What is a custom tune?

wrabbi2 said:

I know this shows how stupid I am but I need the info. I want to put a new air intake on my 08 GT 500. Everything I read states that if I do this I also need a custom tune. I can even buy the intake and tune together in a kit. The problem is I am vague on what a custom tune is. I see the little devise in the adds, and obviously it tunes the engine, but could someone expalin in laymans terms what is actually does and what are the steps involved in the process of doing it? Do they come with directions and is this something a novice should attempt?

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Your car's engine computer measures a variety of variables (inlet air flow and temperature, throttle position, engine rpm, etc.) and makes adjustments to fuel flow and valve timing etc to provide smooth, safe, efficent power based on a program or "tune" that is to some extent specific to the combination of parts that it was designed for. When you changeout some parts (cold air kit, exhaust system, supercharger pulley) the tune needs to be updated so that the computer can make the appropriate adjustments for the new hardware.

There are at lease two levels of "custom tunes". The first level is a canned tune that you get that is not specific to your individual car but has been prepared to be close to optimum for cars like yours (ie with the same modifications). The second level is a true custom tune which is prepared by a tuner specialist with your car on a dynamometer. Typically a canned tune will be loaded onto your car's computer and then over successively higher RPM passes, the tune is adjusted and reloaded onto the computer until it is confirmed appropriate for the specific combination of components and operating parameters of your vehicle.

Typically a tune is loaded (or flashed) into the computer using a handheld flash device (XCAL, Diablo, etc). Normally you will make a copy of your base tune from the computer to the flash device and then load the new tune from the flash device into the computer. The port for connecting the flash device to the computer is under the dash by the steering wheel. The instructions are pretty simple for loading a canned tune and can easily be handled by a novice. For a true custom tune you need to book time with a professional tuner with a dyno.

I had my car on the dyno earlier this week - a video of one of the dyno runs can be seen/heard at the link below:

'07 GT Dyno Pull