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Old 10-28-2012, 12:22 PM   #21
lemming
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Quote:
Originally Posted by JST View Post
There's no direct comparison that I'm aware of. Closest might me something like a GT3, which is obviously a 6 rather than an 8. But no one gears their cars the way that GM gears the Vette, in part because the general bias in European cars seems to be final drives and top gears that put the engine closer to the meat of the powerband at cruising speeds.

The 7 speed in the new Carrera S has a cruising oriented top gear, but I don't have the time right now to look up the gearing and fuel economy numbers for that car (and even that one is down 2 cylinders and 70 hp on the new Corvette).
I would guess the new 911 S models could get 26mpg cruising at 75 --which shows how disproportionate the value of displacement would be in this discussion.

3.8L DOHC engine with amazing HP/L and any 6.2L or 7.0L v8.

Very different power deliveries, which speaks to the differences in how the engines breathe. But torque is always a function of physical engine size --so the DOHC engine's point in life is to bring the torque to higher in the rev band. But fuel efficiency (which itself is secondary in a sports car) suffers a lot.
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Old 10-28-2012, 02:11 PM   #22
John V
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The 26 mpg thing isn't really fair, though--that's in the Corvette, which is small, light, and (most importantly) has an interplanetary overdrive gear.

Put a 4.x liter DOHC V8 in a similar car with a similar OD and I don't know that the mileage would be any worse.
You get away with a massive overdrive when you have big displacement. BMW can't do that in the m3 because the v8 isn't nearly as torquey.

Engines run most efficiently at low rpm but high load and wide throttle openings. So a BMW 4 liter v8 turning lots of revs at freeway speeds gets worse mileage than a corvette 7 liter turning just above idle.
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Old 10-29-2012, 02:26 PM   #23
Rob
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The CTS V was big, heavy and fast. It got 25 on the highway always and sometimes more.
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