Initial thoughts were to put the I-Mark to use as a drag race car. It is the lightest
Isuzu chassis (offered in US Market), with the most potent Isuzu engine. However, the
non-independent rear suspension and complete lack of any stock suspension adjustment,
severely hinder the vehicle's potential for anything but straight line competition.
There are only two problems with that logical conclusion: First, import drag racing was
dead in the United States by the Summer of 2001. The national series had folded, and
outside local events in Los Angeles and New Jersey, there was no organized import drag
racing in North America. Second, Gateway International Raceway closed in 2010, and the next
closest quarter mile track would have been Kansas City or Chicago, some 250-325 miles
This left autocross as the only available option (Gateway was also the only area road
course, and road/club racing ceased in the area until the track reopened in 2010).
As pointed out, the I-Mark is disadvantaged by a beam axle rear suspension. The car was
designed, under General Motor's direction, to compete with the Volkswagen Golf/Rabbit. In
fact, the I-Mark (Chevrolet/Geo Spectrum) would be most accurately described as a Japanese
reinterpretation of the VW Golf/Rabbit. Sharing almost identical layout and detail, but
remade with more compact and more efficient components. In fact, GM and Isuzu beat VW at VW's
own game, by building a more reliable and higher performing copy of the Rabbit. Isuzu's
car had stronger engines and better build quality than VW. At the end of Isuzu's model run,
their performance version, the 1989 I-Mark RS DOHC 16 Valve, measured faster in 0-60 and quarter
mile acceleration, higher in cornering speed, shorter in stopping distance, and lower in
curb weight, than VW's larger displacement and higher power rated GTI.
The Rabbit was insanely popular in road racing and autocross, despite the disadvantages of
its suspension design. But the Rabbit benefited from a huge enthusiast and racing following,
who invested many millions of dollars modifying and upgrading the vehicle to overcome
its limitations. And the I-Mark had none of that following and received none of that racing
Autocrossing an I-Mark would be a daunting task. As described above, the I-Mark is not a
copy of the Golf/Rabbit, but a reinterpretation, built as an improvement on the original design,
from a Japanese perspective. Nothing is interchangeable. Most is similar, but not similar enough
for anything but learning by comparison. The more compact and efficient components would also
make adaptation of VW racing components impossible. Simple things like VW's standardized
replacement cartridges are 1/4 inch or larger in diameter to the Isuzu component. This meant
reinventing everything from scratch.
In addition, the condition in which the vehicle started would be the determining factor in
choosing a class to compete in.
Stock class was out of the question.
- The interior had rotted out and had to be discarded. Finding another interior proved impossible.
The interior was stripped.
- The engine and control system had been changed from original to the second generation pieces.
The engine model number might be the same, but any level of honesty brings the conclusion that
the car has an engine swap.
- The car had been converted to larger front rotors and four wheel disc brakes. More importantly,
the layout did not allow for a functional emergency brake.
- Racing wheels on hand from the DSP class Stylus were 15x7 with 205-50R15 R Compound tires.
- The opportunity to install a Tracmax Torque Biasing Limited Slip Differential had already presented
itself when the transmission needed service.
Street Prepared required an interior and a functional emergency brake.
That left Prepared and Modified classes.
D Modified presented an opportunity, as the St. Louis Region had two very talented, very experienced,
and very fast Lotus Seven drivers fighting it out each year for the Regional Class Championship.
D Modified also allowed for removal of body panels and more aggressive modifications, which
would allow freedom to play and develop designs that could be refined and tamed back to be made
into DSP legal. This provided the opportunity to use the I-Mark as a test bed for parts to
be developed for the DSP Stylus. The decision was made to enter the I-Mark in D Mod competition,
with a DSP legal engine, and aggressively develop the suspension and drivetrain.
The SCCA would later introduce the X Prepared class. The allowed modifications are below Modified,
but allowed some of the things outlawed in the B, C, D, E, and F Prepared classes, which were
desirable to the goal of using the I-Mark as a test bed for product development. In addition, X
Prepared is hte only class allowing non-US spec cars. As the owner of two non-US spec cars, this
would provide the opportunity to race those two cars if desired. X Prepared more closely aligned
with the goals for the I-Mark, and allowed the opportunity to race every car owned. Making it
the logical choice. Thereafter, the suspension and drivetrain would be modified to more closely
reflect the allowed modifications for X Prepared class.
