Kenny Dreer 880 pistons

Steve Oszko was the top A grade racer in Victoria when Manx Nortons were the go. His 500 Manx was the most developed. But his 350 Manx was more interesting. It was ex-works, and he had bought it from Jack Ahearn. I did not see inside it, however apparently the cylinder head had two squish bands - one in the normal position, but there was another higher up which had been welded to remove it.

I was interested in the article about Joe Craig which was referenced in another post. It mentioned that Joe ran the Manx Nortons very lean and had help from a chemist who was involved with combustion processes. During my working life, I was involved with closed vessel testing of gun propellant. What it is, is effectively the breech of a large gun fitted with a pressure transducer to measure the pressure changes. Normally what you get is a pressure rise which peaks in a desired time after detonation. Which gives you a rate. But with gun propellant there is a concept known as 'brisance ' - it is the rate divided by the time - in effect a measure of the acceleration of the flame front. It is a similar concept to Octane Rating. I use methanol fuel which has unlimited knock resistance. However methanol has about 0.8 times the calorific value of petrol and the jets flow twice as much depending on the compression ratio. I have come to doubt the benefits of running high compression, unless the compression can be raised without destroying the shape within the combustion chamber.