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Old 04-08-2013, 07:43 PM   #9
Derbagger
Scooby Specialist
 
Member#: 32113
Join Date: Jan 2003
Chapter/Region: NESIC
Location: Trollhatten, Japan
Vehicle:
05 Saabaru
Satin Grey

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Quote:
Originally Posted by HipToBeSquare View Post
It always strikes me that in order to get higher miles per gallon, they try to employ turbochargers, which by definition, pressurize the engine, requiring and allowing more fuel to be burned.

They arrange mpg tests to maximize low-load driving cycles, (usually when turbos are not spooled) to make the numbers look good, then when people normally drive, and actually USE the throttle, observed fuel economy isn't what the 'official' ratings promised.

Direct injection helps to not require pig-rich mixtures, like EJ Subaru turbos use, to avoid detonation, and also allow the use of higher static compression ratios, which help an engine run more like a good atmospheric engine when the turbo isn't pressurizing the intake above ambient air pressure, but it isn't flouting the laws of chemistry or thermodynamics. Energy out requires that energy to be put in first, which is stored in the fuel, not in the air.

As much as I like the rush of turbos, there is still something sublime about a well tuned, responsive, atmospheric engine, and Porsche builds some beauties.

C'mon... 991 GT3-RS is rumored to make ~450-460-475 naturally aspirated horsepower out of 3.8-4 liters, on an M97-derived block, not the previous metzger block, which had it's sunset with the 997 GT3-RS 4.0 this last year.

The far side of 450 naturally aspirated horsepower out of 3.8 liters... that is amazing stuff.
You are right, as the direct injection allows a more efficient off-boost compression ratio, but it's more to hit an EPA number. It an everyday car, I actually like that. The idea that I could putter on my commute, then blast around when I want to (saving gas when I need to drive and burn it all who cares when it's for pleasure). But for a Porsche a N/A motor is more enjoyable.

The two things I want to point out are, that when a motor is tuned for high revs, it's often lower on torque, causing you to need to rev it to make useful power(the same problem you get with off boost power). and the higher revs bring greater friction, reducing efficiency. Now, I agree that sporty cars could be better off with that setup, but the current one-size-fits-all EPA lends itself to the small motor/turbo programs so many use today.
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