Nissan CAS – Facts and Fiction
The Hot Debate
In this article we will attempt to separate facts from fallacies, explain the cause of the problem and recommend a solution that could not only save you costly repairs but help you make the most out of your RB engine.
How Nissan’s CAS Works
Nissan’s RB CAS is an optical sensor located on the exhaust camshaft gear. Its job is to read both the engine speed and the piston/stroke position and relay that information to the ECU which then uses it to calculate and deliver Fuel and Ignition events.
Potential Problems
The main shortcoming of this system is its reliance on the single CAS to measure both engine speed and engine position. Because the camshaft is linked to the crank via a timing belt, any distortion in the timing belt will result in an inaccurate crank angle position being delivered to the ECU.
When inaccurate data is then sent to the ECU, it will make ignition and fuel calculations based on that inaccurate data and as a result the injector and ignition timing accuracy will be compromised.
Just how much timing belt deflection can you expect on an RB engine? On a stock, unmodified engine it may be barely noticeable but once you start adding mods and increasing power levels, the belt deflection will increase dramatically. We have seen up to 8 degrees of cam belt deflection in 700kW RBs. That’s quite a lot!
The solution
Fortunately there’s a simple solution to this problem and that is to replace the OEM CAS with a cam and crank sensor kit.
How does this help with the belt deflection issue? By splitting the OEM CAS into two separate units, the cam shaft sensor is used solely as a home signal with the crank position sensor providing the cylinder/stroke information. Aligning the cam signal with a gap between the teeth on the crank gear allows plenty of room for the belt deflection and effectively eliminates any negative effects caused by it.
Is it only applicable for high horsepower cars?
While the belt deflection certainly has a greater effect on modified, high power engines, fitting a crank angle sensor kit to low and moderate power RBs will still pay dividends with more reliable, accurate signal and thus a better, more efficient tune.
Matching your sensors to your gears
It’s important to choose a correct sensor for your cam and crank gears. Your decision on using a Reluctor type or a Hall Effect type sensor will depend on the number of teeth on the cam or crank gears.
Further Reading
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