In Search of the 11 Second CBX - page 3

Some hand-built 469A units arrived in the United States in early November 1979. We went back to the drag strip with CBX one-four-seven-one on November 7, 1979. The motorcycle charged through the quarter-mile in 11.859 seconds at 115.53 mph. The speed was up more than four miles per hour from the bike's previous best, a huge increase. We knew the motorcycle would make a lot more horsepower on the dyno than it had before.

It did. Maximum horsepower was up to 82.83 at 9000 rpm and 9500 rpm. At peak horsepower there was a pick-up of 11.24 horsepower. And above 5000 rpm, the gains were really impressive. At 7000 rpm the difference amounted to more than 7.5 horsepower. All of that thanks to the substitution of the 469A advancer for the 1980 CBX's original 469 unit.

This disassembled advancer shows two independent flyweights pivoting off single post below 422 code.		The 469 advancer has one flyweight pivoting on each post; 422 has one weight on one post; two on the other.

Or was it? Eleven horsepower by changing only the ignition advance curve? Since the motorcycle had been out of our possession for a brief period, we wanted to put 1471 back to its 71.59 horsepower specification (469 unit) and run it on the dyno. Someone could have fiddled with the engine in other areas to make ft stronger, right? Furthermore, we needed to know what the difference would be between the 469 and 469A advancers on the same day, run back to back.

Surprise! Instead of making 71.59 horsepower at 9000 rpm, the engine peaked at 77.21 horsepower at 8500 rpm. The dyno curves began to separate around 5000 rpm (about a two-horsepower spread) with the margin growing to about 5.5 to 6.5 horsepower at the 8500-to-9000 rpm levels. Where had this extra increment of power come from? We ruled out chicanery because we could verify that 1471's engine hadn't been apart. There was a possibility that the ignition timing might have been slightly retarded on the original 1980 CBX test, so we did a dyno run to determine how much horsepower would disappear when the ignition was retarded. Four-horsepower-plus went out at the peak. Still, we didn't think that accounted for the total difference. It was something much more basic. Heat.

The original dyno test of the 1980 CBX took place on an extremely hot day. In fact, the air temperature inside the dyno room was 116 degrees F. On the retest, more than a month later, the air temperature inside the dyno room was 86 degrees F. The difference in ambient temperature was 30 degrees F.

Handbuilt (from 422) 469A unit has solder on second, right-post weight; it gives full advance earlier than 422.		This is the production 469A advancer as supplied to dealers for retro-fit to replace single-stage 469.

The correction factor can compensate for day-to-day changes in air density and humidity to give consistent results, and temperature has a bearing on the correction factor because air density is a function of temperature and barometric pressure. But temperature can have a much more decisive effect than its relation to the correction factor. Some engines - like the CBX - are very heat sensitive. Remember, by Honda's own dyno data, a 25-degree hike in head temperature caused the peak horsepower to fall from 74.47 to 68.07. The CBX taxes the blower-cooling system at the Webco dyno anyway, and that's been a matter of record since Honda's engineers witnessed the first dyno of the CBX there back in 1977. Hot dry air - 116 degrees and very little humidity - would be just the thing to cause the CBX to get weak knees. The temperature difference alone 116 degrees F versus 86 F) was enough to explain how the same CBX engine could make 71.59 horsepower on one day, and 77.21 horsepower on another.

   

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