Quote:
MITCH : The Solstice 2.4 does need a 6 speed for sure. At 55MPH my revs are under 2,000 and I get 36.4 miles per gallon on the Highway.
If I bring the car up to 65MPH the revs go up to 2,500+ and I lose about 5 MPG. That's kinda sad.
My 08 Altima CVT 6 speed Automatic easily gets 38 MPG at 65 all day long. That extra gear brings down the revs big time.
G.M. could easily make the Solstice in a 6 speed, and it would help their overall MPG's
Just my
Mitch
Most of that difference in mileage is due to the aerodynamic losses at the higher vehicle speed, not to the higher engine speed.
Six speeds will not necessarily make a difference in fuel mileage at cruise, the important number is the transmission's ratio range. The AR-5 has a first gear ratio of 3.75 and a fifth of 0.73 for a range of 5.14. The T-56 has gearsets that offer a 2.97 first and 0.62 sixth or a 2.66 first and 0.50 sixth. The ratio ranges are 4.79 and 5.32 respectively. What do all the numbers mean ? It means that, in terms of improved fuel mileage, one version of the T-56 could help, but that the other would hurt. There may be some advantage during acceleration and at intermediate speeds, but neither of those is easily quantifiable.
First, if we want to keep the overall drivetrain ratio fairly close in first gear we would have to change the final drive to 5.5:1. I personally think that the 3.91 in the 2.4 is too low, and that the 3.73 that is in the turbo car would be more appropriate. Even if we wanted to use the equivalent of the 3.73 we would still have to change the final drive ratio to 5.3:1.
If we assume that 65 MPH occurs at 2500 RPM with the stock drivetrain, changing the final drive from 3.91 to 3.73 would drop it to 2385 for a 4.5% decrease. At equivalent first gear ratios, the T-56 would drop 65MPH to 2415 RPM for only a 3.4% decrease. Not much benefit from something that is more expensive and heavier, especially as the weight penalty is likely to cost fuel mileage.
There may be advantages to a 6-speed over a 5-speed, but fuel economy is not necessarily it. And since the 5-speed Solstice outperforms the 6-speed Miata, maybe performance isn't it either.