Ignition advance map help needed

It could be done by a two stage advance mechanism (or a single advance plus a retard mechanism in this case), but I would of though it's more likely to be the advance mechanism peaks out at 3500rpm, then any ignition delay has a noticeable effect When the points/whatever signals the coil to fire, the process takes a fraction of a second before the spark occurs at the plug. With the engine doing 3500rpm, the flywheel is rotating at 21000 degrees per second or 21 degrees every millisecond, which at those rpm, a 0.1 millisecond delay will have the effect of retarding the ignition 2.1degrees.

Looks good enough for a base starting curve. You will need to advance/retard the ignition more depending up on the MAP signal (ie, no vacuum = full load, full vacuum = no load on overun), but it's something you'll have to experiment with to try and find something ideal for your engine, unless you want to pay a tuner to do it on a dyno.

Nedavno moray napisa:

What is usually difference between idle and full load ignition advance in degrees? And is the difference larger at low rpm and greater at high rpm or opposite?

I couldn't honestly tell you. It's been a good few years since I covered that stuff at college, and I've never had to worry about it, as little magic boxes do all that stuff automatically now!

If I get a chance, I'll have a dig through some of the books I've got that might cover it.

Nedavno Duncan Wood napisa:

I know, but there probably is a rule that applyes to most of the engines. It is easy to make a wrong map (I am not an experienced mechanic with all of necessary tools), so I wanted to make basis ignition map as good as I can.

Not really for vacuum advance, it's always been a bodgy solution, that's why electronic mapped ignition became so popular. Stick 10 deg in & then see how it runs, you probably ned a bit more at 60% load at high revs & a bit less at full load.

Its totally engine dependent and not something you can really guestimate at. Over at msextra.com you will get a good idea of what map you can work with but you cant really just put in a few setpoints and hope its right. To map the ignition table is an iterative and careful procedure which should be done on a rolling road with AFR details, torque output, det cans and ideally EGT output too. I suspect you have none of the above?

I've been tuning the ignition and fuel tables on my toyota engine (turbocharged so a little more complex) for quite a while, nudge up the advance and your apparent AFRs change, change your fuelling and your allowable timing changes.

All that said, the use of LPG *generally* increases knock resistance and therefore makes ignition harder - figures of 8-10 degrees extra advance across the map have been generally accepted, though the idle region will cope fine as standard.

I'll repeat though, ignition map tuning is a complex art, and it is an art, requiring time, patience and (without the correct instrumentation) acceptance that you may damage the engine before getting it right.

Nedavno Coyoteboy napisa:

You are correct, I have none of the above. But I found some useful information's at msextra.com Just as a starting point.

Searching on the Internet, forums and newsgroups (aus.cars is good) I found that LPG need more advance earlier in the revs, and less total.

I hope I do not do that.

If you avoid it pinking it's unlikely to be too bad, tuning a turbo for maximum power is a rather riskier art than lpg for maximum economy.