From 2003 through 2006, it saw some use in D Modified class Autocross racing,
finishing first in D Modified points in 2003.
The solid beam rear axle of the I-Mark and more primitive suspension design makes it
somewhat poorly suited for autocross, and autocrossing a car built for drag racing is
somewhat a lesson in futility, but it is an exciting little car to drive on course,
easily lifting both inside tires on hard turns, scaring corner workers, and functioning
as a very good training vehicle, forcing drivers to drive smoothly.
In 2008, the suspension was redesigned, and the car placed into X Prepared
class autocross racing. Idiosyncratic handling issues were reduced, but driving
the car on track remained just short of terrifying. Without fully sorting out all the
handling issues, the car saw some impressive success, finishing first in X Prepared
Class Points in 2008 (second place was a $55,000 Lotus Elise Supercharged).
For 2009, the car returned to X Prepared class, facing not only the same Lotus Elise
Supercharged, but also a Factory Five Daytona Coupe. With a lot of suspension fine tuning,
the car once again edged out the Lotus and bested the Daytona Coupe by .460 seconds,
taking the 2009 X Prepared Class Points Championship.
For 2010, the I-Mark returned to battle the Factory Five Daytona Coupe and Lotus Elise
Supercharged, with additional competition from a Lotus Exige, Lancer Evo, Impreza STi,
and a race prepped Ford Taurus SHO. Without any suspension or engine changes, the
I-Mark was taken through a range of alignment adjustments, and by the end of the season,
was handling much more competently, though still with a touch of terror as the
transition from neutral to oversteer was a little too large of a step. The I-Mark once
again took first place in XP Class Points Championship.
The 2011 season began with another radical redesign of the rear suspension, after the
custom made springs were measured and found to be about one third the stiffness that had
been ordered. The corrected rear spring rate drastically improved the handling, and, after
re-sorting rear swaybar size, the transition from neutral to oversteer much more gradual
and controllable. Unfortunately, it took half the season to sort the suspension, and the
Daytona Coupe owner had been making equal leaps forward in suspension tuning as well as
driver skill. So, with the I-Mark handling more like the race car it was always intended
to be, attention was turned to driver training and increasing engine power. Time to train
the driver to shove the I-Mark up against it's new handling limit, and add some power
adders, like aluminum pulleys, header, and ignition system.
But the Daytona Coupe owner had built up a substantial lead by mid-season,
and with only five events left, there just weren't enough opportunities to beat the
Daytona Coupe owner. Two first place finishes and two additional finishes ahead of the
Daytona Coupe owner just weren't enough. The I-Mark took second place in the XP Class
Points Championship, between the Factory Five Daytona Coupe owner (first place) and
co-driver (third place).
2012 was a season of learning lessons the hard way. The season was started on 6 month
old Hoosier A6 tires. The tires seemed to be wearing extremely well with the well sorted
alignment and low vehicle weight. At mid season, the IPRT I-Mark had a strong lead in the
points competition. And at that same time, the tires reached the limit of their life, some
60+ runs, with half the rubber left. The gradual dropo ff in traction was very apparent in
increasing run times and frustration, but the tires did not become the obvious source until
Left-Foot-Braking became the standard driving strategy, based on Jinx Jordan's advice. And
brake rotor thermal capacity became a new limiting factor with the heavy brake use.
Just before the final double points event of the season, the original fuel pump died after 23
years of service. With the new pump installed, upper RPM power was significantly increased,
revealing a previously unnoticed high RPM fuel starvation problem. But increased power is not
a positive thing for a car on hard, gripless, past-their-prime tires, when the daytime high
temperature is 40°F.
Going into that final event, the IPRT I-Mark had an insurmountable, mathematical points lead.
Both the IPRT I-Mark and the Daytona had mechanical problems (tires for the I-Mark and engine
control system for the Daytona) which lead to a poor showing for both. But the Region decided
to change the points calculation method for this specific two day event, and the XP Class
Points Championship again went to the Daytona for 2012. The IPRT I-Mark taking second, and
the Daytona Co-Driver taking third.
