the wrong direction - so this tuner keeps the the WOT A/F to about 12.8ish and bumps up when you enter WOT (lower throttle position). Another tuner said that with the stock programming when you go to WOT the PCM delays several seconds already (so you are running at 14.7:1 at WOT) before power enrichment starts anyway. I don't know who is truly correct. I guess it depends on how you drive. For example, if I told you to press on the throttle and tell me what percentage you are at (0 - 100%) you might say 40% when you are actually at 70%. I am going to log some data and see what %throttle normally drive at and what peaks I hit when I don't want to goto WOT. I'll then set the WOT entry to be above the maximum I use when I drive.