This is what I dont get: how does going super rich protect the turbos
Let's talk a little bit about EGT in an engine, look at how the engine operates from factory and why LAMBTS is used to protect the turbos.
EGT is highly dependent on two things - spark timing and air fuel ratio.
Stock, the car spends most of it's operating time at Lambda=1, to produce the least possible emissions.
As it happens, peak EGT also occurs at lambda=1.
I already talked about flame front speed before. A faster burn while maintaining the same ignition timing is pretty much equivalent to advancing timing.
LAMBTS in a stock RS4 tune enriches roughly to lean best torque or 13.3.
This enrichment has the following consequences:
1. The flame speed increases (same as advancing timing a little)
2. We get further away from EGT peak (going both leaner and richer than 14.7 gives you lower EGT's, but richer is more effective).
3. We also can further advance timing because the additional fuel provides a cooling effect for the cylinder inhibiting knock.
4. Cooling the cylinder charge with additional fuel also means cooler combustion.
So, the way it is implemented stock, it is incredibly effective at lowering EGT when compared to operating at Lambda=1.
Think how the ECU is calibrated from factory. Emissions are king, so it is calibrated for Lambda = 1, thus what it does with BTS is protecting the turbos first and foremost.
