|
 At the end of my
previous story I described the
upcoming update for the car to be performed on the fall of 2006: Suspension
system replacement. It was done on schedule and it included re-valved Konis,
stiffer springs, thicker anti-roll bars and adjustable front/aft camber
plates.
Roundel, BMW Car Club
Association’s magazine, reviewed the DINAN M Roadster prototype when it was
first manufactured (dubbed ISR3 for Inter-cooled Supercharged Roadster); and
concluded that the suspension and chassis modifications (which my car has),
placed the car in a totally different league from that of the stock car. In
a bid to experience for myself said difference, I decided to test the car in
a twitchy road, before and after the suspension upgrade. I chose CA-152
between Gilroy and Watsonville, California. It is a 2-lane road which, on its mountain segment, has a speed
limit of 40 mph. Most of the curves have a suggested speed of 25 mph, a few
are marked 20 and one is so closed that it is marked at 15 mph. Although I
had driven in twisty roads before, I had never tried to test the car’s
limits and therefore I did not push it to the point for the tires to chirp.
The best I could manage to do at the 15 mph curve was 30; and I felt the
car’s body roll. I was able to keep the car at the road’s top limit of 40
mph on the other curves and tried to imprint in my memory the firmness (or
lack thereof) of the car going into and out of the curves in order to
compare them with the handling of the soon to be modified car. A few weeks
after the upgrade, I took the car on the same course for another run. Even
though I was determined to evaluate all the curves, I knew that the litmus
test for the upgrade would be the 15 mph curve. Without tire chirp, I was
able to get 35 mph; and the car felt more secure with less amount of roll.
This time I had to carefully watch the instruments in order to keep the car
within the road’s speed limit as I found myself exiting from some curves at
45 mph.
The new limiting factor is the
rubber’s footprint. At the time of this writing, the first set of tires due
for replacement, are the rear ones. Without changing the stock wheels, I can
increase tire width by 10 mm front and aft. Since the car is also my daily
driver, I won’t put R compound tires as I already spend a lot on them as
they are. Overall, the suspension upgrade was exactly as described by
Roundel and other magazines that tested the DINAN-modified car: Exhilarating
fun on dry windy roads.
While the stock
car was never a slouch, one can always welcome a few more ponies under the
hood. At the beginning of 2007, DINAN fitted my roadster with their
supercharger system; designed to greatly increase the performance envelope
of the car while keeping the original around-town drivability. The upgrade
included a higher capacity radiator fan and fan clutch, and I added a bigger
throttle body. The end result is an increase of 100 hp and 70 lb/ft of
torque; although, with my engine, being as old as it is, I see lesser
increases. Nevertheless, the jump in performance was instantly noticeable.
Equally noticeable was the stock-like drivability: On my way home the day I
picked the car from the DINAN shop at Mountain View, CA, I was impressed
with the docility of the car on the streets. Aside from a minor increase in
pressure on my back while accelerating the car from 1st to 2nd
gear and the unavoidable noise, I would not have noticed the existence of
the blower.
I have not been able to perform
comprehensive tests yet, but I already have experienced substantially faster
launches and, provided I keep the engine at a minimum speed of 3500-4000
rpm, I always have acceleration power on reserve, even on 5th
gear. The icing on the cake comes when I go to the gas pump: The lofty
performance comes with only a 2 mpg penalty. I have not yet ran down a full
gas tank while demanding the most from the supercharger as I have done
several times with the unmodified engine; but I have routinely confirmed
that with the cruise control engaged at 65 mph, the supercharged car makes
23 mpg. I never got above 25 mpg before on the same speed conditions with
the stock engine. When in “racing” mode, the stock engine gave me 22 mpg.
For comparison, a new M Roadster, with a 3.2 litter, I6 engine tuned to
output 330 hp has been rated by the EPA to yield 24 mpg on highway. My
supercharged roadster makes 23 mpg. Many V8 powered cars with comparable
performance have more taxing fuel consumption.
To me, the supercharger is all
about acceleration, rather than top speed. What I love the most is the
improved ability to increase distance from cars following me. I almost dig
to find an impertinent driver pressing me to go faster. I would quietly
shift down one or two gears and, pressing the pedal to the metal, watch the
person’s car getting smaller by the second. More often than not, after a
couple of minutes I would revert to cruising speed and move one lane to the
right; waiting for the poor devil to catch up with me and letting him/her
get ahead. By that time they know that I am letting them go because I want
to, just because I can… I know, I know, I am showing off. But, hey, I love
it!
Could it get any better? Aside
from wider wheels and tires, I still have more upgrades in store: A
limited-slip differential which would multiply torque at the wheels by about
8% with only a minor top speed penalty (I don’t drive my car at the
drag-limited top speed anyways). This upgrade will also increase the ability
of the car to accelerate during turns. An oil cooler would be a welcome
addition for those summer months; and finally, a larger diameter air flow
meter will be a nice and cheap complement to the increased throttle body.
The DINAN ISR3 featured an
air-to-air intercooler and a larger diameter intake manifold valve which
resulted in another 50 hp and some extra torque. However, they don’t do
those anymore and probably the performance increase vs. its cost is not
justifiable. Besides, I also need to consider that, in order to keep the car
as a daily driver for the next 5 years (at least), I will have to put a
brand new engine; and those M machines are not cheap.
Because of the way I have
structured my business, it is more advantageous for me to maintain my
current car (however expensive it might seem) than to purchase a new
vehicle. With all the enhancements I already have and the few I still want
to add,
I can afford to be patient and aim for the big guns: A Porsche 911 GT3 or
the ultimate Porsche: The 911 Turbo! But let’s not get ahead of ourselves; I
still have plenty of experiences to enjoy in my now Supercharged M Roadster.
This was just Part 1… |
