The trouble is -- the market! Flat country = lower RPM needed. (Australia)
US- not so flat- higher RPM.
A stiffer 5th or 6th gear also causes a higher torque load, and higher
combustion chamber temperature.
(Not the favorate of warrenty sellers)
> wrote in message
...
> Agreed, 6th is a cruising gear. It shouldn't need high revs. If you need
> to be accelerating hard in overdrive, you need to rethink your driving
> habits and learn to downshift. That was one of my few major complaints
> about my '01.
>
> Eric Lucas
>
> "Chris D'Agnolo" > wrote in message
> ...
> > All good points but I agree with Dave, 6th should be a taller / more
> > relaxed cruising gear. I think the car has plenty of power / torque to
> > pull a somewhat taller top gear and it would be a big improvement in
> > highspeed cruising comfort and in real world highway gas mileage. Both
of
> > which the miata realistically falls down a bit on.
> >
> > Chris
> > 99BBB
> >
> > "M. Cantera" > wrote in message
> > ...
> >> The key de terming factor in the gearing of an engine is the torque
> >> the engine produces.
> >>
> >> Push rod V 8 engines are designed to produce high torque, partly
> >> because the push rod design limits the design to 2 valve per cylinder.
> >> This design, while economical, limits the rpm that the engine can
> >> turn. They usually red line at relatively low rpm (5000 to 6000 rpm)
> >>
> >> Modern fours, using overhead cams can uses three or four lighter
> >> valves with better modern spring, can turn 7000 or 8000 rmp. But
> >> since the are smaller displacement they produce much lower torque.
> >>
> >> The formula for horsepower is:
> >>
> >> Horsepower = torque * revs/minute * minute/60 seconds * 2*pi * 1/550
> >> Horsepower = torque * revs/minute * 1/5252
> >>
> >> In a very simple way:
> >>
> >> Suppose your car requires 100 hp to move along at 90 mph.
> >>
> >> A v-8 rated at 300 ft-lb at 2000 rpm will be producing 114. An
> >> engineer will pick the gearing and rear end to produce the right rpm
> >> at the wheels.
> >>
> >> A smaller 4 cylinder engine, producing 140 ft-lbs or torque would have
> >> to turn nearly 4300 rpm to produce the power necessary to move the
> >> same car at the same 90 mph.
> >>
> >> As for the gears, the turbo engine puts out 28 % more power than the
> >> normal engine, but the full turbo pressure does not kick in until 4500
> >> rpm. the red line is at 6500, so the maximum power band fairly
> >> narrow. If your gears are too wide, you can fall off the power band
> >> when you up shift, so having more gears allow you to keep the engine
> >> turning at high rpm while you accelerate. (its also more fun)
> >>
> >>
> >>
> >> On 20 Apr 2006 06:13:29 -0700, "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.
> >>
> >
> >
>
>