3 forms of timing?

[Dave]

Seems like I've been posting a lot in this section... meh.

Well after hooking up the scanner to my car I am watching the timing advance and whether or not it's pulling timing.

So as I looked at the timing advance it usually stays anywhere from 9-28. Depending how fast I'm going at certain RPM's.

My question is this: I thought there was only 2 forms of timing - base timing and cam timing. So what is this computer-controlled timing? How is it different from the other two? How is it controlled?

Thanks in advance.
-Bryan

PS: Sorry for all the questions lately, just trying to learn.

[GLHS60]

Cam timing is the camshaft in relation to the crankshaft via the timing belt. It can be advanced or retarted slightly but not with the engine running.

Ignition timing is the firing of the spark plug in relation to the piston. eg. 8 degrees before top dead center. The computer is constantly changing ignition timing to obtain optimum performance and economy while the engine is running under varying conditions.

What we are mainly concerned with is total ignition advance under wide open throttle full boost situations. Too much advance will result in detonation which basicly is the air fuel mixture exploding in the cylinder, hence detonation, rather than burning rapidly. The difference can be a matter of only a few degrees so it is a critical element. The marvel of our hall effect ignitions is it can retard spark advance in only one cylinder if necessary to obtain maximum performance under varying conditions.

Thanks
Randy

[5sp. mini]

chirs or paul might be beter at this but like the old mechianal adv. was with springs and wieghts. to get a timeing adv. at wot but not at low rpms, but i don,t know what or how the ecm contorls the dist. adv.AL

[turbovanman²]

The computer controls the timing at all rpms, it does this for maximum power, maximum fuel economy and best running engine. It uses the knock sensor, tps, map, coolant temp etc to calculate what the engine wants and of course, using its program to give us the best spark curve.

[Dave]

Thanks guys. :)

So if the computer controls the base timing, why do we even bother setting it to like 12 or 14 degrees if the computer changes it anyways??

[turbovanman²]

Thanks guys. :)

So if the computer controls the base timing, why do we even bother setting it to like 12 or 14 degrees if the computer changes it anyways??


The computer doesn't control the base timing, you set it. I guess the engineers prefer to advance timing than retard it.

[GLHSKEN]

Thanks guys. :)

So if the computer controls the base timing, why do we even bother setting it to like 12 or 14 degrees if the computer changes it anyways??

The computer only ads or subtracts timing to the base dependant on the inputs from the sensors. It does not know the total timing it can only "ASSume" you set it correctly.

[Dave]

The computer only ads or subtracts timing to the base dependant on the inputs from the sensors. It does not know the total timing it can only "ASSume" you set it correctly.

Maybe I'm totally retarded but if I set the base timing to 12* what's the point of doing so if the computer is just going to change it overall anyways??

[GLHSKEN]

The computer KNOWS base is supposed to be 12. It expects it to be there.... It's changes are made from the inputs of the sensors and it adjusts.

If you SET it to 14 your timming will be 2^ higher throughout the operating range. The computer does not say.. Hmmm timing should be xx degrees here... I don't care what bryan set it at. I want to make it XX... The computer DOES say... based on the inputs from the sensors i NEED to either ADD or SUBTRACT timing.

[glhs422]

If you SET it to 14 your timming will be 2^ higher throughout the operating range. The computer does not say.. Hmmm timing should be xx degrees here... I don't care what bryan set it at. I want to make it XX... The computer DOES say... based on the inputs from the sensors i NEED to either ADD or SUBTRACT timing.

Thanks for clearing that up, Ken - I thought I had a hold on the whole timing thing but I never realized that!
__________________
Eric Shelton
'86 GLHS #422 - 13.232@106.046 - Sac Raceway
’02 Camaro SS M6 – 12.78@115 (corrected time and mph; Los Angeles County Raceway)
My Website (http://ecf2.puc.edu/Students/edshelton/pickacar.html)

[GLHSKEN]

It's all based on tables...

[turbovanman²]

It's all based on tables...

And thats what tuners play with, they can help the turbo spool slower, faster etc by playing with timing.

[Dave]

The computer KNOWS base is supposed to be 12. It expects it to be there.... It's changes are made from the inputs of the sensors and it adjusts.

If you SET it to 14 your timming will be 2^ higher throughout the operating range. The computer does not say.. Hmmm timing should be xx degrees here... I don't care what bryan set it at. I want to make it XX... The computer DOES say... based on the inputs from the sensors i NEED to either ADD or SUBTRACT timing.

Lamen's terms everybody! :thumb: Thanks Ken. I get it now.

[GLHSKEN]

LOL :thumb: