88 replies to this topic

[Horses With Gas]

What settings do you have for proper adjustment (maximum vac readings at idle, minimized overlap & range of powerband emphasized)?

Edited by Horses With Gas, 21 October 2011 - 04:07 PM.

[98t5M]

Sorry if this has been brought up before but I haven't seen a mention of it;


Does changing the cam timing also effect ignition timing?
Since the rotor is bolted to the intake cam, if you retard the intake cam wouldn't you effectively be retarding the ignition timing too?
And since the cam position sensor is on the exhaust, doesn't the ecu really have no way of telling where the intake cam is, and consequently how it may be effecting ignition timing advance?
Or am I missing something here?

Any info you guys have on this would be appreciated.
Thanks

[ozzimark]

Ignition timing is controlled electronically. The distributor has enough overlap that advancing it or retarding it won't affect the spark at all.

[98t5M]

ozzimark, on 03 January 2012 - 03:32 PM, said:

Ignition timing is controlled electronically. The distributor has enough overlap that advancing it or retarding it won't affect the spark at all.

I realize the ECU controls ignition timing, but how does it know where the rotor is in relation to crank position, in order to compensate for the cam being advanced or retarded?

I'm not trying to argue or say you're wrong, I'm really just curious.

Edited by 98t5M, 03 January 2012 - 05:35 PM.

[the commissar!]

Putting together pieces of info leads me to believe the following but I'm not an expert...

it doesn't know exactly if you adjust the cams, but even if it did there is a range that the ignition timing can fire in and it is at least 40 degrees (part of your tuned maps via Turbotuner or IPD or Lucky or whoever). Each CAM is only adjustable by ~7 CRANK degrees and the car will not run worth crap at the extremes so you won't be off by too much, not for long anyway.

[ozzimark]

98t5M, on 03 January 2012 - 05:34 PM, said:

I realize the ECU controls ignition timing, but how does it know where the rotor is in relation to crank position, in order to compensate for the cam being advanced or retarded?

I'm not trying to argue or say you're wrong, I'm really just curious.

It doesn't compensate because the design makes it not matter

[98t5M]

the commissar!, on 03 January 2012 - 07:17 PM, said:

Putting together pieces of info leads me to believe the following but I'm not an expert...

it doesn't know exactly if you adjust the cams, but even if it did there is a range that the ignition timing can fire in and it is at least 40 degrees (part of your tuned maps via Turbotuner or IPD or Lucky or whoever). Each CAM is only adjustable by ~7 CRANK degrees and the car will not run worth crap at the extremes so you won't be off by too much, not for long anyway.

I thought the cams have 7.5deg of adjustment each direction for a total of 15deg, which works out to 30 degrees of crank rotation


Ozzimark, thanks I see what I was misunderstanding now, I was thinking of it like an old school distributor where the rotors relationship to the cap actually effected timing, but i now understand it doesn't make a difference on our kind-of-sort-of modern ignition systems. (So long as the relationship isn't so far off to make the wrong spark plug fire )

Edited by 98t5M, 03 January 2012 - 10:47 PM.

[lookforjoe]

98t5M, on 03 January 2012 - 10:32 PM, said:

(So long as the relationship isn't so far off to make the wrong spark plug fire )

Not possible. The cam would be so far out of spec you would bend all the intake valves first. Ask me how I know

[the commissar!]

98t5M, on 03 January 2012 - 10:32 PM, said:

I thought the cams have 7.5deg of adjustment each direction for a total of 15deg, which works out to 30 degrees of crank rotation

You are correct it is a potential adjustment of 30* not 7.5* crank degrees, I had my ratio backwards...