4G63 stock Ref/Sync setup timing accuracy

[Alex B]

Given that there is only 2 teeth on the crank trigger wheel there are
2 signal state changes (rising or falling) that ECU can use to sync
its timing what gives resolution of 180 degrees. Or ECU is
using different strategy for its timing?

Isn't it too coarse for high performance engine?

What is recommended crank/cam teeth count for
the high powered engine that can have large RPM changes
in short time period? Obviously the more the better
but there should be some practical limit that won't
improve accuracy much rather then introduce more
possible errors due to some valvetrain slack.

The reason for asking is that I am going to try different
trigger setup on one of the Evos and would like to hear
some opinions.

Regards
Alex

[RossB]

Basically if you have more teeth the ECU can calculate RPM more frequently. The ignition timing is always acurate but with more teeth the timing calculation will be more "up to date" on a setup with more teeth.
If you use a missing tooth mode (say a 36 - 2 trigger on the crank) the ammount of slack in the camshaft drive should not affect the acuracy of the timing.

[dzhingov]

What this is mean - the standart 2 teeth crank trigger wheel can be use without a problem for tuning tne car?

[RossB]

The standard trigger should work fine, I haven't heard of people having issues with it...

[Karel]

I have big start sync problem using AEM EMS. (reported from many other users on 4G63) Sync comes one sometimes after 1second, but next even 4seconds and you know, there is no fuel and spark without stat synced. I hope switching to Motec will solve my problem.

Another question: Does the ecu calculate cam advance/retard from the signal "drift" between cam and crank signals on evo 9?

[RossB]

The ECU cannot sync up instantly, it needs to see enough teeth from the ref and sync sensors so that it can acurately calculate the position of the engine before it delivers fuel and spark. This could take a couple of crankshaft revolutions.

In most instances we want an engine to fire up as soon as possible but I have tuned race engines in the past and deliberately prevented them from starting instantly from cold to allow some build up of oil pressure during the cranking period.

On the EVO 9 there is a sensor on both camshafts. The exhaust cam sensor is used for sync and the inlet cam sensor is used to calculate the position of the cam. This is calculated by comparing the position of the cam sensor relative to TDC.