High speed fuel economy
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High speed fuel economy
Driving home at a high speed cruise last night, I was pondering, not for the first time, what would be the most fuel efficient car in the world, at a proper high speed cruise?
I reckon the LC would get something in the region of 21mpg (US) at a constant 100mph, on the flat. At that sort of speed, weight is much less of a factor than the drag coefficient, the frontal area, the gearing and of course the efficiency of the engine under the required load and RPM.
So you ideally want something small, aerodynamic, with a reasonably large NA engine and long gearing, though there might be a very large-engined diesel contender. I always found my old Porsche 993 to be surprisingly efficient at autobahn speeds - at 120mph it seemed to drink less fuel than my BMW 335d.
I reckon that at 100+mph, the LC V8 is a contender (the hybrid would not be, over a meaningful distance, as it has shorter gearing, the hybrid system would be fully discharged and the V6 would be straining to keep up, relatively speaking). Others might include a Porsche Cayman with the 4.0 engine (legendarily long gears) and an early 90s Corvette ZR1, again with stratospheric gear ratios and that quad cam Lotus V8.
Thoughts, anyone?
I reckon the LC would get something in the region of 21mpg (US) at a constant 100mph, on the flat. At that sort of speed, weight is much less of a factor than the drag coefficient, the frontal area, the gearing and of course the efficiency of the engine under the required load and RPM.
So you ideally want something small, aerodynamic, with a reasonably large NA engine and long gearing, though there might be a very large-engined diesel contender. I always found my old Porsche 993 to be surprisingly efficient at autobahn speeds - at 120mph it seemed to drink less fuel than my BMW 335d.
I reckon that at 100+mph, the LC V8 is a contender (the hybrid would not be, over a meaningful distance, as it has shorter gearing, the hybrid system would be fully discharged and the V6 would be straining to keep up, relatively speaking). Others might include a Porsche Cayman with the 4.0 engine (legendarily long gears) and an early 90s Corvette ZR1, again with stratospheric gear ratios and that quad cam Lotus V8.
Thoughts, anyone?
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Joined: Oct 2022
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From: California
Driving home at a high speed cruise last night, I was pondering, not for the first time, what would be the most fuel efficient car in the world, at a proper high speed cruise?
I reckon the LC would get something in the region of 21mpg (US) at a constant 100mph, on the flat. At that sort of speed, weight is much less of a factor than the drag coefficient, the frontal area, the gearing and of course the efficiency of the engine under the required load and RPM.
So you ideally want something small, aerodynamic, with a reasonably large NA engine and long gearing, though there might be a very large-engined diesel contender. I always found my old Porsche 993 to be surprisingly efficient at autobahn speeds - at 120mph it seemed to drink less fuel than my BMW 335d.
I reckon that at 100+mph, the LC V8 is a contender (the hybrid would not be, over a meaningful distance, as it has shorter gearing, the hybrid system would be fully discharged and the V6 would be straining to keep up, relatively speaking). Others might include a Porsche Cayman with the 4.0 engine (legendarily long gears) and an early 90s Corvette ZR1, again with stratospheric gear ratios and that quad cam Lotus V8.
Thoughts, anyone?
I reckon the LC would get something in the region of 21mpg (US) at a constant 100mph, on the flat. At that sort of speed, weight is much less of a factor than the drag coefficient, the frontal area, the gearing and of course the efficiency of the engine under the required load and RPM.
So you ideally want something small, aerodynamic, with a reasonably large NA engine and long gearing, though there might be a very large-engined diesel contender. I always found my old Porsche 993 to be surprisingly efficient at autobahn speeds - at 120mph it seemed to drink less fuel than my BMW 335d.
I reckon that at 100+mph, the LC V8 is a contender (the hybrid would not be, over a meaningful distance, as it has shorter gearing, the hybrid system would be fully discharged and the V6 would be straining to keep up, relatively speaking). Others might include a Porsche Cayman with the 4.0 engine (legendarily long gears) and an early 90s Corvette ZR1, again with stratospheric gear ratios and that quad cam Lotus V8.
Thoughts, anyone?
Thread Starter
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At 100mph, the LC does get ~20-21 mpg. I drive with the wing in its down position to lessen drag. My 2015 Golf TDI still easily exceeds 30mpg at that speed with mpg decreasing more steeply than the LC compared to 80mph. Would be interesting to know how close they are at 120mph, but I won't be the one finding out.
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From: Wis
Thread Starter
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Nice Porsche! I forget the figures - this was about 15 years ago - we drove in a high-speed convoy across most of Germany, and I remember the BMW took on slightly more fuel at each stop. I guess we were going fast enough that we were well into the big blower territory in its sequential turbo setup.
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In the LC once I was past the initial break-in, I got 26mpg with cruise control set at 85mph on the highway for several hours including some episodes of having to slow down then pedal-down to pass slower moving traffic. That is killer mpg for a 5 liter V8 without any cylinder deactivation nonsense.
Nice Porsche!
Nice Porsche!
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When I did a trip from Raleigh NC to Orlando Fl last summer, cruising at just under 80 mph, with one stop for gas filling, was able to see 31.4 mpg until traffic started slowing just 100 miles before destination. With crawling traffic for around 60+ miles, got just above 30 mpg for entire trip.
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From: mn
In the LC once I was past the initial break-in, I got 26mpg with cruise control set at 85mph on the highway for several hours including some episodes of having to slow down then pedal-down to pass slower moving traffic. That is killer mpg for a 5 liter V8 without any cylinder deactivation nonsense.
Nice Porsche!
Nice Porsche!
Last edited by theryanking; Feb 24, 2026 at 05:37 PM. Reason: *add detail
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