indyspeed

I'm new to tuning... Can someone explain to me what the goal of tuning is (other than the obvious to get more HP)? In other words, are you trying to get the engine to run leaner typically? Can that cause reliability or longevity issues? If you can gain 20-30 HP or so from tuning, why isn't the factory or GM offering custom tunes for Corvettes? My apologies for these basic questions, but before I invest in something like HP Tuners of EFI Live I really want to understand why you would actually tune the car and what side effects that might have.

0ian@thetuningschool

The goal of tuning is to get the best power out of the car and driveablity. I am not to sure why gm cant tune your car for a extra price, probably to lazy and cost to much money and time. You typically gain 10% from tuning a stock car and can gain 3-5 mpg. The tune from gm is generic tune so that your car will perform the same if you go from Alaska to say Florida or Denver. With tuning you are optimizing your car for your environment.

Ian

TurboLX

...or they have to meet both Federal and California (14 states, actually) emissions standard to make the car legal for sale. They also have to put safety checks in place to prevent catalyst damage under sustained high load use and live for 100k+ miles. How many aftermarket "tooners" provide this kind of warranty without any limitations on where you can drive it (anywhere from Alaska to Denver to Miami to Death Valley) and when? Sure it costs a few max HP, but it sure beats walking home.

Tuning isn't only about getting more power than someone else. It's really about making the PCM's math model match the hardware on the car. If the PCM and engine are properly matched (calibrated to one another), then you get the best possible emissions, driveability, AND safe power. Whenever you change the engine hardware significantly, it's a good idea to take another look at the tune to make sure things are still lined up. A properly calibrated PCM shouldn't have large learned fuel trims, poor economy, or potential hardware damage.

indyspeed

Thanks for the info. I do find it interesting that it is mentioned that tuning is to provide balance or proper calibration when you change your hardware. It seems to me that if you install additional hardware other than simple mods such as a CAI or headers you can put significant additional stress on the vehicle components. In that case, I don't see how a tune could prevent hardware damage if the other stock components are not up to task. Nonetheless, maybe I should ask the question a different way. In short, if you have a stock car, why would you modify the stock tune (other than to void your warranty). I mean I hear you can gain maybe 20HP by doing this, but it sounds like based on replies that this might give you problems in regards to drivability, emissions compliance, and "safe power" because the stock tune already does that presumably. It also seems like a lot of effort to only gain perhaps 4 to 5% additional power. Obviously, that might be worth it to a hard core track person to squeeze every ounce of additional assistance, but for someone that will only occasionally go on the track I'm not sure they would notice...

Shortimer

One other point worth mentioning, if you "tune" and have a problem that requires a visit to the GM dealer because the car is under the factory warranty, your warranty "might" be voided. GM techs can detect tunes even after the original program has been returned and the tune removed. Good luck with any tuning you go with.

Mez

The most common reason to modify the PCM software (i.e. "tune") is because of a change in the airflow characteristics of the engine during various conditions. Not everything translates to more peak power. The common causes of this would be changes to the cam, ported heads, tube headers, and forced induction. The factory PCM has tables that provide fueling and ignition advance setting at different engine loads, speeds, coolant and air temperature based on the factory hardware. There is also the STFT & LTFT or "learning" functions as a result of the feedback from the O2 sensors. These are affective in a limited range of change in the air flow characteristics. These tables should be re-calibrated to reflect the new airflow characteristics.
Another reason is the factory tables are fairly conservative. The fuel power enrichment tables are rich at WOT to keep the cat temps lower and extend their life. By leaning these PE table out a little, will increase power.

The ignition advance tables are also conservative since the available fuel octane range from 91 to 93 depending on what part of the country. In my case, I was able to add 4-5 degrees of advance at WOT without any knock since we get 93 octane here in Austin.
Finally, there are other less critical function that improves drivability such as removing CAGS, having radiator fans to come on at a lower coolant temp, increasing idle speed to prevent stalling, and others.

1badzo6

Do you know exactly how they can tell.

The few tuners Ive talked to say GM cannot tell once the calibration is returned to stock.
While there is the talk out there saying they can.
Thanks.