I really enjoy taking the bike to the dyno. It’s so useful to see the results of changes prior to driving 300 miles to a race circuit and it gives you a deadline to get things done by.
The rolling road dyno I use is at Alan Jeffry’s engine tuning workshop on the Valley road in Plymouth. Alan’s a really nice guy but the main part of his work is cars so the motorcycle dyno is run by GT motorcycles (01752 485000). A single run (at time of writing) costs under £40 including VAT and Steve, who operates it, is a two stroke fanatic and a very experienced re-builder and tuner. He had an NSR 500 (GP bike) complete with carbon chassis on his stand when I saw him on Thursday. People with NSR 500s aren’t going to let just anybody work on them.
It was all the more enjoyable since I was joined by Roger who, having made the journey down to Devon to meet his new grand-daughters the day before, was interested to see the improvements I had made.
I was there at 9.30am as planned, and then again at 9.45am… this time with fuel!
As I said in the Beezumph report post, it didn’t feel any quicker to me in the way it was delivering power, but I thought that it was pulling through a higher rev range. This wasn’t actually the case since it is producing more power, in fact it’s almost exactly doing what I intended to do when I started planning the modifications at the beginning of this year.
The plan was to try and get the engine to breathe better with some carefully executed gas flowing and port modifications, and also to extend the inlet timing a little to see whether I could take advantage of any negative pressure pulled by the exhaust before the transfer closed. By using Jennings’ port time/area calculations I was trying to move the peak torque up the revs a little from the previous 3500RPM (ish) to nearer 4000rpm. I didn’t want to lose the bottom end and I knew that was too easily done.
See the graph below. The blue line (as indicated) is last years test after returning from the final Cadwell park BHR meeting.
How that translates into horsepower:
So, it shows that there’s a fair bit more power available and really well spread over the rev range. It may be that that’s why it didn’t actually feel more powerful, because it delivers it so smoothly over the range.
Whilst peak torque is up from 31.8 to 37.9 ft/lb (almost 20%), it’s interesting to see the change in revs that this occurs at. Previously it was around 3700 RPM and now it’s pretty much dead on 4000 RPM.
Also, driving out of corners should be much improved as low down torque is significantly better. I haven’t plotted the actual revs through the gears at corners for Cadwell, for example, but for slow corners like the Old Hairpin and the chicane after Mansfield this is where you really need that low down grunt, otherwise you get passed on the exit. At 3000 rpm, the torque is up from 23 to 31ft/lbs (35% increase). That’s pretty impressive to me.
So extrapolated from that, the peak power is up from 26 to 33hp, but still everything stops at 5000RPM. Steve said he could feel it wasn’t producing any more so he just shuts down. Whether it would actually rev any more anyway is another question. Unfortunately I have no idea what I am revving to because my Scitsu hasn’t worked since I converted to methanol. Apparently a common problem with inductive rev counters due to methanols highly conductive nature. Something I need to address sometime.
The main focus now is to fit the twin carbs to give me more intake mixture. The 30mm carb is definitely sized small and
I’ve got less than a month before the last Cadwell (27th and 28th September). It may well be that this will keep things going up toward the higher end of the rev range where the need for an easier ‘gulp’ comes into play. It may be that it loses some immediate pick up at low revs, but we will just have to see.
The other thing that I need to look at is the cylinder head. I’ve never worked on the head, it’s a standard ‘MOSS Engineering’ high compression head which is designed to raise the compression to a level acceptable on a fast road machine on petrol. Since I’m on methanol, I can deal with some extra squeeze and with a bit of time and effort I think I could get the compression a bit higher which would increase the burn speed. I’m then looking at 40 ft/lb as possible and maybe even a fraction more. I may even extend the rev range a little.
Ideally I need to get the work done in time to get to the dyno again before I go. Just over three weeks.. I’d better get a move on!