2013 was a year of unseasonably cool weather. The IPRT I-Mark got a new set of Kumho V710
tires for the beginning of the season. The first three local events of the year had parka weather,
and the IPRT I-Mark experienced a serious snap oversteer, unable to run at speed without spinning,
and leaving three valuable victories squandered. Considerable attention was paid to refining and
correcting the rear tire pressure. The rear grip problem disappeared, and was believed to have
At mid season, the weather warmed, and the IPRT I-Mark stuck to the track like glue. The victories
started stacking up and the local competition from a JDM 1990 Honda CR-X SiR, a JDM 1999 Honda
Integra Type R, and a rear engine Factory Five GTM, could not keep up. The change to left foot
brake driving technique was really paying off. Driving the course was just a matter of pressing the
gas pedal against the floorboard and never letting off. Stomp the big Wilwood calipers to slow,
half brake pedal to drift a turn, point the nose through the field of cones, and hang on for dear
life. Corner workers asked how the car managed to run at full throttle through sweepers and turns
that every other car had to lift to go through. Spectators asked what kind of VTEC engine transplant
the Isuzu had.
Through the second half of the season, long time rival Factory Five Daytona Coupe made a strong
charge on the XP class points championship. The snap oversteer problem returned to the IPRT I-Mark
for the final three, cold weather events of the year. Going into the final event, the IPRT I-Mark
held a solid lead, but the car could not put in an on-power run without spinning, and the Daytona
took the championship without challenge.
The off season will be spent going over rear alignment settings and with a lot of attention devoted
to increasing the rear tire contact patch.
2014 was another unseasonably (abnormally) cool sunmmer with only one of the ten series events held
in 90+ degree weather. In fact, between the four cold Spring events and four cold Fall events, only two
events were actually warm enough to wear shorts. Tire traction was poor all season long.
At the beginning of the season, the IPRT I-Mark underwent significant alignment changes, de-cambering
and de-toeing the rear suspension, chasing the rear snap oversteer gremlin. This was followed by reducing
the rear spring rate by 11%, and the front alignment was de-toed. Factory Five Daytona owner and XP class
competitor, Mike Marshall, borrowed the IPRT I-Mark at the beginning of the year when his car was not ready.
After beating the owner in his own car, Mike commented that the car understeered nice and predictably, until
the driver touches the brake pedal, and then immediately spun. Attention instantly focused on the brakes,
revealing that the bias was severely to the rear brakes. The rear axle weight was too low for the rear
caliper size, and front rotor undersized. Without a smaller rear caliper available, the front rotor was
upgraded, and the bias was brought barely within the range of adjustment of the brake bias valve. At mid
season, the I-Mark no longer swapped ends when braking while turning, and the rear spring and front toe were
returned to their previous settings.
At the two warm and dry events of the season, good traction netted a 1.81 instantaneous G measurement, and
revealed that less than three gallons in the fuel tank would result in fuel starvation as the gasoline
moves to the ends of the tank due to the high cornering force. An in tank swirl pot is in the works.
The cold weather and rain at the end of the season made racing much like a dog with long nails running on a
newly waxed tile floor. The hot-dry weather optimum toe out and camber on the front, and R-Compound tires
made for a slippery mess. It became apparent that a new setup strategy is needed, as our climate cools and
we get fewer days with good tire grip. Cold and wet events at the beginning and end of the season will
require reduced toe and camber, and a cool weather treaded racing tire.
Off season work will involve replacing the front calipers with larger piston models to better match the
rear braking power and chassis weight distribution, as well as further work on roll center correction
to increase traction and acceleration at corner exit.
2015 provided some opportunities to test theories based on past years' experiences.
The Hoosier and Kumho R Compound tires never seem to get up to operating temperature or wear down before
aging and heat cycling out. A combination of the light weight IPRT I-Mark and the 205 minimum available
tread width. The Street Tire classes had a rule change from 140 tread wear to 200 tread wear, and a set of
unused 195-60-15 (Miata size) Toyo R1R tires became available for a good deal. (The Region Index
Champion traded up from his STS Miata and bought
Dave Montgomery's two time STS class
national trophy winning Honda CR-X. The R1Rs went on the heavier Kosei R1 wheels and paid for themselves
at the first three events of the season, all of which were cool weather and one was rainy. As event day
temperatures got above 80 degrees, the R1Rs revealed that they would get greasy with summer temperatures.
