[DeTomaso] Steel vs aluminum flywheel

[Daniel C Jones]

> when I ran a Dynomation simulation, my motor would have twice the torque
> at 1,000 RPM of a normally aspirated engine with a big cam and carb due
> to the cam the turbos like, so I think either flywheel will work well on
> the street.

Dynomation is quite optimistic at low RPM (below peak torque).  Also,
the value it returns assumes WOT and tuning is largely irrelevant at
part throttle, so the difference in WOT torque is not important.  More
important will be the mild cam timing associated with the turbo engine.
Assuming your first gear remains a 2.23:1 and you are moving from a
4.22:1 to 3.2:1 final drive ratio, a vehicle weighing 3200 lbs will
now appear as if it weighs 4220 lbs when starting from a stop.  I've
calculated and posted the numbers for the effect of reducing flywheel
inertia before.  The effect is quite large in lower gears where you will
be traction limited and negligible in higher gears so I'd go for the steel
flywheel.

The T5 in my '87 Mustang GT has a 1st gear ratio of 3.35:1 and a 2nd gear
ratio of 1.93:1.  It also has a final drive ratio of 3.08:1 which means
the combined gear ratio in first is 10.318:1 and is 5.9444 in 2nd gear.
With a 2.23:1 first gear and 3.2:1 final drive ratio, you will have a
combined gear ratio of 7.136.  If my Mustang had the popular 3.55:1
final drive ratio, starting off in 2nd gear would be equivalent to
your Pantera starting off in 1st gear.  I wouldn't want that at all and
certainly not with a lighter flywheel.

I think you'd be happier with a 3.56:1 or 3.77:1 final drive ratio combined
with a shorter 2.86:1 second gear and taller 0.62:1 5th gear.  I think Kirk
may have a 3.56:1 ring and pinion on hand.  When we discovered the corrosion
problems in my red Pantera's ZF, I wrote a program to help me evaluate
various gear ratio combinations.  It figures out the RPM the engine falls
back to at each shift, assuming instantaneous shifts and no tire growth.
Results for a few combinations I ran are below:

Dash 2 ZF with 4.22:1 final drive ratio, 0.705:1 5th gear, 335/35/17 tires
Shifting at 6500 RPM
Shifting from 1st to 2nd, Fall Back Engine RPM = 4284.8 at  53.9 MPH
Shifting from 2nd to 3rd, Fall Back Engine RPM = 4598.6 at  81.8 MPH
Shifting from 3rd to 4th, Fall Back Engine RPM = 5287.5 at 115.6 MPH
Shifting from 4th to 5th, Fall Back Engine RPM = 5416.7 at 142.1 MPH
Cruise Speed of 80 MPH is 3050 RPM

Dash 2 ZF with 4.22:1 final drive ratio, 0.62:1 5th gear, 335/35/17 tires
Shifting at 6500 RPM
Shifting from 1st to 2nd, Fall Back Engine RPM = 4284.8 at  53.9 MPH
Shifting from 2nd to 3rd, Fall Back Engine RPM = 4598.6 at  81.8 MPH
Shifting from 3rd to 4th, Fall Back Engine RPM = 5287.5 at 115.6 MPH
Shifting from 4th to 5th, Fall Back Engine RPM = 4763.6 at 142.1 MPH
Cruise Speed of 80 MPH is 2682 RPM

Dash 2 ZF with 3.56:1 FDR, 2.86:1 1st gear, 1.72:1 2nd gear and 335/35/17 tires
Shifting at 6500 RPM
Shifting from 1st to 2nd, Fall Back Engine RPM = 3909.1 at  49.8 MPH
Shifting from 2nd to 3rd, Fall Back Engine RPM = 3930.2 at  82.8 MPH
Shifting from 3rd to 4th, Fall Back Engine RPM = 5287.5 at 137.0 MPH
Shifting from 4th to 5th, Fall Back Engine RPM = 5416.7 at 168.4 MPH
Cruise Speed of 80 MPH is 2573 RPM

In addition to 0.62:1, I believe there are 0.642:1 and 0.655:1 5th
gears available to replace the ZF 0.705:1 5th gear.

Dan Jones