Unpredictable boost amount

[KartRacer]

I guess I still cannot wrap my head around the factory programming.
When I hit the throttle, I never know what I'm going to get. One time 14# boost next time 10, sometimes even less. I have tried to figure out how to repeat the situation to no avail. Cold, hot, uphill, downhill, curve, straight. Turn off traction control but still get the unpredictable results. Insights from someone in the know would be appreciated.
BTW, no check engine lights or faults shown according to Onstar.

Maybe it's always been this way but I don't think so. 49,000 on the odometer.
Perplexed.

 

[Stew]

The ECU isn't trying to hit a boost target, it's trying to hit a TQ target. If it can hit that target with 10 lbs of boost that's all you'll get. The amount of boost needed to hit a TQ target will vary depending on a lot of things, like inlet air temp, how much advance it can use, air density, etc.

If you're tuned though you can tune for a target boost amount rather than a target TQ amount if you want. The downside I guess is that some days you'll make more power than others.

 

[KartRacer]

Thanks stew
That is what I suspected but never got a direct answer. (At least one I understood)
Does a tune then shoot for safe torque value which then can generate more boost or is there other more important criteria to shoot for?
If the computer controls system to keep from overshooting torque then fuel no longer becomes a determining factor as the computer will not allow excess torque, correct?
Thanks!

 

[BNRacing]

Thanks stew
That is what I suspected but never got a direct answer. (At least one I understood)
Does a tune then shoot for safe torque value which then can generate more boost or is there other more important criteria to shoot for?
If the computer controls system to keep from overshooting torque then fuel no longer becomes a determining factor as the computer will not allow excess torque, correct?
Thanks!

That's one way of doing it. You can also ask for more power than the engine will ever be able to make, and then hard cap boost so it always makes that much peak. Lots of ways of doing it.

There's more to it than just that, with fueling tables, VVT, etc. though as well.

Here's a visual guide

 

[KartRacer]

That's one way of doing it. You can also ask for more power than the engine will ever be able to make, and then hard cap boost so it always makes that much peak. Lots of ways of doing it.

There's more to it than just that, with fueling tables, VVT, etc. though as well.

Here's a visual guide

Thanks for the info. I realize there is much more than just torque, I'm like one of those kids, but why
It seems as if anything done to the Sonic with produce zero results without the tune. One of these days I hope to spring for your tune. Thanks again for the response.

 

[Stew]

...It seems as if anything done to the Sonic will produce zero results without the tune.

This is correct. You will not make more power without a tune. Actually you might make more power for a few minutes until the ECU realizes that something is up and corrects things back down to what it wants.

That's one way of doing it. You can also ask for more power than the engine will ever be able to make, and then hard cap boost so it always makes that much peak.

In a nutshell that is how I have mine, set the TQ tables higher than the engine is capable of achieving then set the max boost to what you desire, in my case 23 psi. I did get some help tuning at one point from Jerry (BNRacing), if you want a tune he's the man!

 

[ScarabEpic22]

Good explanation Stew and I know where the diagram is from Jerry! Helps a lot to put a visual chart together.

And KartRacer, you're absolutely correct. You'll see minimal gains without a tune, you could put a CAI, intercooler upgrade, full downpipe/midpipe/catback on and pick up a few hp/tq. Do the same mods with a tune, and completely different vehicle.

 

[nickalltogether]

Thanks for the info. I realize there is much more than just torque, I'm like one of those kids, but why
It seems as if anything done to the Sonic with produce zero results without the tune. One of these days I hope to spring for your tune. Thanks again for the response.

I think GM sets it up like this for a multitude of reasons, but the main reason I can see would be consistent performance for vastly different operating conditions.

 

[ScarabEpic22]

I think GM sets it up like this for a multitude of reasons, but the main reason I can see would be consistent performance for vastly different operating conditions.

Bingo. Same performance at all altitudes, octane, etc. Manufactures are using turbo/superchargers more as a fuel saving method vs performance so they build complex intake and exhausts to muffle all sounds.