GTR R32 very unstable RPM reading especially at higher RPMs

[MGV101]

Running a R32 on stock Nissan 360 Opto triggers, all trigger settings as per the provided base map. Signal from trigger scope looks clean, no trigger errors.

The RPM reading is jumping all over the place especially at higher RPMs, the inaccurate RPM also seems to be causing unstable ignition timing. When calibrating the base timing, the rpm/ignition was stable enough for me to dial in the offset at idle but once I increase the RPM to dial in the delay (around 3000-4000rpm), the timing was fluctuating so wildly that I cannot properly read the timing mark at the crank pulley.

Due to the inconsistent/inaccurate ignition timing, I am only running at around 4-6 degrees advance at 1 bar of boost before I get knock.

Are the 360 teeth just to much for the ECU to process or is there something else wrong?

 

 

[MGV101]

I'll do a trigger scope at higher RPM tomorrow if needed but here is one done while cranking when I was trying to figure out why the engine won't start when I had the wrong jumpers configured.

Well, it won't let me upload anymore files due to the tiny file size limit per thread so here's a link:

https://drive.google.com/file/d/1BYUwCxZTyGGHIAthCt0NxVWlSKir74ln/view?usp=sharing

[Adamw]

Its pretty common on RB's.  Usually a combination of valve train resonance and backlash in the drive system.  First things to check is cam belt tension, replace the oring on the CAS shaft, check splines are a tight fit, check the male spline is still tight in the camshaft (they are pressed in and can come loose).  I have seen a good improvement in some with worn splines by filling the spline with sikaflex before assembly.  In some cases with bigger cams and/or valve springs the cambelt can get a fair bit of whip in it at specific RPM's also.  

A low cost "fix" that most tuners use over here is the NZ wiring cam trigger kit.   Although it is still mounted on the cam so not as good as a proper crank trigger they are a 15min fit and a very good improvement for the cost. Being cam mounted they are still exposed to the "cambelt whip", but the trigger wheel bolts directly to the cam sprocket so all other drive backlash is removed.  Because of a lower tooth count the ecu "sees" less effect from the cambelt whip than it does from the 360 slots.  The downside of this system is longer cranking for start up.  https://www.nzwiring.com/index.php/product/trigger-kit/

 

[MGV101]

Thank you Adam, so other than "Because of a lower tooth count the ecu "sees" less effect from the cambelt whip than it does from the 360 slots.", the 360 teeth isn't really too much trouble for the ECU to handle and swapping in a 24 tooth disk would have a minimal effect for improvement?

This is way way worse than other cam/distributor based trigger system I have seen.

Also should I turn on RPM filtering? Or would that create other problems on fast RPM changes?

[Adamw]

6 hours ago, MGV101 said:

Thank you Adam, so other than "Because of a lower tooth count the ecu "sees" less effect from the cambelt whip than it does from the 360 slots.", the 360 teeth isn't really too much trouble for the ECU to handle and swapping in a 24 tooth disk would have a minimal effect for improvement?

Processing the 360 teeth isnt an issue, just if the disc moves backwards and forwards more than 1 deg the ecu can see that movement.  If you have 24 teeth there is 15deg between teeth so the cam can bounce around a bit without the ECU seeing it.  The 24T discs that fit in the stock CAS usually do give some improvement, but not as good as the NZ wiring type kit.  You still have spline backlash and several other issues such as an optical sensor with 30year old optical lenses etc.  The stock CAS also shorts sensor ground to the block through the mounting bolts so in some cases that adds extra noise into the system too.  

 

6 hours ago, MGV101 said:

Also should I turn on RPM filtering? Or would that create other problems on fast RPM changes?

The RPM filter will smooth out your logged RPM value and also the RPM value that is used for lookup on the fuel & ign tables.  ie your active cell in the ign table wont be bouncing around as much.  But Ign timing is still always calculated based on real reported crank position so the RPM filter will not fix much of the spark scatter if it is due to the trigger bouncing around.