[Taskmaster]

Why do you guys lose so much power (or rather, make peak power) below the 7000rpm redline?

And when do you shift?

[135Pats]

Originally Posted by TheAxiom

Why do you guys lose so much power (or rather, make peak power) below the 7000rpm redline?

And when do you shift?

Stock frame turbos operate in a very crowded space, put simply they’re just very small. As a result, heat and backpressure build up quickly. You just can’t move enough air up top to hold the power curve to redline on stock compressor and turbine wheels. If you really wanted to you could boost whatever let’s call it 20PSI approaching redline. You’d hold some of the power…you’d also smoke the turbos in no time.

Stock frames you will always have that fall up top. N55 curves are even more severe.


I shift at 6K even

[Jeff@TopGearSolutions]

Stock turbo's were designed for peak torque at a very low RPM. Because of that the power tapers off near redline.

There is always a give and take.

I usually shifted at redline first, 6500 RPM 2nd, 3rd and up at around 6200 RPM.

[Jewber]

With small turbos, you can pump a lot more air in the middle of the rpm range than you could on a n/a engine which is why the power drops off sharper.

Even in your n52 dyno the torque starts to drop off at 5000 rpm due to increasing friction and worse VE as rpms increase.

[Taskmaster]

Ahh, I figured it was the stock turbo's limits or problems with headflow which kept the power down in the higher RPM.

[deadlyrhythm]

Nature of the beast for centrifugal compressors. They use velocity to generate pressure, and there is a curve at which they're designed for. They selected that RPM level for peak performance/ upper operating mode, likely to match an RPM range for the engine. 7xxx rpm is probably the upper echelon for the engine but the turbo is maxed out before that and is falling off its curve at that point.

You can always change the turbo wheel, size, amount, etc but with it always comes a different change in operating mode.