quote:

Originally posted by anony00gt:

**OK guys, here we go.**

What is the max amount of boost the stock turbos can make?

How much boost can the engine internals take?

How much boost can the stock fuel system support?

How many people know someone who has done more to an S80 T6 than IPD's ECU upgrade? Got details?

That is all...for now...I think. Thanks.

Spoken like someone who has no idea what an S-N diagram looks like and its significance.

First let me ask, how long do you want the engine to last? A minute? An hour? 10 years/200,000 miles?

Volvo prides itself in long-lived cars, so their answer is over 20 years, hence, they'd design the engine for 'infinite fatigue life'

**The long story:**
Bump up the power and you'll just break something sooner. You can figure this out by the material used and the expected stress you put on it. Let's take the piston con-rod, for example. At 6000 rpm and max torque it's seeing peak force 3000 times a minute, or 500 times a second, up to peak force and then back to zero or even negative (tension stress) as the crank is yanking the piston down on the intake stroke.

These forces impart stresses into the con rod. You want the rod to be thin and light for max engine performance. Trouble is, the thinner the rod, the higher the stresses. The higher the stresses are, the more likely you'll fatigue the part.

OK, this is where the S-N curve fits in. If you plot Stress (S) on the ordinate and N (number of cycles) on the abscissa, the curve looks pretty much like a plot of 1/N + C where C is a constant and N is the value of the horizontal, or x, component (in this case total number of cycles). If stresses remain below the line for the given number of cycles the part won't break. If the number of cycles for a given stress intersects the curve, then the part will break. Now because the curve pretty much has the form of 1/N + C , if you keep the overall stresses below C then the part will have 'infinite fatigue life.'

If you raise the boost you'll raise the force on the con rod, thereby increasing its internal stresses.

*If you raise the forces above the critical point you'll then expect con rod failure at the number of cycles corresponding to the stress level.*
Note that N is the cumulative number of cycles. At 500 cycles per second, it doesn't take long to build up N to a million cycles.

So, boost all you want, but don't expect the engine to last. If you overboost too much you can get the fatigue life down to a few

*minutes* and punch the con rod through the cylinder wall.

Overboosting also increases turbine temperatures which cause the turbine blade material to 'creep' at a faster rate, (i.e. stretch) as it's spinning at 20,000 rpm. Once the turbine blade impacts the housing wall at 20,000 rpm the turbo effectiveness will decrease dramatically as the turbine self-destructs. The factory determines allowable turbine inlet temperatures even in worst case desert conditions such that the creep is kept to a low level to maximize lifetime.

The factory pretty much determines how long it wants the parts to last, determines the number of cycles and the stresses allowed in the parts such that you'll have a good operational lifetime with the car. Bump up the boost and things won't last as long.

I know this doesn't answer the question, but I couldn't resist . . . .