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3.
A person that overcomes the factory limitations of their vehcile to gain more power, lower times at races, and/or better handling.

When emmissions standards were introduced, many tuners gave up, but others learned about HC, CO, NOx, CO2 and were able to improve those numbers.

When electronic controls were introduced, many other tuners gave up. but others learned the way they worked, and were able to make performance gains in their cars.

What stands in the way of tuners now, is quite frequently, illogical laws that ban tuning outright, despite the fact that a well tuned engine can have lower HC, CO, NOx, CO2 and fuel consumption than one in factory specification. The same goes for swaps, even though the emmissions of a S15 SR20DET are less than a 1989 KA24E, many areas have laws that declare the Silvia Conversion illegal anyway. If you think that Japanese cars are the only ones affected, think again. Many Chevy guys have fitted LS1/LS6 and LT1/LT4 engines to older cars, bringing lower emmissions and fuel consumption in the process. European imports are also affected, as a popular swap is to take a 1.8 turbocharged engine from a VW MKIV chassis, and fit it to a MKII Golf or GTI. Still, many areas have laws written by people who don't know any automotive physics.
Any car with altered factory parts, fabricated parts, or specialty aftermarket parts is considered a tuner car.

Any driver who builds or installs those parts is a tuner. Tuners also adjust things like the mixture screws on a carb, or the programming of EFI.
by Artificialist October 27, 2005
 
1.
A person who tunes ANY type of vehicle.
(Can be anything from a Honda s200 to a 1970 Dodge Charger) This breed of human lives, eats, and dreams cars. This person does performance mods BEFORE apperance mods, unlike the ricer.
Ricer: Your're such a ricer!
Tuner: You wanna drag race to see who is the real ricer?
Ricer: Okay

Not only does the tuner leave the ricer in the dust, but at the finish line, he's doing doughnuts ad burnouts.
by Agent Smith September 10, 2004
 
2.
COMPLETE opposite of ricer. The tuner is all go no show. What is UNDER the body of the car is far more important than how the car looks. For example the tuner will actually have no stickers on his car from where he got his parts, while the ricer will have stickers all over his car from parts he doesn't have.
There has been a battle on the streets for years between tuners and ricers.
by louie7 September 01, 2006
 
4.
A car, usually imported, that has been modified to increase both appearance and performance.

Not the same as a ricer.
The tuner drove by us with insane speed.
by Fakeman Fakey May 08, 2004
 
5.
{noun}

Any car, like a domestic car (Dodge Neon) or an import (Nissan Skyline), that has aftermarket parts (Brembo, Eibach, you get the picture) installed on it. Most commonly mistaken for a ricer.

(Mind you, muscle fans insult tuner owners mainly because they think tuners are ricers. However, this claim is not true. Remember, there are sleepers.)
I've hated muscle fans ever since one of them called my Eclipse (which is a tuner) a ricer.
by I dunno lol. November 03, 2011
 
6.
Any device, usually a can or bottle, used to spit the saliva or juices into, while chewing tobacco. Tobacco juices are not usually pleasant to swallow and irratate the throat, and can induce the feeling of vomiting.
I want to dip some copenhagen in class, but i need a tuner.
by JimmyKid July 10, 2008
 
7.
1. A electric device used for tuning a musical instrument to its proper pitch
2. One who professionally tunes a musical instrument
1. My tuner indicates that this guitar string is too sharp (high)
2. The piano sounds really bad. We should call in a piano tuner some day.
by Bill M. July 27, 2004