Read an excellent article on DSR
racing, with specifics about Lutrell Harms' car. The article was written by Paul Haney of
Inside
Racing Technology.
Excerpts are copied below.
Lutrell Harms built, drives, and maintains his car,
the blue number 74, for a minimum of cash. On race weekends Lutrell's
wife, Terry, becomes his pit crew. Among West Coast racers Lutrell is
credited with reviving the class by showing that a simple, fast, fun
racecar can be built for around $10,000.
Chassis
Lutrell Harms used the familiar Crossle 32 FF
chassis as a starting point for his DSR. He spent 2 years of his spare
time and about $10,000 building his DSR, patterning the body shape after
the Swift DB-2 Sports 2000 and adding a rear wing. Lutrell used square
alloy-steel tubing for the main chassis rails and round mild-steel tubing
for stiffeners. The front suspension utilizes unequal-length A-arms
ball-jointed on all ends. The rack-and-pinion steering rack mounts behind
the front axle line. The tubular front and rear anti-roll bars were
fabricated, as were most of the mechanical components, by Lutrell.
Anti-roll bar adjustment uses sliding clamps to increase or decrease the
lever arm.
The brakes are AP two-piston calipers using 10-inch
solid rotors and driver-adjustable bias. "I'm not down to minimum
weight," Lutrell said. "So I'd rather not use the heavier vented
rotors. The cars keep going faster though and the brakes are getting
marginal. ... The glass fiber body work is heavy and it would be very
expensive to duplicate in carbon fiber."
Lutrell's car uses 13-inch diameter wheels front and
rear and bias-ply Hoosier racing tires measuring 7 inches wide front and
10 inches wide at the rear. The dampers, mounted inside the usual helical
coil-springs, are Penske double-adjustable units. "I don't adjust
them much," Lutrell explained. "It feels OK, and I don't test
enough to come up with new settings."
Engine
The engine is a 1,000 cc four-cylinder, DHOC,
20-valve unit from a Yamaha FZR 1000 motorcycle. Lutrell says it produces
about 155 hp at 11,500 rpm and 83 ft-lbs. of torque at 10,000. Fuel and
air are metered by four Kehin slide-valve carburetors. "The stock
Mikuni carbs don't work," Lutrell said. "The float bowl allows
the fuel to slosh around too much. I've got the same problem with the oil
pan. A motorcycle leans in a corner so they don't need a baffled pan. I
should have a dry-sump system and an oil cooler, but I get away with
putting an extra quart of oil into the engine."
The crankshaft is stock as are the valves and valve
springs. High-compression pistons, custom piston rods, and special
camshafts are the major engine modifications. "I use the stock
ignition system," Lutrell said. "These engines have been
available in wrecking yards for as little as $800 but lately they cost
almost $3,000."
Cockpit
The cockpit instrumentation is straightforward. An
electronic system commonly used on karts shows rpm and mph on an LED
display. The unit retains maximum readings and stores the data from 1 lap.
Round, analog gauges are used for oil pressure, oil temperature, and water
temperature. A separate unit to the right of the steering wheel records
and displays lap time with the aid of a track-side beacon.
Lutrell uses the stock Yamaha 5-speed gearbox with
chain drive to a locked rear axle with constant-velocity joints and half
shafts. He has also fabricated a unique mechanical gearshift system
utilizing up-shift and down-shift paddles behind the steering wheel
connected to the stock shift links with steel cables. "I added a
neutral light and gear indicator lights to the dash. Braking into a corner,
the down-shifts can happen very fast."
The rear suspension locates the drive wheels with trailing arms, an upper
lateral link, and a reversed lower A-arm. Springs and dampers are
identical to the front suspension except for spring rate and damper
settings.
Aerodynamics
The car's aerodynamics is a product of the continual thought and constant
experimentation of the designer/engineer/driver. "The front winglets
cured a high-speed push," Lutrell explained. "I have another
nose that has a diffuser built in but it created too much downforce. The
car bottomed and I didn't have time to find the right front springs. The
way the car is right now I can feel the rear wing vibrating at speed and I
think the air is blowing up off the nose creating turbulence. I'm going to
add a small dam on the top of the nose to spoil the air and decrease the
separation."
After a project of this sophistication has been in
use for a time improvements come to mind. Two years ago, Lutrell added
some chassis tubes to stiffen the car. He knows what he would like to do
to make it faster, "I have a lot of ideas but I'd have to build a new
car."
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