question about timing

[Toad]

Would someone explain to me what goes on with timing?

I am guessing that by advancing timing you are causing the spark to fire sooner and the opposite for retarding timing.

What makes it neccessary to retard timimg for forced induction or NOS and why?

Also what is the role that knocksensors play and how do they affect timing?

Does more oxygen as a result of FI or NOS cause the mixture to detonate sooner risking detonation prior to the piston reaching the top of the cylinder?

Also, I am somewhat confused by the whole degree thing. Is that the distance the adjustment is made on a 360 degree range with the starting point being zero? uh... +degrees advances timing -degress retards it..

This guess is way out there... changing the timing changes the position of the cams to open/close the valves sooner or later and the spark is controlled by the ecm based on the cam positioning sensor????

sorry about all the questions
Thanks :hail:

[red95gts]

Well... Let's differentiate between cam timing and ignition timing. For most cars, cam/valve timing is fixed to the crank angle for all practical purposes. In our cars, the camshaft/crank relationship is dictated by the timing chain. In some other cars (VTEC Y0!), the valve timing can be adjusted on-the-fly, but not in our beloved Rustangs.

When people refer to adjusting timing on our cars, they're talking about ignition timing. That's the point where the spark plug is ignited relative to the crank angle. As you advance the ignition timing, the spark happens sooner in the compression stroke (i.e the piston is further from Top-Dead-Center (TDC)). As you retard the timing, the spark occurs later in the compression stroke.

A knock sensor is a sensor that listens for spark knock (detonation) within the engine. When the sensor "hears" the detonation, it tells the computer to retard ignition timing a little until it goes away. It operates similar to an oxygen sensor in that it is constantly cycling. The computer will add timing until the faintest bit of detonation is detected, then back it off until it's gone, then repeat the cycle over and over. This way you have maximum ignition timing over a range of operating conditions. The thing that makes these difficult to implement is the sensors themselves are tunes to a specific frequency. Each family of engines will make a different frequency spark knock and once the engine is modified, that can even change some. So, you can't go grab a spark knock sensor off an import 4-cyl car and bolt it up to one of ours. It may trigger on some noise within the engine, but it will most likely not be detonation...

[Toad]

great response, thanks man.

with forced induction (8psi @ 10:0:1 compression) on a stock bottom, the factory timing is safe?

[Saleen91]

It is if you're going to run race gas, but not with pump gas.

[MUSTANG BILLY]

Welcome!