igottafc

iTrader: (6)

Ok im just going to ask plane and simple. What does advancing or retarding the timing do on a turbo charged vehicle? what does advancing/retarding too much do to the way the motor performs? thanks -alex

edmcguirk

It takes time for the ignition to make pressure on the "piston". The ideal point for maximum cylinder pressure on a piston engine is about 15 degrees after TDC. I have no idea what is the best geometric configuration for maximum pressure in a rotary engine, but the goal is to time the ignition so that peak pressure happens at the right time.

Too early or too late and you lose power. Unless you have to compromise for detonation. Most (but not all) piston engines are limited by detonation so you can go up to higher octane and advance the timing to get more power. On some engines you can actually set timing too early and not have detonation.

The more pressure in the combustion chamber, the faster is the burn rate. The pressure is going up while the volume is getting bigger. If the ignition is too early the pressure will go up even higher while the chamber is not expanding fast enough. At some point the pressure will get so high that the unburned gasses will ignite before the flame front reaches it. That's a bad thing so you retard the ignition.

As you increase the boost, maybe the pressure goes up so high that you cannot get peak pressure at 15 degrees after TDC without detonation. You have to compromise and retard your ignition beyond the ideal amount just to keep your engine alive.

The real problem is that right now there is no easy way to measure peak combustion chamber pressure so you guess and listen for detonation and measure the HP on a dyno.

ed

igottafc

iTrader: (6)

1 more question, how does timing have an effect on exhaust temps?

edmcguirk

Late timing will start the combustion process late. The exhaust gasses will be hotter because the combustion process is still happening after the exhaust port opens.

ed

igottafc

iTrader: (6)

which can contribute to turbo glow. correct?

EpitrochoidMan

NEVER sacrifice ignition timing for compression (or boost).

Just my $.02

igottafc

iTrader: (6)

well i understand that. The only problem is that after hard use my turbo tends to glow almost white hot. i really dont have access to a timing light. The PO retared the timeing and i can see where the stock location was by the mark left by the nut. Its retarded about 3.5mm rotated to the right. Thanks -alex