Just picking this thread back up: as an old man and unlike a lot of the SOHC crowd I saw some of (but not all) the multicylinder flat track machines race - on the Syracuse Mile.
They didn't work.
A lot of the reasons why were stated before but not some of the important ones. One, the firing pulses of a V-twin make them much more friendly on a dirt track. This has been true since bikes were first raced on flat dirt tracks. Second, the Triples, TZ's, Hondas, Kawasaki Triples et al all had their power bands in the wrong place for a dirt track and it just isn't always possible to ride around that every time. Third, low weight makes a difference, and nobody can make an SOHC light enough to be viable against a V-twin Harley XR. When Honda went dirt tracking, what did they use, a V-4? Nope. A V-twin, more than once.
Even paralell twins (BSA, Triumph, Yamaha, Norton, Royal Enfield, Benelli..Benelli?) had a better time of it than across-the-frame multis.
The dirt track multis I saw raced all dug holes in the ground at the start and halfway down the straight and were late to the first corner. They might have had speed on the straightaways, but the lighter twins would kill 'em in the corners while the multis were either fighting their way around or trying to find the powerband. I mean, I have pictures of dirt track twins with their crankcases in the dirt they were leaned over so far - can't do that with a multi.
It was a dead end. Oddly enough, the British bike guys figured it out early and dropped the BSA/Triumph Triples from the dirt track roster, and they didn't get traded down to "local" tracks. They disappeared.
Keen bikes to look at now. Not winners in their day, and a technological dead end. Maybe with those oft-rumored magnesium CR crankcases? OK, nah.
Spirit
