Snappier Response
If you’re really getting into doing track days or
autocrossing, and haven’t considered replacing the clutch and flywheel with a
quick-reaction clutch and lightened flywheel as we discussed in the preceding
section of the book, now is the time to consider doing that upgrade. If you can
make your downshifts into corners quickly, losing as little time as possible
coasting between gear changes, your lap times will improve.
A performance clutch and lightened flywheel is key to this
aspect of your driving. For the same reason—improving your performance through
the gears—a close-ratio gear kit can help reduce your lap times.
Tilton High-performance Flywheel and Clutch
If you haven’t yet made the change, and are serious about
finding every tenth of second that you can, you may wish to consider doing what
the pros do and replacing your MINI clutch and flywheel with a Tilton
high-performance clutch and flywheel.
This substitution offers several advantages over stock
components and less-expensive upgrades. Going from front to back, the system
starts with a light, balanced flywheel weighing only 11 pounds, which means the
minimum amount of inertia and quicker response. Behind the flywheel is a
smaller-diameter lightweight clutch, which means less weight in the car and a
reduction in rotational inertia as with the flywheel.
The clutch disc itself has a cera-metallic surface, which
means quick pick-up with no clutch fade over a long race. Finally, manufactured
to racing standards by a well-respected racing supplier, this whole system is
guaranteed to stand up to racing demand and provide long-lasting performance.
The only drawback to the competition clutch is that it does
away with the vibration-damping springs with which the stock flywheel is
equipped. As a result, your Tilton-equipped MINI will be louder at idle than a
stock MINI. But then quiet idling isn't the point, is it?
As you might expect, the Tilton materials and manufacturing
quality are going to cost a little more than typical clutch and flywheel
upgrades, but the performance and especially the durability make it the best
choice when you’re seeking to be the very best. The full kit, including
flywheel, clutch disc, pressure plate, throwout bearing adapter and
installation hardware costs about $1500.
Straight-Cut Close-Ratio Gear Kit
When the engineers are selecting gear ratios for a manual
gear box, they’re generally going for the best gas mileage possible. That means
that gears are selected to produce reasonable torque at the lowest possible
engine speed, which may not be what you’re looking for in a track car. They’re
also assuming that the average driver may not be all that precise in shifting,
so they’ll use bevel-cut gears to reduce the possibility of grinding gears when
shifting.
In racing, you’ll sometimes hear drivers bragging about their
“close-ratio” gearbox. They’ll also talk about using “straight-cut” gears in
the gear box.
The first term—close-ratio gears—describes a gear set that
has different ratios than the standard gears that are installed in stock MINIs.
The purpose of installing a close-ratio gear set is to keep the engine well up
in the power band (which as you may remember really starts about 3500 RPM) at
the range of speeds common on a road track. It is especially important to
making sure that you have all the torque possible for those all-important part
of the turn where you are accelerating, because the car that accelerates faster
out of the corner will be the one that’s ahead at the end of the next
straightaway.
For comparison, the following table shows the ratios of the
standard five-speed gear box and those in an aftermarket gear kit available in
the aftermarket. To understand this table, remember that the lower the ratio,
the slower the engine is turning relative to the driveshaft at the
differential. So, for example, in first gear, the engine is turning 3.42 times
as fast as the shaft on the end of the transmission. You’ll note there’s little
difference between the gearing on the standard gearset and the close-ratio set,
since first gear is only used to get out of the pits.
However, the differences become more obvious as you move up
through the gears. There is a significant gap between first and second gears on
the stock gear box, going from 3.42:1 to 1.95:1. However, on the close-ratio
set, the ratio only changes to 2.333:1. From this, you can tell that the engine
speed will be much closer between first and second gear on the competition box
than on the stock box, which of course is why this is referred to as a
close-ratio box.
You can also see that the engine is going to be turning over
about 15 percent faster in second gear with the competition box than with the
standard box, so when the stock engine is turning at about 3000 RPM in second
gear, the engine in the close-ratio equipped MINI will be turning at about 3450
RPM at the same speed, or right at the point where torque really starts to
increase.
The difference is very marked in fifth gear. On the stock
box, the engine is actually turning slower than the final drive, the ratio that
is called “overdrive.” This overdrive ratio is excellent for highway driving
where you don’t need any real torque because you’re cruising at a constant
speed, but you want the best gas mileage. However, it would be totally
unsuitable for the track. In contrast, the close-ratio box has a gearing that
about 40 percent higher. So when the stock engine is loafing at 2500 RPM in
fifth—perfect for highway driving—the competition engine will be running at
3550 RPM to produce the same speed, right at the beginning of the power band.
With this gear box, the engine easily can be kept in the
power band at normal racing speeds in all types of corners. To stay equal in
acceleration out of corners, the stock MINI would have to be able to put
another 100 horsepower to the wheels.
Standard Close-Ratio
First 3.42:1 3.417:1
Second 1.95:1 2.333:1
Third 1.33:1 1.788:1
Fourth 1.05:1 1.429:1
Fifth 0.85:1 1.208:1
The second feature of this competition gear kit is the design
of the gears. In a standard box, the gear teeth are cut at an angle to the gear shaft so that two gear teeth are engaged at any one time. These are called
“helical gears.” By contrast, “straight-cut” gears have teeth edges that are
parallel to the gear shaft The helical gears significantly reduce the chance of
the driver grinding gears when shifting and they are also noticeably quieter in
operation than if the gear teeth were parallel to the shaft.
However, in racing the helical gear is slower to engage than
the straight-cut gear. Also, it doesn't transmit power as effectively as a
straight-cut gear. Since a race driver should be able to shift more precisely,
and gear noise is not an issue, for competition the straight-cut design is
preferred.
Most MINI owners who use their cars on the street as well as
for competition probably wouldn't enjoy the straight-cut gears in daily use.
They also require higher rev levels for given speeds because of their ratios,
so the competition box would deliver much lower mileage and greater engine
wear. However, for MINIs that are being built up primarily for track use, they
are worth serious consideration because of the competitive edge they provide.
The gear kit with the ratios described above is available for
about $3500. Since it requires removal of the gear box and replacement of the
gears, installation is best left to a service shop that is experienced in MINI
work.
Next Installment: More Stopping Power
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