Sorry for the dumb question

[crazie.eddie]

I hear talk about running rich or lean. What does both Rich mean? What does Lean mean? Sorry, I'm really a beginner when it comes to car stuff

[hoopdiewagon]

Rich means that you are runnin too much fuel. Lean means you arent running enough. Its typically thought its better to be rich than lean (why most manufactuers will purposely develop the ratios that way) but thats up for argument. Thats what the air fuel ratio is that you have seen (a/f). The ratio you are aiming for is about 14.2:1 on NA cars but FI are a little different. These ratios can be found on either a wideband tune which uses a different type of 02 sensor or on a dyno graph. The a/f is a very essential thing to know when the tuning starts! [8)]

[Mike-in-Orange]

Running lean can lead to burned pistons or worse, a major motor blowup. If you're running a boost controller and you haven't dialed it in correctly (tuned it) you run the risk of overboosting, which will cause you to lean out. Basically, you'd be feeding way too much air into the combustion chambers for the amount of fuel being fed, and that's when things can go horribly wrong. Don't ever just throw a boost controller onto your car and let 'er rip.....you'll rip the engine apart.

[quicksilverdon]

Agree with the above. Lean is the aim for fuel economy, but drives temps up, as mentioned. Once rode a motorcycle with twin carburetors - one of the carbs got loose and was sucking air - burned a hole in the piston the size of a dime!
Too rich wastes gas, dilutes oil, and doesn't run great.