PhantomGT said:
I just watched a Mitsubishi Eclipse commercial on TV and this new Eclipse comes with a 3.8L 260 HP V6 with a 6-speed transmission. Now our cars come with a 300 HP 4.6L V8 with a clunky 5-speed out from the Old Testament. So at what point will these Ford Engineers drop a 6-speed into this car, because this car really needs one! Even the Nissan Sentra has a 6-speed option and
Brembo’s!
Personally I'm not sold on this more gears is better theory.
It depends what you want from a car. If you had the current box and added a 6th it would work like an OD giving really good cruising mpg at low engine rpms, but it wouldn't really help in accelaration. This is exactly what the Corvettes and Fbody's face. Unless producing massive BHP their top speed will nearly always be in 5th NOT 6th as they just don't have the power to pull 6th at high speeds.
The other option would be to close all the the other ratio's up. So 6th could have the exact same ratio as your current 5th.
This in theory would allow better in gear accelartion but at a cost of a lower terminal speed in each gear. Another down side is that you would have to change gear more often and changing gear means not accelarating and costing time.
And modern diesels and revvy 4 or 6 cylinder engines with a narrow power band 6 speeds help keep the engine on the boil. A grunty V8 like the Mustang does not need it as it has a much broader powerband.
Take a look at the new TVR Sagris, it will do
0-60mph in 3.5 seconds
0-100mph in 8.7 seconds
0-150mph in 20.0 seconds
and top speed in excess of 180mph
It will do 60mph in 1st and over 100mph in 2nd. It only has 5 gears.
The new Z06 is probably similar, I know it is geared to do 60mph in 1st, so most of its performance and probably top speed will be with 5 gears and 6th will be an OD for mpg crusing. Which is very handy but not essential.
There are some C6 owners claiming 29+mpg @ 70mph on the highway with the a/c on. - a real bonus of the long legged 6th gear.
If top speed is not needed a good old 4 speed gearbox is about bang on, but for a fast car it will normally limit your top speed to 110-120mph and crusing mpg will be non existant.
It's also worth noting that many modern 5 speed boxs run the same ratio's as a 4 speeder with an OD for 5th.
A 4 speed box would usually have 1:1 4th gear, a 5 speeder will usually retain that ratio for 4th (hence dyno runs should be done in 4th) but 5th will be 0.xx:1 ratio.
Modern sequential boxes can change gear very fast such as the new 7 speed box in the new BMW M5, but they have other drawbacks for street use. Auto's can also shift much quicker than a manual can and could benefit from more gears like the 5 speed ZF box in the Jaguar XK8, this was added as an OD however top speed is still in 4th. Too many gears in an auto an it will loose some of its refinment and be constantly shifting. My 3 speed XJS is very smooth and hardly ever changes gear, the downside is slightly more lack luster accelaration.
Having driven a few 6 speed cars with close gearing you'll notice another downer. You seem to spend your entire time shifting, your right arm (for LHD cars) will spend more time on the gearstick than on the steering wheel. As each gear will have a very limited speed range compare to a normal 5 speed.
Personally I love the V8 grunt and love just crusing in my TR7 where I can leave it in 4th most of the time, with the knowledge that it will pull from 20-105mph no problem and still be faster than 80+% of the cars on the road.
However each to his/her own. If the alure of a 6 speed appeals there is no reason you can't fit one after market.