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<blockquote data-quote="timetraveller" data-source="post: 6448" data-attributes="member: 456"><p>Nice to see a little reality creeping into this discussion on BHP. Our newby is likely to be seriously disapointed if he believes some of the earler figures. For example, Roy Roberston's Egli produces almost exactly 100 BHP at the rear wheel but that is a 1275 cc engine with bore up to 90mm and stroke increased. You would not want to ride Roy's bike in traffic. Increasing the stroke is interesting in that the ratio of the length of a Vincent con rod to its stroke is so extreme that it is not even on the table of what is recommended in modern tuning books. See Tom Gaynor's comments for a good book to start with. When the stroke is increased a shorter con rod can be used to keep the cylinder height the same and this in turn makes the con rod to stroke ratio better. There is one well known club member, who I will not name as he might not want his details publicised, who has progressivley shortened the length of his con rods over the years and they are now half to three quarters of an inch shorter than originals. His 500 engine regularly outperforms all other similar sized engines in the type of competitions he enters. If torque is required then shorter con rods are the answer. In discussions with a professional car engine tuner several years ago about this matter he seemed surprised that this was even a topic of discussion. It seems that in the car racing world there is sufficient money to have engines built with different length conrods and the engines are matched to the requirements of the cicuit to be raced on. So far as I know the only Vincent to be producing 100 BHP from 1,000 ccs on petrol, as opposed to dope, is that of Steve Hammel whos cylinder head modifications were mentioned in this forum some months ago. He has done a seriously large amount of work to obtain that figure and should be heartily congratulated. Most of us are not gong to get that kind of figure out of our bikes.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 6448, member: 456"] Nice to see a little reality creeping into this discussion on BHP. Our newby is likely to be seriously disapointed if he believes some of the earler figures. For example, Roy Roberston's Egli produces almost exactly 100 BHP at the rear wheel but that is a 1275 cc engine with bore up to 90mm and stroke increased. You would not want to ride Roy's bike in traffic. Increasing the stroke is interesting in that the ratio of the length of a Vincent con rod to its stroke is so extreme that it is not even on the table of what is recommended in modern tuning books. See Tom Gaynor's comments for a good book to start with. When the stroke is increased a shorter con rod can be used to keep the cylinder height the same and this in turn makes the con rod to stroke ratio better. There is one well known club member, who I will not name as he might not want his details publicised, who has progressivley shortened the length of his con rods over the years and they are now half to three quarters of an inch shorter than originals. His 500 engine regularly outperforms all other similar sized engines in the type of competitions he enters. If torque is required then shorter con rods are the answer. In discussions with a professional car engine tuner several years ago about this matter he seemed surprised that this was even a topic of discussion. It seems that in the car racing world there is sufficient money to have engines built with different length conrods and the engines are matched to the requirements of the cicuit to be raced on. So far as I know the only Vincent to be producing 100 BHP from 1,000 ccs on petrol, as opposed to dope, is that of Steve Hammel whos cylinder head modifications were mentioned in this forum some months ago. He has done a seriously large amount of work to obtain that figure and should be heartily congratulated. Most of us are not gong to get that kind of figure out of our bikes. [/QUOTE]
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