legacycentral bbs

Been doing alot of reading, trying to get a graps on a few terms that some of you throw around like I can Unix terms.

EGT - Exhaust tempature guage. makes sense... what does knowing your exhaust tempature tell you about how your car is working ?

AFR - Air fuel ratio.. once again how can you use this tool to know how your engine is working well ? While I'm at it, how does it relate to Stoichiometric pressure ? and why is stoich pressur at boost not a good thing ?

Boost/Vacuum guage - I know the use of a boost guage no problems. What use it is to know how much vacuum your car is under. at any one time ?

What does "IDC" mean ?

How/What does a narrow/wide band o2 sensor do ?

I guess most of these questions are pretty basic, but i thought a whole thread dedicated to it might be helpfull for other learners like me.

thanks folks.

EGT - You know how hot the engine is running by the heat of the exhaust. It's helpful for knowing richness, as well as the overall condition of the engine. Abnormally high or low EGT's would denote a out of whack tune. You can also tell timing and things like that. It becomes very useful when you know what would effect EGT's and what each of those things would do to the EGT's. Unfortunately, most EGT probes don't react very quickly enough to tell you when something is wrong before it's already wrong. Unshielded probes are better, but wear out quickly.

A/F gauges - Tell you how rich or lean or stoich the engine is running. Rich is to much fuel, lean is to little, stoich is even a/f ratio. Rich is safer than lean, but it hurts performance. Lean is caused by not enough fuel getting to the engine, your EGT's jump when you are running lean, and usually drop when you are running rich. Stoich is even, I don't remember the value off the top of my head. Under boost, you want MORE fuel just as a saftey measure. Boost conditions are so volitile (in terms of the environment, things are always changing) that if you run stoich one day, you'll run full-lean the next and blow the engine. A fly farts and the tune of a turbo engine can change.

Boost gauges are good for leak testing and tuning. You want to know if you leak at boost, or if you have a vacuum leak. You absolutely HAVE to know what the boost is doing if you modify anything. Vacuum is just a thing that is good to know. Plus, I like seeing the gauge sweep across 50% of the gauge

IDC is Injector Duty Cycle. 100% is the maximum amount that the injectors can possibly flow. Ideally, you want to make most of your power below 80% just to give yourself some cush-room incase something gets FUBAR. ALWAYS overbuild and underproduce.

Narrow and wide-band O2 sensors just give a better resolotion to the fuel maps. Narrow bands are, essentially, on/off style. Wide bands see wider ranges of readings and produce a better "picture" of the oxygen maps. Better resoloution gives the computer a better idea of how much fuel is needed.

this is exactly what i was loooking for thanks !