just a general question about tunes

[Rockcrusher]

So, with any new car nowadays, tunes are a big deal. I frequently read positive things about them and how they transform a car's character (particularly the 1.4). I've read about increased power, sometimes better mileage and improved driveabiltiy as well. Given said tune is not so radical as to run the engine too close to its mechanical limits, my question is: why doesn't GM (in our case) have these cars leave the factory tuned like this? Not that the folks writing these aftermarket tunes aren't great at what they do, but with all its engineering might, why doesn't GM do this from the get-go? Why leave potential power and mileage on the table?

 

[JTee2017]

Questions I've had as well. I've read and heard various reasons from meeting EPA mandates to just running the engine for best over al performance in all possible weather conditions, altitudes, etc.

That said. . . . . this place struck my interest and I've read a number of reviews regarding the stage 1 OBD device. I do not know of anyone who has tried one in a Sonic with the 1.8L engine. It would be interesting.

https://www.performancechiptuning.com/chevrolet/sonic/
I have looked at two throttle body "response" type add ons and they also appear that they may improve throttle response, but at the expense of dinging MPG.

 

[Mike DZ]

GM engineering tunes for a combo of emissions, fuel mileage, longevity, under every possible conditions in the most cost effective method to keep engineering costs down to provides the customer enough performance so that they recover their investment and make bucks for the stock holders.

 

[skurtov]

MPG's. You add power, that means you need more air and fuel. Your fuel economy suffers in turn. GM has CAFE standards to abide to, not to mention the fact that you have to remain competitive in your class.

GM did however offer a ECU remap as an aftermarket addition paired with a Borla exhaust. But it's no longer offered.

 

[Rockcrusher]

Ok, here we go, next question. It has been repeated numerous times on this forum that if a modification is done without a tune, that, in time, the computer figures this out and returns power levels back to stock. How does it accomplish this?

For example, K&N states their intake systems give roughly 7-5 hp depending on the engine. Folks here claim the computer will eventually figure this out and revert power levels back to stock without a tune. How? If the intake allow more air into the engine, does the computer not compensate by adding more fuel to match the air? This is where the power increase is achieved. How can the computer take this power away? The intake is a "hard part" fixed to the engine. The computer can only control fuel at this point. If it removes the added fuel to kill power, the engine would run lean and pop a code. K&Ns don't set codes. So how is the power withdrawn?

Now, if an intake flows too freely, I understand there are limits to the computer's ability to adapt and this would set a code. Computers have to be somewhat adaptive as different stock replacement filters flow differently and further will flow differently as they get dirty.

As long as things are kept withing the computer's ability to adapt (something K&N surely researched in development), I don't understand how power can be restricted. Also, how does the computer know how much power the engine produces and how to keep output within a stock range? Its not like there is a dyno built into the car. I'm not trying to start an argument. I truly want to know how the car works but I don't want to merely accept a phrase I've seen parroted without some background info.

 

[Mike DZ]

Not a direct answer, but some food for thought -

Theoretically, an improved intake system provides better volumetric efficiency - https://en.wikipedia.org/wiki/Volumetric_efficiency - i.e. makes the engine breathe better. This increase in VE gets more fuel/air mixture into the cylinder for the same work, i.e. crankshaft rotation

Improved intakes work, I have used them on other vehicles (big V-8s), but I have no experience with K&N or intake changes on Sonics.

I do have some experience on gains provided by tunes on Chevy 4s and 6s and consider them the best bang for the buck.

 

[ScarabEpic22]

The E78 ECM the 1.4T uses is TQ based ECM, which means it calculates how much torque to let the engine deliver in a given scenario. I.E. you push the pedal down 30% at 2000 rpms, 90kPa (so not boost yet) and it says deliver 75ft/lbs of torque. The ECM then manipulates multiple systems, including boost pressure, cam timing, ignition timing, A/F ratio, and so forth to deliver that expected TQ to the wheels.

Why does this matter vs the older style GM systems that rely more on just making as much power as the engine can at that particular pedal/rpm/load breakpoint? Easier to manipulate for fuel economy, and the ECM sees the intake swap increases the airflow input and that it's easier to make the same amount of TQ at that breakpoint, so it just stops asking for throttle opening, more boost, so on. It's a target (PID) system where the ECM will only let the engine make what the ECM is programmed for, within a few hp/tq.

What does a tune do? Raises the desired TQ limit so the ECM doesnt limit power delivery. It also smooths out spark timing, cam timing, boost delivery, fueling, and shifting for autos.

Rockcrusher, the older GM ECMs will just throw a lean code as the ECM is expecting '10g' airflow at 3000rpms 90kPa and it sees 15g instead. The Sonic ECM will do this as well, but usually the ECM TQ limit is met before the fueling gets too out of whack, especially as there are few built/cammed/big turbo engines that would significantly alter this without a tune.

 

[Rockcrusher]

Ok, that explains it. Thanks!

 

[ScarabEpic22]

Here's a good basic outline of how the GM TQ based ECM "thinks", the same applies to the E39/39A/92 (basically everything from 2013+).
HPTuners - Working with the E78 ECM