Ignition timing erron in next cylider mode?

[keithmac]

I`m running ms1 v2.2 029Q2 in Distributor mode, car sees 7000 rpm tops.

When flooring the throttle in high gears the car will knock/ping although in 2nd/maybe 3rd I can use more ignition advance before it knocks?.

I`ve heard timing errors of 6 degrees or more being banded about for next cylinder mode, how do you work the timing error out for a specific install? I`m running off a 4 window distributor, hall sensor.

I`m on the limit of next cylinder mode with my setup, trigger angle of 0, would it be a lot better to re-wire the ignition so the trigger angle is 5 degrees above my maximum advance?, would I get a lot more precise ignition timing this way?.

I`ve read other manufacturers use an ignition timing adder based on RPM acceleration, I was thinking of the same for my install using rpmDot but if I`ve already got 6 degrees of error because I`m in next cylinder mode I`d like to sort that out first, then use this for low load compensation or similar.

Any thoughts or comments welcome

[PSIG]

... When flooring the throttle in high gears the car will knock/ping although in 2nd/maybe 3rd I can use more ignition advance before it knocks?. ...

Not to ignore your primary question, but you may be seeing additional load, air, and cylinder heating by the time you hit high gear. You can test for this various ways, such as easy accel to high gear then full power. If there's less or later det then it's cylinder (head, piston valves, etc.) heat rather than strictly timing.

The additional load is obvious, and the increased IAT due to intake system heating will register on the IAT sensor, so any more heat in the cylinder will take it over the edge.

You may also wish to try retard based on IAT. Push your timing (to max torque) then program some relief with retard once the IAT gets hotter than you see in the lower gears.

I'll leave the specific next-cylinder issue to others.

Hope that helps,
David

[keithmac]

Cheers for the input, I`ve been pondering over retarding spark using IAT, but the car does it from relatively cold as well, no real heat in the inlet manifold or intake charge. 8dbtdc seems to be the magical number under full load and low revs, maybe it`s just a quirk of the engine setup I have?

[jsmcortina]

would it be a lot better to re-wire the ignition so the trigger angle is 5 degrees above my maximum advance?, would I get a lot more precise ignition timing this way?.

The code already does prediction based on engine to aim for correct timing, but next-cylinder can never be as reliable as this-cylinder or a full toothed wheel solution.

If you can re-wire your dizzy for this-cyl with trigger return then you will be less reliant on the code prediction and may get more stable spark. i.e. without strobing it you do not know what the existing error is.

The pinging under load in high gear sounds more like a tuning issue than a code one. There have been other reports that engines can stand more advance in low gears which does make some sense as the engine has less load on it.

James

[KariM]

I`ve heard timing errors of 6 degrees or more being banded about for next cylinder mode,

Where is this info from?

I'll check this tonight with my strobe, I have 0, 20 and 44° marks on my pulley and using next-cyl. I'm quite confident the timing is dead on in static situation, but let's see.

[keithmac]

KariM, it was in a discussion on here a while back. If you could set the fixed angle to 20 dbtdc and check the timing marks at differing rpms, also a slow rev increase and then a fast rev increase it would be interesing to hear what you find.

I may check mine at the weekend as well, I have to remove a fair bit of suff to see the flywheel markers though, but these are the most reliable timing points on my engine.

If it turns out not to be a big problem I`ll leave it and look into the advance adder based on rpmDot, I`d just like to clear this up first.

[KariM]

Ok, tried, but did not succeed to clear this completely.

I set up the fixed angle to my timing marks (tried all three), and up to 2500rpm no noticeable error, neither in static, accelerating or decelerating rpm. My trigger angle is 8°.

After that point my loose triggering (hall in dizzy which is driven by cam chain and anglegear) starts resonating and spark bounces randomly some degrees. This happens with stock ecu too. Unfortunately this renders the test pointless in higher rpm's.

I should definitely move the triggering to crank. Before that, I'm wondering if I'd better to disable the advance prediction, as I assume it goes nuts when the trigger bounces around.