What timing?

[JimX]

Should I be using the standard 15 degrees for best economy? At the moment I'm after optimal economy rather than optimal power, as I'm going on a long trip up north over Christmas. This is just a temporary measure until I get the PowerFC tuned early next year, I just want to save some bucks on fuel until then.

[WazR32GTSt]

more power at lower rpm = car rums at lower engine speeds and thus saves on petrol. would this be right?

thus assuming you have the boost turned down then any extra power would only help the economy of the car as it will run al lower revs...

this is just from my reasoning and could be completely wrong, ut using this logic i say up the timing to around 20deg btdc

[blind_elk]

Optimal power = optimal economy, because the engine is running at its most efficient. Therefore, base timing should be the same, ie 15 BTDC.

[JimX]

Thanks for the info guys. Ok here's another question - how accurate is PowerFC at gauging the timing? I notice that whatever it's set to, it tends to fluctuate upwards, up to 2 degrees or so. So even though it's at 15 at the moment, it occasionally spikes up to 16 or 17. This is all at idle of course.

I'm going to check it with the timing light anyway soon, I'm just asking this in case my cheapass timing light doesn't work with the wire loop at the back of the engine (as many of them don't).

Btw, I can't recall any difference in power when the timing was at 20 degrees (compared to the 15 it is now) after I put the CAS back on. Although maybe I just didn't hammer it hard enough, I don't know.

[raist60]

The PowerFC doesnt gauge timing at all. Its telling you what your timing SHOULD be, not what it is.

And most timing lights will work ok they just end up being double what it really is. Ie. 30 degs is actually 15.

[JimX]

How does it figure out what it "should" be? I'll check it with the light tonight.

[blind_elk]

How does it figure out what it "should" be? I'll check it with the light tonight.

Same as any other ECU does - it has tables of data built in, which tell it what ignition timing should be based on certain inputs like load (MAP or AFM), throttle, engine temp, rpm.

The PFC will be displaying the actual timing it is running. The figure will vary slightly at idle because the inputs will be varying slightly, and the PFC will be calculating a 'best-fit' result between the values it has in its tables and what is actually occurring. eg the engine is probably idling at 700, but the PFC only has values for 500 and 1000, so it guesses what the probable value is for 700.

[JimX]

Ok now I'm confused. One person says the PowerFC doesn't show timing, and another says that it does.

Anyone else want to throw their vote in?

[blind_elk]

Look at it this way - if it doesn't show you what timing it is actually applying, how the fu(k do you set it? (you can't get out there with a timing light when you're cruising down the Hume at 110 kph, now, can you??)

[JimX]

It could just be a relative thing. Like it will assume the timing is X degrees, and base all of its subsequent measurements off that.

I'm not disagreeing with you, I too think that it gives you a proper reading. I'm just saying how it might not be.

[Steve]

Base timing is set off the CAS.

Power fc tells you where the ignition timing is set for a particular map cell, so as revs change, even slightly, the timing may change, depending on where it is set.

Without being able to vary ignition timing, the power fc would be little more than a fancy SAFC.

[JimX]

So when I set the timing via a timing light to 15 degrees, what should the PowerFC be reading? 15 degrees also? And at what RPM should I set the idle timing? Mine has been fluctuating for awhile, it seems to go between 750 and 1000rpm, though these past few days it's been hovering at around 850.

[Steve]

Jim, I believe the timing is set at 660rpm for a stock R33.

If your revs are jumping, try putting a screw in the PCV valve - it fixed mine (which I had been trying to sort for bloody months) and see if that helps. Otherwise, if you still have the stock ecu, plug it in, set timing and then plug in the Power fc.

I am not 100% what the power fc will be reading, it gets its signal (AFAIK) off the CAS. If it is still in base (untuned) map, it should be fine. I drove for weeks on untuned power fc, and had good economy (around 10L/100km).

Perhaps the power fc sees works on 15deg off the CAS and then adjusts up and down from there. Whenever I have had my car tuned they will always check the base timing. From there the Power fc can vary up or down as needed, so I suppose what it reports is only relative to where the CAS is set. If that makes sense?

[JimX]

Well the revs seemed to be holding at 850 or so, so I set the timing there. At first I thought it was 30 degrees according to the light, but then I remembered Raist's comment about most lights reading double. It was spot on the last mark (30 degrees on mine, I have 7 marks) and didn't fluctuate at all. Unlike every other car I've had!

I think when my idle was screwy the timing was 20 degrees, it might have been related to that. Now it seems to slow down to around 950 then drop down to 850 after a few seconds.