Hondata

I am potentially going to be trying some ignition advance, hunting for peak power (probably with some water injection, so it's important I spot peak power as the mixture will resist detonation quite well).

I realize it is possible to over advance the ignition to the point where you lose power, and you want to, in a boosted car, to tune to just under max power... ie, the least advance you need to run to make just under peak power.

What I'm wondering is how much forgiveness I will have when advancing ignition -- can I do a few pulls with it, say, 2 degrees overadvanced, like where I've just started to lose power, without damaging the motor? What kind of window of 'over advance' do I have to spot power loss before the extreme stress on the rods and bearings starts to become a danger. How much does the risk of damage increase with each 2 degrees past ideal ignition? Right now I'm at 7psi on the jackson charger, but I may soon be at 9 or 11 with water injection.

Wayne

Typically you do an entire dyno run unless you hear audible knock, then you add some timing and do another run...you do this until you loose power then back of a few degrees.

I can't really answer the forgiveness question, because that involves too many variables. You may want to talk with a tuner and get their view point on this, as they have much more experience on the dyno than I do.

I think that as long as you are not detonating, there is no danger in overadvancing the ignition. If you advance too much, (and no detonation ocurrs) the power just falls off and you are actually putting less stress on the engine than with full power "optimal" timing run.

If you get detonation under any conditions (advanced or not) that is bad, probably time to abort the run and fix what ever parameters led to the deto.

Corey872 wrote:I think that as long as you are not detonating, there is no danger in overadvancing the ignition. If you advance too much, (and no detonation ocurrs) the power just falls off and you are actually putting less stress on the engine than with full power "optimal" timing run.

If you get detonation under any conditions (advanced or not) that is bad, probably time to abort the run and fix what ever parameters led to the deto.

I was under the impression that it's more stress because you're compressing an expanding mixture -- like pre-ignition does. Doug stated it was very stressful to be overadvanced and not detonating in the kpro dvd.

Razathorn wrote:I was under the impression that it's more stress because you're compressing an expanding mixture -- like pre-ignition does. Doug stated it was very stressful to be overadvanced and not detonating in the kpro dvd.

You are correct.

Razathorn wrote:

Corey872 wrote:I think that as long as you are not detonating, there is no danger in overadvancing the ignition. If you advance too much, (and no detonation ocurrs) the power just falls off and you are actually putting less stress on the engine than with full power "optimal" timing run.

If you get detonation under any conditions (advanced or not) that is bad, probably time to abort the run and fix what ever parameters led to the deto.

I was under the impression that it's more stress because you're compressing an expanding mixture -- like pre-ignition does. Doug stated it was very stressful to be overadvanced and not detonating in the kpro dvd.

I guess I don't quite follow the "more stress because you are compressing an expanding mixture" part.

By that logic, any ignition advance beyond 0 TDC is actually compressing an expanding mixture. If you have a spark at 30 BTDC, aren't you compressing an expanding mixture for roughly 30 degrees of crankshaft rotation?

From the (admittedly few) dyno runs I have seen, it seems pretty common to make a run, bump the timing a couple degrees and make another. If power is up and no deto, bump a few more and run again. If either deto or power loss show up, that is the end, bump back the few degrees to the higher power run and call it done. Within +/- a couple of degrees, I don't think there would be a huge difference. Now if you go skipping through the curve 6 or 7 degrees at a step, that might get ugly pretty quick!

I would certainly respect Dougs opinion over my own ramblings any day, though.

Corey872 wrote:

Razathorn wrote:

Corey872 wrote:I think that as long as you are not detonating, there is no danger in overadvancing the ignition. If you advance too much, (and no detonation ocurrs) the power just falls off and you are actually putting less stress on the engine than with full power "optimal" timing run.

If you get detonation under any conditions (advanced or not) that is bad, probably time to abort the run and fix what ever parameters led to the deto.

I was under the impression that it's more stress because you're compressing an expanding mixture -- like pre-ignition does. Doug stated it was very stressful to be overadvanced and not detonating in the kpro dvd.

I guess I don't quite follow the "more stress because you are compressing an expanding mixture" part.

By that logic, any ignition advance beyond 0 TDC is actually compressing an expanding mixture. If you have a spark at 30 BTDC, aren't you compressing an expanding mixture for roughly 30 degrees of crankshaft rotation?

From the (admittedly few) dyno runs I have seen, it seems pretty common to make a run, bump the timing a couple degrees and make another. If power is up and no deto, bump a few more and run again. If either deto or power loss show up, that is the end, bump back the few degrees to the higher power run and call it done. Within +/- a couple of degrees, I don't think there would be a huge difference. Now if you go skipping through the curve 6 or 7 degrees at a step, that might get ugly pretty quick!

I would certainly respect Dougs opinion over my own ramblings any day, though.

You advance ignition before TDC so the piston will be traveling down as the mixture ignites at the best possible time. Ignition does not happen instantly and if you ignite right at TDC, your piston will be well through part of the power stroke before the mixture starts pushing down. By advancing the ignition, you are timing when the piston reaches TDC with when the mixture starts to burn and expand -- which means starting it slightly before it gets there based on engine load and engine speed. When you advance it too far, the piston will get there too late and the mixture will have already started expanding. Generally speaking, detonation is likely when this happens, but not a requirement or always the case -- that's why tuning to knock alone is a bad idea.

With my crap 91 octane fuel around here, I doubt I could be overadvanced and not realize it via knock count, but when I throw water injection in there, something that makes the mixture far less likely to detonate under pressure, the possibility presents itself quite quickly.

Wayne