So who is doing what about increasing capacity? Which of the new casings take the longest stroke crank and the biggest diameter bore?
I've got a 262'ish cc Mugello, running a 65mm stroke crank and 72mm bore, however the fundamental restrictions of casing meat for stroke (+ web width) and cylinder spacing for bore always become the constraint What I'd really like is an air cooled motor running a 70+ stroke crank and 75'ish mm bore (309cc).
I'm not interested in revs and powerbands, just a thumper that I can climb wall with and gear for a relaxed touring speed at low RPM.
Adam_Winstone wrote: ↑Mon Nov 27, 2017 10:54 pm
Hi all. What I'd really like is an air cooled motor running a 70+ stroke crank and 75'ish mm bore (309cc).
I'm not interested in revs and powerbands, just a thumper that I can climb wall with and gear for a relaxed touring speed at low RPM.
Out of interest...if you could achieve any (realistic) power delivery, can you describe what is your ‘holy grail’?
I’m looking for specifics....
1) Peak bhp
2) Peak ft-lbs
3) Where (rpm) power would start, peak and rev-on until
4) What cruising top speed would you desire
5) What terminal top speed would you like to achieve at over-rev (for blasts and overtaking etc)
6) What gearing would you like to pull
If you could answer those questions, then I think the component list (and port time-areas) are readily available...with or without ‘more cubes’.
I would doubt that what Adam is looking for is available at the moment as unless I'm mistaken, the main issue is revs. Personally I find cruising at around 5k RPM the most comfortable, so if I had a motor that could shove me along at a genuine 70mph at 5k rpm I'd be very happy. I think current offerings could give the performance easy enough but at 6-7k rpm which I would not find relaxing for a prolonged motorway thrash tbh.
So, what motor will currently pull a TV200 18/47 to cruise at 5K and continue to pull to 6-7k when desired? You can probably answer the rest of the questions yourself, i.e. what BHP and peak ft-lbs do you need to do that whilst meeting these criteria. If you can answer that then you'll have answered your questions and provided me with the answer that I'm looking for... yipee!
Peak BHP = Don't care, providing it pulls the gearing correctly then I don't care if it makes 16bhp.
Peak Ft-lb = again, not too concerned about peak' I'd be happy for it to flat-line across the board at a reasonable figure.
RPM = Most of my current road motors start to pick up really well from 5k so it would need to better that. 3k would probably be fine.
Cruise = Same as my road speeds in a car, anywhere between 60 and 80... at next to no revs.
Top speed = 85-90mph would suffice.
Gearing = 4.5 - 8.5k (max) RPM, whilst returning those MPH figures. Edit: let's drop that to 7.5k max as 8.5 is too close to what we already have.
I can do any of these in isolation with many of the motors already on the market but I can't do all of them with any one of the motors on the market. I already have motors that will cruise at 60-70, I also have motors that will do 80+ (one of my motors doing 80 on the 1/4 at Pod and 96 on the dyno), all of my motors can do 5k RPM... unless the stator is failing (LOL).
I've had a nasty blowout and a layshaft shear so I don't plan on belting everywhere at 70+ but I would be quite happy knowing that I can go as fast as I like, as and when I feel like it, without needing to upgrade everything massively to cope with high RPM stress.
Tuning is great but typically you lose at the bottom what you gain at the top. However, take a 125 and bore it to 150 and you end up with a faster bike that has a much better spread of power and, geared correctly, a higher top speed for perhaps even fewer revs. 150 to 175, same applies. 175 to 190/200, same again. 200 to 225, bingo, we're getting there and really motoring. 238 / 240 / 250 / with mild road porting and you've got a bike that is a pleasure to rally on, whether you be 20 stone, 2-up + luggage, etc. This is tried and tested, with me having small block pistons up to 66.4mm and large block up to 72, with 60, 62, 64mm stroke cranks, all of which are common place. I'm just wishing that the small block to big block progression that Innocenti gave us would have been carried on to the 'bigger' block step.
You can achieve pretty much all of this using a p200 case, Polini 210 ali/nicasil kit with 60mm crank, a 28 or 30mm carb & 24/63 up gear kit...
Reliable early 20’s hp & similar torque figure... low revving & torque laden, making power from just over 3k rpm & peaking @ 6.5k... will cruise comfortably @ 70mph pulling just 5 - 5.5k rpm and capable of a genuine 80+ mph top speed.
Reed valve it & widen the ext port by around 1mm & it’ll add another 1k rpm to the rev range pushing peak power up to around 25hp whilst retaining that mid range grunt.
Only one snag...... it’s a Vespa!
Burgman... yes it would, because it is a 400cc, hence my desire for more cubes, rather than straining the cubes that I've already got.
Nowt wrong with Vespas but the tuned ones that mates have had end up having all of the same failings that Lambrettas of a similar size end up with. Even so, note what you've done to provide that performance... bigger cc by bore and still bigger cc by stroke... Cubes, cubes, cubes!
What I'd really like is an air cooled motor running a 70+ stroke crank and 75'ish mm bore (309cc). 