Four wheel drifting the IPRT I-Mark was fun and the car easily controllable, but did not yield good run times.
A bit of careful observation revealed that event site contour is more important than pavement condition.
Our lot at Family Arena is between a quarry and a river bank, and is always covered in grit. But that lot
has a smoother contour with fewer bumps and washboard dips than Gateway. Lesson learned, damper compression
cranked up for Family and turned fully down for Gateway.
Revisiting the three year old V710 Kumhos for a couple events, revealed that they had heat cycled and hardened
so that they would not stick to the pavement on days with below 90 degree weather. Grip would feel
strong right up to the point that the tail shot sideways and the IPRT I-Mark spun.
The Factory Five Daytona Coupe broke its driveshaft on its second outing of the season. Mike Marshall
continues to overhaul the car every winter getting closer to putting all that LS engine power down, and
shredded the U Joints in spectacular fashion crossing the finish line of a blisteringly fast run. This put
Mike out of competition for most of the year and took him out of the hunt for the Region XP Class
Other old friendly rivals would visit. The IPRT I-Mark edged by Jacob Burke's 160 HP RHD 1990 Honda CR-X SiR.
And it also edged past Agan Alkan's LS1 powered 1986 Mazda RX-7 (which arrived on a fully equipped NASCAR
style race trailer and had received a major suspension and handling overhaul since its previous visit).
Even on greasy R1Rs and heat cycled out V710s, the IPRT I-Mark was managing to maintain a position
mid-pack in the region's raw time event results. Faring a little above midpoint on handling courses, and
a little below middle on horsepower courses.
The IPRT I-Mark took the St. Louis Region 2015 Class Championship.
Over the course of the season, it was discovered that the car had a target painted on it's back, as several
racers in other classes revealed that they had been using the I-Mark's results as their benchmark for
comparison, and had been chasing it for several seasons. A Trans-Am owner and a Miata owner would frequently
comment about how successful they had been in catching the I-Mark. Jim Lynch's 230 HP EP Class 2002 Ford Focus
SVT Turbo chased for the first half of the season, then got a dyno tune mid summer, and became the chased
for the last half of the season.
Next year will see a new set of Kumho V710s for warmer weather, the R1Rs for cold weather, and another
summer of tuning.
How Fast Is It?
For comparison of different cars at different events, we use a statistic we have named the "Percent of Fastest Car".
It is calculated as follows:
[(Fastest Car's Raw Time / Competitor's Fastest Raw Time) x 100].
Through the end of the 2014 season, on R Compound tires, the warm weather event results for the IPRT I-Mark been
absolutely astounding. The car runs in the 90-93 raw time "percent of fastest car". Surprisingly, the
switch to Extreme Summer Performance tires in 2015 netted the same 90-93 raw time "percent of fastest car"
peak results, but improved consistency through the season, improving results in cooler weather and on wet
Note: Fastest "Car" means vehicles that are derived from road cars and could conceivably be licensed and driven
on the street under the most lenient inspection requirements. We exclude anything that is a Cart, Formula Race
Car, single seat open wheel car, or tube frame silhouette cars.
This statistic assumes that all competitors at a given event drove on with the same track conditions (rain, wet
pavement, temperature, etc.), and that there is an equal level of driving talent and fast machinery among the
top finishers at all events. Admittedly, championship tour events, events drawing 150+ competitors or a large
number of trailered, purpose built race cars, would probably skew less favorable results for comparison, while
events with fewer competitors and few, if any, thoroughly modified cars, would skew artificially generous results
for comparison. But short of running the cars at the same event on the same race course, statistics are
the only possible comparison available.
This is in a region that has two Evo School instructors competing, a half dozen regular participants in the
national championship, and some seriously fast machinery, including a growing number of purpose built cars
trailered to and from events, and former national championship winning cars.
Add to this the local track condition of broken, grit covered black top asphalt, which negates much of the
advantage of R compound tires, and this is even more amazing.
