Well, last Monday I got to run the Works Midget up on a chassis dyno and it
was quite an experience.
Having bought an hour of dyno time in a benefit silent auction, I decided it
was an opportunity to see what a little porting and a mild cam would do to a
stock 1275, as well as a chance to optimize my ignition timing. In the
company of several friends (Rick Fisk from the Spridgets group, fellow MG
Vintage Racers competitor, Dave Smith who runs a very nice MGA, and Bob
Lawrie, my ice-racing partner in the 3-wheeled Honda CRX effort) I went to
Jackson, Michigan and Paul's High Performance, a very sano Mustang tuning
and drag race shop (www.paulshp.com).
One hour gave me enough time for a warm-up, strapping the car to the
rollers, and six pulls on the dyno. With Paul himself in the car and a
remote control module in his hand, he watched the computer monitor which
showed him in one display a video speedometer and a tach. He ran the car
through the gears, and then did a pull to redline from 2500 RPM. The dyno's
computer samples several hundred times per second and calculates mean
horsepower and torque figures through the entire range. The operator can
pull this up on the screen and print it out, both numerically and in the
form of a graph (or "curve" if you've heard that term applied to HP and
torque). Two pulls are done for a baseline (what we call the control
condition in my business). Then you change an independent variable and do
another two pulls (the "research condition," if you will).
We noticed some black smoke in the exhaust prominently at a couple of places
during the "acceleration" of the car. Paul's expert eye on the spark plugs
under a microscope (over 250 cars dynoed last year), and the suggestion was
leaner jet needles. I had gone to Vizard's recommended AF needles after
porting, but had brought along my old needles, which are still a bit richer
than the stock 1275 carb set-up. In went the H6 needles (the dependent
variable) and another two pulls. No smoke, nice plugs, and some improvement
in power. What was noticeable however, was the curves were a lot smoother.
And the car sounded better.
In the remaining time I decided to retard the timing from the 33 degrees
full advance to 31 degrees BTDC. I don't want to hole a piston on the track
and I'd prefer to not have to run race gas at $5 a gallon when I might get
away with 93 PON off the street. Well, the HP was just about the same.
Torque was lower, but insignificantly. And the curves were even smoother.
Paul's verdict: Race with pump gas, run those cooler NGK BP8 plugs, and
keep the timing at 31.
Results: peace of mind on the track. All I have to worry about now is
throwing a rod or breaking a crankshaft!
Oh....and I discovered that my mild cam, porting, small-bore Maniflow
3-into-1 header, and 10.9:1 CR gave me just about 74 HP at the rear wheels
with the curve starting to flatten at 6500 RPM. Nothing to be gained by
pulling to 8 grand on this engine! Torque curve showed its sweet spot
between 3500 and about 5000 RPM. I also learned that my speedo was from
Mars and my tach reads 600 RPM too low.
All in all, a unique and interesting experience.
See ya at the Gold Cup Historics at VIR in June!
John Deikis
Chelsea, MI
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