what is timing on tunning?

[mehrshadvr4]

i heard alot about good timing on tunning .dose it mean timing belt or ignition timing or fuel timing?

[2old]

In our cars or in general?

In our cars the only thing you can change is the cam timing if you bought adjustible cam gears. The objective here is to tune the where the optimum valve overlap occurs to change the torque and HP curves (Currrently our cars timing should be optimized for around 5-6000 RPM... I would need to check the graphs to be sure).

If you are using the car for racing you can change the time the valves overlap to try to maximise HP at high rpms (this reduces your overall torque at low RPM which actually makes your car slower when accerating from a dead stop) but you need a dynometer to do this because unless you have supercomputer to model the flow there is no hard and fast rules about adjusting the cam timing.

In general (IE only apply to SOHC versions of our cars that have distributer or aftermarket modded ignitions) you can adjust the ignition timing to advance it so that the flame front will hit the piston when it reaches just after TDC (Top dead center) which would maximize power. In general you want the flame front to reach AFTER TDC because if it hit before it puts a lot of stress on the crankshaft and robs you of power in a hurry.

Technically Fuel timing is not as critical in gasoline engines as it is sprayed into the pre-chamber and doesn't do anything (except maybe leave deposits) if it is done early. In diesels or cars with direct fuel injection this is more critical as it is used to cool the ignition chamber to prevent pre-detonation so that the engine can be designed with a higher compression ratio.

[talskinyguy]

We also do ignition timing, which is generally what people are talking about when they talk about how many degrees of timing advance they have.

[talskinyguy]

Originally Posted by 2old

In diesels or cars with direct fuel injection this is more critical as it is used to cool the ignition chamber to prevent pre-detonation so that the engine can be designed with a higher compression ratio.

Diesels do not work like that. Diesel fuel timing is equivilant to gas ignition timing. It is not used to cool the ignition chamber, and you dont need to prevent pre-detonation, because without fuel it is imposible.

[2old]

Originally Posted by talskinyguy

Diesels do not work like that. Diesel fuel timing is equivilant to gas ignition timing. It is not used to cool the ignition chamber, and you dont need to prevent pre-detonation, because without fuel it is imposible.

Sorry, you are right... I was just over-simplifying the use of direct injection... Otherwise I would end up writing an entire article on the physics of combustion...

[Igovert500]

No, he is talking about ignition timing I'm guessing.

First read this:
http://www.stealth316.com/2-ignitionsystem.htm

especially the parts halfway down about ignition timing control and how it relates to knock.

Okay, got the basic idea from that?

When people go with larger turbos, larger injectors are necessary. You use fuel controllers to fool the ECU into controlling these larger injectors as if they were still stock, by lowering the air flow signals. This is fine for injectors up to 550s.

However, after 550cc injectors, the airflow signals are reduced so much, that timing becomes an issue. With larger or oversized injectors the ecu thinks the airflow and load are extremely low and doesn't see knock, so it thinks it's safe to advance the timing. As the ECU only sees the 'corrected' information, it can actually advance timing beyond a safe threshhold, without even realizing it. And lots of boost + really advanced timing = BOOM.

So many get something like the Greddy E-manage which allows them to bring down their base timing from 5 degrees to 0. And then specifically advanced or retard timing throughout the rpms as needed.