EFI University

[Repoman]

[El Verdugo]

24psi on 92 octane, interesting. Really pushing that octane level?
Good power level.
_________________
Alberto I Correa, Jr.
EFI 101 Graduate 7-16-05
AEM EMS factory trained
www.corrperformance.com

[Repoman]

Thanks I beleive i am giving up more power under the curve.
I'd like some one in the KNOW to look at the ignition curve and offer some advice on if it looks funny?
3krpm -32 4krpm -32 5krpm -32 6krpm -32 7kpm -31 8krpm -32
I think i should go
3krpm -32/ 4krm -34/ 5krpm -36/ 6krpm -34/ 7krpm -32/ 8krpm3-1 9krpm -32

[Turboivo]

Repoman, my unpretending impression is that people in the KNOW on this forum usually don't like to guess the ignition advance, especially on unknown setups. You should use the dyno and see what your engine wants.

[Repoman]

I understand that. Every engine is different.
I would just like to confirm that a "tipical" ignition curve should be
all in by 3000rpm retard to TQ/HP crossover then advancing to red line?
I look at my timing and dyno plot compared to other turbo plots and see mine is flat and climbs linier to red line. others peak early and drop to red line.
I can only assume this is due to there mechanical makeup I.E. Cam/ head flow/ Turbo/ Exhaust and timing stratigy.
I just would like to adress timing stratigy.
Which is Better/Correct?

[baldur]

What spark timing basically represents is the inverse of combustion speed. If not knock limited, you'll want just enough advance to complete combustion just as the piston leaves top dead center. However, combustion speed is affected by a number of things, one major factor is turbulance in the combustion chamber during combustion. This is engine speed dependant and explains in part why there's no single strategy that fits all engines.
In general, on 4 stroke engines, you'll want low advance at low speed because there's ample time to complete the combustion, then advance quite rapidly because the fact is, combustion is slow at low speeds because the charge is stagnant when the piston has stayed near TDC for a long period (a function of engine speed, engine stroke and rod to stroke ratio).
If you ignite a regular hydrocarbon fuel and air mixture that is under pressure but in static conditions, it's not exactly explosive, the flame front just burns up the mixture in all directions from the spark plug at a rather steady rate. In a high speed engine however, the mixture is not static, it has gained kynetic energy during induction and compression and it's still moving when the spark ignites it, this greatly accelerates the combustion as the flame front moves with the charge. At high engine speeds the charge is likely to have more kynetic energy at the time of ignition, more turbulance to spread the flame front, to explain why the engine doesn't necessarily need more timing at higher speeds, it may even need less timing if it breathes well at high speeds, up until where it's past peak power.

When you get to the matter of chamber size and shape, a squish chamber leaving less distance for the flame front to travel before it has reached all of the combustible charge and more turbulance as most of the charge is ejected out of the squish band nearing TDC, thus in theory, less time required to complete combustion.

Unfortunately the only way to really figure out what a particular engine spec needs calibration wise is to experiment.