Amici,
Some of you guys are smart beyond belief. How the dickens you know so much?
It's got to be luck. In any event, I'm not only impressed, but I might even
start to pay a little more attention to some of the stuff that transpires
across this neck of the web.
Now to the subject at hand. First, the disclaimer. I don't know about other
dynos, but the one we used is analogue and very dependent on judgements in
reading vibrating dials, albeit very large ones. The operator has to
adjust the torque control whilst simultaneously adjusting RPMs. The
"reader" must catch the proper moment of stabilization to write down the
readings.
Our MO was to set up readings at 500 RPM increments starting @ 3000 up to
5500 RPMs. The ambient temperature when we started was 82d F and the
humidity 75%. We're at 1000 msl.
Before we put on the 2" SU carbs, we made a trial run with the old 1.75"
Strombergs with no stacks. At 5000 RPMs we recorded 105 hp.
The first serious run we made was with the timing set at 30d btdc. The SUs
have the short velocity stacks. Their usefulness became abundantly clear
when the engine was run at speed with a load on it. Looking into the
carburetor there is an incredibly full, dense, swirling mass of fuel being
sucked violently into the engine. It was an awesome sight to see the power
of aerodynamics of the ingestion system of a carburetor.
The results were as follows:
5500 123.3 ft lb 123.3 hp
5000 129.2 123.0
4500 130.3 111.7
4000 130.9 99.7
We then removed the muffler and made one run @ 5500
5500 115.9 121.5 hp
We then set the timing @ 33 degrees with the following results: (w/muff)
5500 114.5 120.1 hp
5000 131.5 125.2
4500 132.1 113.2
4000 133.2 100.6
3500 133.2 88.8
3000 128.6 73.5
The EGT was 1400 degrees and with our richest needle (Uhs) the engine was
still running too lean. Bob filed the needles a pretty good bit but it
only brought the EGT down to 1325. I've ordered a set of UAs, UFs and Ugs
which we believe will help the top end some. By the time we made our last
run the OAT had risen into the low 90's but I didn't make a new correction
factor. With the new needles and a new CF maybe I can find 130 hp. But
maybe not. In any event, I feel comfortable with a real 125hp @ 5000RPMs.
For my drive-to-the-race style, this suites me fine. The idle @ 1000RPMs
has a gentle lope but really not too bad. It was secured to rigid mounts
and it might be a little worse in the flexmoblile. But I will still be able
to take the kids to the super-cooled Piggly Wiggly to escape the hot summer
Georgia nights.
Share your thoughts about my readings.
Richard Taylor
Atlanta
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