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I'm about to pull my 916 engined 748 off the road for a light overhaul post IoM trip. There isn't really that much I can do to make it much faster as the rider is the limit here. However I WOULD like to make it a bit quicker as I could handle that. The first priority will be later, lighter wheels. After that will be some engine tweeks. It's already as light as I can afford.
The engine already has cleaned up heads and valves, adjustable cam pullies (cam timing set i.a.w Brad Black's article a lightly modified Senna map, Piper foam filters in the intakes, Termi silencers, standard but cleaned up internally exhaust (man, you should have seen some of the welds from the inside!!!). The focus, engine wise, has been on making the best use of what I have.
After some study and a great deal of though I have the beginnings of a plan. Amongst the books in my library is "Design and Simulation of Four Stroke Engines" by Dr Gordon P Blair. On p527 onwards ther is a study of the Ducati 955 racing engines. The study notes the pressure wave differences in the exhaust and inlet tract and suggests that this is due to the L-twin arrangement. The study does not comment on how to change/modify these differences to improve the engine.
Putting it simply the vertical cylinder is not optimally set up. The study suggests the exhaust arrangement is the root of the problem. I would suggest the throttle bodies also play a part. Most engines have the butterflies open so that the edge of the butterfly at the top of the port rotates towards the body intake. This helps direct flow over the bottom of the port at part throttle and slightly so at WOT. On the Ducati arrangement only the horizontal cylinder works like that. I have often wondered what the real world effect of this would be. I was tempted to think "not much if Ducati thought it was OK" but then I remembered that initially Ducati didn't use the offset map for the horizontal cylinder either.
As I have a spare set of throttle bodies I was thinking of cobbling up a set that made both open "the right way" to see if/what difference there is. Or I might go the whole hog and get a suitable set of bodies to modify in this way but use pico type injectors if my 900SS/Monster throttle body swap gives good results.
Together with this I have three different sets of bellmouths. 748/916, ST4 and 996. My preference is the ST4 bellmouths. It has occurred to me to experiment with an asymmetric arrangement using the good Dr Blair's book as a guide.
Before I jump down this particular rabbit hole I would just like to ask, "has anybody out there been here before and if so what were the results"? Don't worry, you are unlikely to meet me on a race track
.
The engine already has cleaned up heads and valves, adjustable cam pullies (cam timing set i.a.w Brad Black's article a lightly modified Senna map, Piper foam filters in the intakes, Termi silencers, standard but cleaned up internally exhaust (man, you should have seen some of the welds from the inside!!!). The focus, engine wise, has been on making the best use of what I have.
After some study and a great deal of though I have the beginnings of a plan. Amongst the books in my library is "Design and Simulation of Four Stroke Engines" by Dr Gordon P Blair. On p527 onwards ther is a study of the Ducati 955 racing engines. The study notes the pressure wave differences in the exhaust and inlet tract and suggests that this is due to the L-twin arrangement. The study does not comment on how to change/modify these differences to improve the engine.
Putting it simply the vertical cylinder is not optimally set up. The study suggests the exhaust arrangement is the root of the problem. I would suggest the throttle bodies also play a part. Most engines have the butterflies open so that the edge of the butterfly at the top of the port rotates towards the body intake. This helps direct flow over the bottom of the port at part throttle and slightly so at WOT. On the Ducati arrangement only the horizontal cylinder works like that. I have often wondered what the real world effect of this would be. I was tempted to think "not much if Ducati thought it was OK" but then I remembered that initially Ducati didn't use the offset map for the horizontal cylinder either.
As I have a spare set of throttle bodies I was thinking of cobbling up a set that made both open "the right way" to see if/what difference there is. Or I might go the whole hog and get a suitable set of bodies to modify in this way but use pico type injectors if my 900SS/Monster throttle body swap gives good results.
Together with this I have three different sets of bellmouths. 748/916, ST4 and 996. My preference is the ST4 bellmouths. It has occurred to me to experiment with an asymmetric arrangement using the good Dr Blair's book as a guide.
Before I jump down this particular rabbit hole I would just like to ask, "has anybody out there been here before and if so what were the results"? Don't worry, you are unlikely to meet me on a race track
.
