Originally posted by 1stGenCRXer
It really depends on what grade of gas you use. Lower octane rating'd fuel burns faster than gasoline of a higher octane rating. If you gain fuel economy from retarding the timing, then you're probably using a lower grade of fuel than was originally intended for the engine, and once you've retarded the timing, the engine is able to better use the fuel burn to move the car. With a higher octane rating, you can get a longer useful fuel burn, so you'll need a bit of advance compared to a lower grade fuel.
At the same time, you can advance the timing to get a better throttle response, but throttle response doesn't equate to more power or better economy, just better throttle response. However, if your timing is advanced too far to make the best use of the fuel while burning, it'll get the piston moving faster, but not really have any follow-through. That make any sense?
you're right - the only way you benefit from a certain grade of fuel is to have igntion timing set accordingly.
When you advance to far, peak cylinder pressure occures when the piston is still on the compression stroke = detonation! on the other side, when you retard timing you get better top end power b/c of this reason: the faster an engine revs, the more timing it needs to completely burn the fuel in the cylinder (this can be up to 25 degrees more than base timing!), so when you retard timing you get more push on the downward power stroke of the piston like you stated in your quote, but less follow through, i.e. lots of push at one point (retarded timing) as opposed to a steady push through the whole power stroke (advanced timing). It also has to do with the rod to crank angle and bore/stroke ratio of the engine you have. I hope I was able to explain it well enough.
