Hats off to you mark parker. Nice work and documentation so far. I've really enjoyed this and it has given me impure thoughts for my Norton 750 USS rebuild.
As for Mr. acotrel.............
acotrel wrote:I have a couple of questions :
acotrel wrote:Who has got the fastest road race 750cc Norton in America ?
I do, I do ..............well at least I thought I did until the last engine fragged on the dyno - it was ready.
acotrel wrote:Is their bike setup to develop high horsepower at high revs, or a lot of midrange torque at moderate revs ?
I hope I don't disappoint you acotrel as this has been covered for you several times before but the answer is yes to both - high hp at high revs and a lot of torque at mid range revs. The engine is a 75mm stroke with 12.6:1 compression ratio. It gives up virtually nothing for mid range and has an extra 1,500 to 2,000 rpm of additional torque and power.
acotrel wrote: And how is their bike geared for most circuits - high or low ?
Think about what you are asking here..................the bike is geared like any other race bike. Gear for the longest straight and then maybe tweak it a little if you think you can gain on infield turns. I am running a six speed with this 750. Keep in mind that this is no longer your garden variety long stroke Norton, gear accordingly.
acotrel wrote:I suggest that what happens in the inlet and exhausts of a four stroke motor happens under sonic conditions, so when you use a low velocity flow bench - what you see might not necessarily be what you get when the motor is operating.
Did you mean to say super sonic conditions as in sonic choke? I do agree that flowing a port at one pressure differential only is not the complete picture but it is one hell of a good start. Professor Gordon Blair (and others) made a case for flowing both the intake and the exhaust at multiple different (and considerably higher) differential pressures so that you could develop a map of the port behavior. Professor Blair also made the case for flowing the ports in reverse as this is what happens during overlap. All this data was then used to simulate the performance of the motor.
acotrel wrote:When you widen the inlet port each side of the valve guide, you might be kidding yourself. A change of direction at that point might induce swirl and upset the standing wave and reduce the mass transfer in the port when the motor is revving fast.
You might be kidding yourself if you think a fixed cross sectional port is going to behave well when you stick a valve stem and valve guide in the pathway which forms a constriction in cross sectional area. Furthermore, please explain or illustrate what a "standing wave" is and how it pertains to our beloved Nortons. You can use flip charts and wave your arms around if that helps.
acotrel wrote:As far as XR750s putting out 100 BHP - on whose Dyno ? As I understand it, most of the dynos which are inertia based give results which are all comparative to the Yamaha Vmax, and a nominal horsepower value for that motor is used to set the fiddle factor. When the 500cc Manx Norton turned out 50 BHP, it was probably measured on a Heenan and Froud test brake from first principles. Are you telling me that the XR750 turns out twice the horsepower of the Manx ?
Let's put the discussion of comparative dynos to the side for now. A post 1989 XR750 is stinking fast. We've competed against the XR750 and there is that big difference in raw power. I would say the 100 BHP is real though I have never done a dyno run on one. The 500 Manx Nortons of today are closer to 60 RWHP. A post 1989 XR750 redline according to the HD factory service manual is 9,200 rpm whereas a well sorted out Modern Manx Norton short stroke is 8,600 rpm so not only is the XR 750 sweeping 50% greater volume but it is capable of doing it at a greater rate of speed.
So (Manx 60rwhp) X (9200rpm/8600rpm) X (150% swept volume diff) = 96 RWHP for an XR750...................allow say 4 hp for friction loss and you have an easy 100 BHP