Not to deter from the discussion, but I'd like to learn something here. The system, wether with or without cat, depends on the speed of the turbo's building pressure at various throttle openings/load. The biggest influence on the spooling is the density and speed of the exhaust gasses, and the pressure difference between pre- and aft turbo intake air. Am I correct so far? The 'signsl' to the wastegate is governed by a solenoid valve that is itself governed by the 1-4 cylinder ECU. Now if we change the back pressure, and with that the density and speed of the exhaust, the spooling goes off the chart of what the ECU is capable of geverning the solenoid regulator valve, OR the applied waste-gate can't handle the pressure difference, OR a combination of both? What I can't see in this is, apart from pressure leak on the turbo exhaust side, the exhaust volume doesn't change under a given load, the same amount of air and petrol are being used to produce a certain amount of power. Then why isn't the sytem capable of handling the change of exhaust system after the turbo's/wastegate?
I told you-it is the RATE of the rate of change-in multivariate calculus...this is in the 6th semester of University Mathematics It seems you seek a simplistic solution for an extremely complex set of variables-if it was soo easy, everyone would be doing it-right?
I am not seeking a simplistic solution, I'm just trying to get to grips with what happens physically in order to understand WHY it happens. Do you have the mapping (there may be several different versions?) available to you? Would you be able to simulate what is happening with the inputs to the ECU to create the occurrence? It would certainly help (me, if nobody else) if it could be made visible in some diagrams.
The OE turbo was specifically tailored to the system: hence specific to flow rate. An IC engine operates on mass flow rate. A carburetor for example operates on volume flow rate. Big difference in design/ operation. Reduced exhaust system pressure equals turbines spinning out of it's designed efficient range (not to mention associated bearings) because of change in flow rate (not that the volume of air has changed, the rate has changed and in colder weather the density has changed too). Over speed the turbos enough and failure results. Seen it many times. So, reduce exhaust pressure, change other system components to take advantage of the change. Note the word 'system', that's what it's all about, one alteration effects other components. Here's a nice tutorial from Garrett: http://www.turbobygarrett.com/turbobygarrett/tech_center/tech_center.html Best, Rob
Thanks Rob. I didn't think that changing the exhaust system AFTER the turbo would have an influence, but aparently it does. Thinking back now it is actually quite logical. Did the original posters problem ever get solved?
Don't know about the history of that issue, such an old thread. Here's the take-away, as an engineer we're trained to always look at the 'total system'. When modifying an engineered system (and a car is about as complex as a mass manufactured item gets) keep this perspective in mind: total system. Good discussion! Best, Rob
