Introduction: Recently I had the pleasure of a long chat with Chuck
Salmen, builder, owner and co-driver of the $um Fun Roadster and
interviewed him about the technical detail of the car. He reviewed what
follows and authorized its online publication, which I'll divide in half
to keep it from being too long at one go.
This is presented for your enjoyment and use, AT YOUR OWN RISK. In
other words, if you try to use these ideas, and tear your car up, and
kill yourself, don't run to me, or Chuck. Race cars are SERIOUS fun.
Chuck does like to hear from people with Bonneville roadsters, who want
to chat about technical improvements. He feels that safety and
stability are extremely important in a speed trials car. You don't want
to hurt the driver, hurt the car, or lose the time, effort and money
invested.
Bill: Chuck, most Speed Trials people are familiar with the beautiful
$um Fun '34 Ford HiBoy Roadster that holds the Bonneville AA/GR record
at 250.545 (new record Oct. 22, 1999 252.908). Your car is noted for
its high speed stability and reliability and I wanted to ask you about
the technical detail that makes this happen. I am indebted to Wes
Potter for putting me in touch with you.
Chuck: Sure, Bill. The car has been featured in magazines before but
no-one has written anything about the technical side of it.
B: What is your background at Bonneville?
C: I went there first in '57, and from time to time after that. I
raced motorcycles and we ran a motorcycle streamliner years ago. I
built this car in '92.
B. Why the '34 Ford HiBoy?
C: I always liked the looks of the '34 Ford body. I believe it cuts
the wind a little better than some others, and has a natural down-force
about it. You see we have kept it stock frame rails and body, even
though the front is reproduced in one piece for ease of maintenance. I
didn't want to lengthen the hood, and though the driver is in the center
to keep the car symmetrical, we didn't put him all the way back.
B: I understand roadsters have always had a tendency to instability and
spins at very high speeds, yet yours seems to run on rails. What are
your secrets?
C: A lot of things are at play here. The total weight of the car, the
center of gravity, the weight distribution, location of ballast, wheel
spin, and torque effects on the rear axle. This car weighs around 4000
pounds. I built a heavy, super-strong roll cage for it, not only for my
own safety, but because my son co-drives. I use steel plates for
ballast, with about 75 pounds behind the front axle and 700/800 pounds
on the floor under the driver's seat. You don't want ballast behind the
rear axle, it gives a destabilizing pendulum effect if you have any
fishtailing. With a big engine you may have 1000 ft lbs or more of
torque coming down the driveshaft to the rear axle, depending on what
gear you're in. This tends to lift the left rear wheel and reduce total
traction. I use a locked axle, with coil-over spring suspension, and
adjustable linkage that allows me to 'jack' weight from the right wheel
to the left. This offsets the driveshaft torque effect so both wheels
feel the same weight and tend to drive the car straight. I believe this
setup is of great value on my car. (Bill's note: This is DEEP. Take a
look at Chuck's car and talk to him before you try to copy this rear
axle setup!)
The CG is as low as we can get it. The body, as noted before, seems to
have a natural downforce effect (3 degrees approach angle), which I have
actually measured with sensors that record suspension deflection at
speed. Another trick we do is use stabilizer bars on both axles to keep
the car flat. These work the same as those on current production cars.
One more detail I think is valuable is custom wheels to reduce run-out
of the tire/wheel assemblies to the absolute practical minimum. I use
MT 875/18 tires on the rear and since every tire is different, I adjust
the pressures a little to get them as close as possible to the same
measured circumference. You need the truest possible, carefully
balanced wheels to get the best possible traction. Otherwise your tire
is constantly jumping off the surface. Wheelspin is dangerous. I
believe roadsters have a critical speed around 225/230 mph and a lot of
them get into trouble there.
B: What is your axle design?
C: For a long time, I used a locked Champ car back axle, with a QC, but
due to recent signs of overstress, I went this year to a Winters that
uses a locked nodular iron 9" Ford third member. Our front axle is a
home made tubular using coil-over springs with adjustable-dampening
shocks.
B: So no more quick-change gears?
C: Our Jerico 4-speed gearbox has a feature that several under and
over-drive ratios can be fitted on 3rd gear. So top gear (direct)
becomes 3rd gear and the old 3rd becomes 4th gear. But it's a four hour
job to pull it all apart to change the gear ratio.
B: Tell us about the all-important power unit, I gather it is a BB-Chev
type.
C: You might say that but in fact the engine I've used for years is a
540 c.i. Donovan aluminum block and heads with not a single Chevy
production piece in it. This has been very good, but this year I've
stepped up to a 603 c.i. Merlin iron block to overcome some shortcomings
I feel the aluminum block has in an endurance situation. On the Long
Course full power (around 2 HP per cu. in.) is held a long time and I
saw evidence of the block flexing and the iron liners moving and
distorting a bit. I expect more rigidity in the iron block but I still
use the all-out racing aluminum heads which have huge air-flow
capability.
(Continued in Part Two)
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