Looking around at the other Isuzu made and Isuzu powered cars actively competing in SCCA Solo, the
IPRT I-Mark is 3-7 seconds faster than any of them.
Dave Jackson driving a 1981 Isuzu I-Mark (PF RWD) in FSP class in the Crows Landing Pro Solo National Tour is
running in the 89/85* "percent of fastest car". (* - 85 if T2 Class [Time Attack Vehicle Class] is included).
Christian Borchert driving a Lotus Elan M100 Turbo in SSP class in the Saginaw Valley Region is running
in the 87 "percent of fastest car".
Eddy Borchert co-driving the same Lotus Elan M100 Turbo in SSP class in the Saginaw Valley Region is
running in the 86 "percent of fastest car".
Adam Barrera driving an Impulse RS AWD Turbo in XP class in the Detroit Region is running in the 86
"percent of fastest car".
William Beeble driving an Impulse RS AWD Turbo in SMS class in the Ohio Valley Region was running in
the 85 "percent of fastest car".
Keith Hagen driving an Impulse RS AWD Turbo in IMS class in the Snake River Region is running in the 82
"percent of fastest car".
Steve Lockett driving an Impulse RS AWD Turbo in STX class in the Philadelphia Region was running in the 81
"percent of fastest car".
Stefan Tomalik driving an Impulse XS in HS class in the Cal Club Region was running in the 80
"percent of fastest car". (Based on the video,
the car appears to have an aftermarket steering wheel more than 1 inch smaller than OEM [330mm vs. 380mm],
the airbag deleted, and aftermarket seats, which would bump the car to Street Prepared class.).
Nicholas F. driving a D Street Prepared I-Mark RS Turbo improperly entered in H Stock class in the Southern
Alberta Solosport Club (SASC) / Calgary Sports Car Club (CSSC) was running in the 78 "percent of fastest car".
As pointed out, this D Street Prepared prepped vehicle, with owner claimed: 20% stiffer custom springs,
aftermarket racing bucket seats, aftermarket racing steering wheel, power steering delete (available only on
1.5 liter carbureted model), air conditioning delete (available only on 1.5 liter carbureted model) and 200
pound weight reduction, was entered in H Stock class. The owner claimed to be an experienced autocross
competitor, but entered in the Novice class designation. Apparently, the miserable finish time of the vehicle
did not generate enough reason for the other competitors or the club to protest the entry and correct it to
DSP. That is because this driver finished 49th out of 51 cars that completed the course successfully. That's
slower than at least three entries by apparent girlfriends co-driving their boyfriend's cars, making a slow
parade lap, just to participate in their boyfriend's activity. 49th in a field of 51 would be the bottom 4%.
The SASC/CSSC actually use the "percent of fastest car" calculation we are using here, as indicated in the section
titled "Overall Ranking by Raw Time", and Nicholas F. earned a 78.353. It's no surprise that Nicholas F. put the
I-Mark RS Turbo up for sale immediately following the event and unloaded the car as quickly as possible.
These comments may seem a bit harsh, but Nicholas F. claimed this performance, finishing 11 seconds slower
than the fastest car at the event, qualified him as a champion. Anything above the 85th "percent of fastest car"
in an event with 100+ participants is pretty respectable. But a 78th "percent of fastest car" in a small event
like this, really indicates a broken car or that the driver got lost on course or spun a couple 360's while driving
The "percent of fastest car" can be used to predict the raw time for a car and the driver of that car. Take
the FTD for the fastest car (excluding karts), divide by ("percent of fastest car" x .01). The result is the
expected raw time for the car and driver at that event. The difference between the 93 "percent of fastest car"
and the 87 "percent of fastest car" on a 50 second course is 3 seconds. The gap grows larger for all the lower
"percent of fastest car" numbers.
Consider that the Elan M100 is recognized as the best handling FWD car ever
made, the 90-93 Isuzu cars benefit from independent rear suspension and redesigned front suspension, that the
85-89 I-Mark with twist beam non-independent rear suspension is arguably the worst handling car that Isuzu ever
made, and the 30+ HP advantage that all of these turbocharged cars have, and the run times that the IPRT I-Mark
is turning are mind blowing.
To go back to the ISUPAGE Directory,