warming up?

cre · 10-20-2009, 07:15 AM

There are two types of timing, doesn't matter if the car is N/A or Turbo: mechanical and spark.

Mechanical timing is where you align everything so that piston #1 is at 0? or TDC (Top Dead Center) and the valves are precisely where specified by the manufacturer and the distributor and cam position sensor (yes our N/A's do have a CPS inside the distributor) point to the #1 position.

Spark timing define when the spark occurs with relation to the location of the piston. The spark is actually generated in *advance* of the piston reaching TDC; hence the term "spark or ignition advance". The thing is that what you're trying to achieve here is a situation where half of the fuel in the cylinder has been burned by the time the crank reaches about 20? ATDC (After Top Dead Center) as this is where the most power is made. So, in order to acheive this the ECU adjusts the spark advance constantly while listening to the knock sensors to hear is the spark occured too soon causing a shock to the system (this occurs if the advance is too great and the fuel is igniting sooner than predicted). As a result of these factors if your timing is too far advanced or retarded you may see a power loss (and possibly a severe one) and your engine and exhaust temps will change. Your spark timing and the burn rate of the fuel is important in determining the octane you want to use in your vehicle. Too high and may lose power... too low and you may lose power... interesting eh?

Setting the ignition timing on these cars is very easy... so easy that it seems a lot of mechanics just can't manage the feat.

EDIT:Oh, and I didn't say I wouldn't help... just not about to take anyone by the hand and walk them through the wonderful world of automotive repair and modification. I am willing to help you out here and there.

cre · 10-20-2009, 07:29 AM

I should add that the ECU has a couple different maps or charts that it uses to determine the base ignition timing for a given engine temp, air temp, RPM and throttle position. The map used when the engine is cold is fairly conservative. The only map which is more conservative is the "limp mode" map which pulls a LOT of the advance out, this results in a very weak engine performance wise and can result in a rather hot engine due to the pulled timing. Limp mode is engaged when certain error codes are registered by the ECU (such as code 52: knock sensor error or malfunction).

Your spark advance and mechanical timing also affect the temperatures within the engine. Burn the fuel too soon and you've got a LOT of heat which has to go somewhere and the valves aren't letting it out... Burn the fuel too late and it's still burning when the valves open... cooler engine, HOT exhaust and as such hot O2 sensor and hot hot hot valves.

10-20-2009, 07:15 AM	#1
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	There are two types of timing, doesn't matter if the car is N/A or Turbo: mechanical and spark. Mechanical timing is where you align everything so that piston #1 is at 0? or TDC (Top Dead Center) and the valves are precisely where specified by the manufacturer and the distributor and cam position sensor (yes our N/A's do have a CPS inside the distributor) point to the #1 position. Spark timing define when the spark occurs with relation to the location of the piston. The spark is actually generated in advance of the piston reaching TDC; hence the term "spark or ignition advance". The thing is that what you're trying to achieve here is a situation where half of the fuel in the cylinder has been burned by the time the crank reaches about 20? ATDC (After Top Dead Center) as this is where the most power is made. So, in order to acheive this the ECU adjusts the spark advance constantly while listening to the knock sensors to hear is the spark occured too soon causing a shock to the system (this occurs if the advance is too great and the fuel is igniting sooner than predicted). As a result of these factors if your timing is too far advanced or retarded you may see a power loss (and possibly a severe one) and your engine and exhaust temps will change. Your spark timing and the burn rate of the fuel is important in determining the octane you want to use in your vehicle. Too high and may lose power... too low and you may lose power... interesting eh? Setting the ignition timing on these cars is very easy... so easy that it seems a lot of mechanics just can't manage the feat. EDIT:Oh, and I didn't say I wouldn't help... just not about to take anyone by the hand and walk them through the wonderful world of automotive repair and modification. I am willing to help you out here and there. Last edited by cre; 10-20-2009 at 07:17 AM.

10-20-2009, 07:29 AM	#2
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	I should add that the ECU has a couple different maps or charts that it uses to determine the base ignition timing for a given engine temp, air temp, RPM and throttle position. The map used when the engine is cold is fairly conservative. The only map which is more conservative is the "limp mode" map which pulls a LOT of the advance out, this results in a very weak engine performance wise and can result in a rather hot engine due to the pulled timing. Limp mode is engaged when certain error codes are registered by the ECU (such as code 52: knock sensor error or malfunction). Your spark advance and mechanical timing also affect the temperatures within the engine. Burn the fuel too soon and you've got a LOT of heat which has to go somewhere and the valves aren't letting it out... Burn the fuel too late and it's still burning when the valves open... cooler engine, HOT exhaust and as such hot O2 sensor and hot hot hot valves.