Quote:
Originally Posted by Ryephile
Maybe, but not always, and FWIW I hadn't considered money within my proposal. I'm not sure why small turbines make you cringe; there's a time and place for most things and I know you're intelligent enough to understand that. If we're "only" talking a 270HP solution, why would you mis-specify a turbo that's "good for" 350HP?
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I guess I didn't put it very well, and maybe cringe is an overstatement.
The turbo's natural habitat is boosting the engine's maximum power, because the turbine does the best job of collecting waste energy when it is free flowing. If you throw response out the window, pretty good thermal efficiency gains can be had too. "Small" is relative, and in principle a "small" turbine paired with a very free flowing housing and the right compressor can give a very efficient 270hp setup.
What makes me dislike turbos is that dyno queens aside, this typically isn't what people want to use a turbo for. First of all if you want response, any turbo is by default giving up a few hundred milliseconds or more of transient response time. A turbo that makes a whole lot of boost at low-mid engine speeds is by default restricting the top end, whether or not the torque is falling off or not. It *is* reducing efficiency. Then it gets worse, because some people decide they need more boost in the previously deficient places in the powerband, and then they use a wastegate to vent off some pressure and stop the engine from blowing up. And as you know, typical aftermarket wastegate is not electronically controlled.
At this point, you have the same powerband as a positive displacement supercharger at less cost, but the transient response is worse, there is more piping, the turbo is wasting some energy during daily driving, and you've thrown away efficiency everywhere except at low engine speed where the turbo starts to produce some boost (and this is only at maximum load obviously). Doesn't a Roots blower seem much more elegant to you? Less valves, less piping, better response (probably easier to tune I imagine), and comparable or better efficiency, depending on which blower is being used. The only place it's less efficient is when you stomp on the gas pedal at low rpm, which isn't really good for the engine anyways.