In article .com>, "laocmo" > wrote:
>I've recently acquired a 05 MazdaSpeed Turbo, 6-speed, a retirement
>gift for myself. Love it so far. It's been 40 years since as a single
>guy I drove a '64 Vette 4-speed. My driver for the last 13 years has
>been a 6-cyl '93 T-Bird auto transmission. Now the questions. At 60mph
>my Mazda is turning exactly 3000 rpm in 6th gear. My old T-Bird loafs
>along at 1750. Both have roughly the same hp. My 300 hp V-8 Corvette,
>with a 308 rear end turned about 2750 in 4th if I remember right.
>Anyone know a good source for the relationship between rpm, highway
>speed, horse power, number of gear speeds, etc. How can that old Ford
>engine cruise along at 1750 when it takes the MX-5 3000 rpm? Why do I
>need 6 gears in the Mazda when 4 worked fine in the Corvette? I
>probably knew all these answers 40 years ago, but I need a refresher.

I agree with everything Lanny said. But the simplest relationship
might be: smaller engine, higher rpm's.

Engine torque is pretty much proportional to displacement (not
considering force-induction engines which effectively multiplies
displacement). So to make the same power which equals torque*rpm,
they have to spin faster.

If all else is the same with a car (weight, size, etc, which
obviously it isn't here), it will take the same power to drive any
given combination of speed and road grade. Thus the smaller engine
must turn higher rpm.

Now, in your case, it is force-induction, and makes a fair amount of
torque. And its in a small car. So it should be able to be geared
longer and turn lower rpm than 3000 @ 60mph. Lanny is correct that
Mazda however chose to keep the rpms high in consideration of the
sporting nature of the car. Also, it helps mask turbo lag.
Basically, it makes the car more responsive, but at sacrifice of
noise, fuel economy, and potentially some engine life. Frankly,
especially given it is a 6-speed, I would have much preferred if
Mazda made 6th much taller.

Another reason why a manual might be geared shorter than an
automatic is for perceived drivability. Imagine if it turned
2000rpm at 60. You press on the pedal ... nothing. You have to
downshift. And automatic would do that for you, uh, automatically.
Thus perceived better drivability.

And, as Lanny also said, 6-speeds are in vogue. A Corvette, or any
similar torque-monster, simply doesn't need them. Lexus is coming
out with an 8-speed automatic. Why? Because MB has seven!

Oy.


Anyway, enjoy the car. If the noise gets to be a hassle on a
highway cruise, do what a lot of us do: earplugs.