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I have an rb26 that I'm tuning and I notice that in the data logs the engine rpm fluctuates plus or minus 150-200 rpm from point to point (which is milliseconds). In my case this is a link ecu with a stock CAS. The tach reads normals and the engine doesn't seem to have any issues due to this but it seems excessive as currently I'm working through the VE table and I'm using a range of points to tune particular cells. Is this typical? or should I look into something? I also notice that it seems to prematurely hit the rev limit by a few hundred rpm which I attribute to this issue. Any tips or ideas are appreciated.
The Nissan CAS is well known for creating problems which will show up as erratic rpm. It can also create timing and fuelling inconsistencies which make it hard to tune the engine accurately. This is usually only mild in a stock engine but gets much worse if you've got an engine with a more aggressive cam profile. The premature rev limit may be a result of inconsistent rpm input, however the Link rev limit actually starts to soft cut by the limit range (typically 200 rpm) before you get to the limit value you've set. The same happens with the MAP limit.
The ultimate solution is a crank trigger system however that's an expensive upgrade. An NZ company called NZ Wiring makes a trigger kit that replaces the stock CAS and we've found it to be a huge upgrade over stock without the expense of a crank trigger. I personally won't tune an RB26 with the stock CAS any more.
Dang well that seems to answer it.I wonder if its the Cas itself or the mechanics of the engine that causes trouble? Its odd that similar encoders in industrial usages dont yield these issues. For the money it seems that the trigger kit is worth it. Live and learn
There's a few issues here: First up is the high tooth count of the stock CAS (360 slots for engine speed). This is then combined with the natural harmonics/whip that is placed into the cambelt by the valve train.
I was researching/ toying around with the settings and I will say that using "low res" mode and a 2 rotation filter cleaned up the signal significantly.But I am after a solution better than that.
Are there any advantages/disadvantages to using a 24-1 cas rotor compared to the NZ wiring kit? I'm thinking that one of those with a little signal filtering will get me where I want to be with this engine.