Quote:
Originally Posted by JohnnyGrey
If you could vary that intake cam on the fly, I could see your point, but why would you want 2.5L worth of metal moving around in a motor that breathes like a 1.8L? So the turbo brings you back up to stock horsepower? Also remember that turbo energy isn't entirely free. That backpressure costs you.
|
1.) Increased fuel economy
2.) A custom cam is much easier to source then a custom 1.8l engine
Mazda downsized their Millenia engine partially for reduced friction, but they were
designing a new engine. My point is that a turbo
can increase a full sized engine's fuel economy. Whether it is desirable or not is an individual's choice.
Fuel efficiency had to come from somewhere. A turbo takes energy, but it takes less energy then the piston to accomplish the same job.
Quote:
|
Originally Posted by JohnnyGrey
The manifold AT ambient decreases pumping losses and any engine can do this perfectly well without a turbo. It's called flooring the accelerator. The problem, like I've stated many times in this thread, is that I have no way of efficiently using that power. The way a turbo can help, is if I downsize my 2.2 to something like a 1.2T. That way, I can run that 1.2L at atmospheric manifold pressure while cruising, well within the BSFC sweet spot. The only reason that turbo is necessary, is to make the little 1.2L viable for when I need to pass or merge into traffic. During FE cruising, it lies dormant. If I run my 2.2L at atmospheric manifold pressures (with turbo or without), I'll be over 100mph before long.
|
I understand the function of a downsized-turbocharged engine, but what I don't understand is the variation of pressure with throttle position (assuming constant boost).
Obviously when the turbo isn't producing boost, the engine is essentially N/A, but what about when the turbo is working? I think a turbocharged engine running at part throttle will have an above ambient intake manifold simply because airplanes seem to do it all the time.
A conventional turbocharged engine, which will not require boost at cruise, will not eliminate pumping losses. A Miller-cycle engine, which will require some boost at cruise, should eliminate pumping losses. Therefore, a turbo
can eliminate pumping losses...right?
- LostCause