How time flies …. For various reasons I have not run the bike since 2021, one reason being somewhat disappointing dyno results, another me spending a lot of time transplanting my tuned ST2 motor into the SSie frame of our rain bike.
2022-05-08 11.05.13 by
torbjörn bergström, on Flickr
It´s almost the same motor, but a lot of small things that should fit, didn´t without modification of some sort, like the rear header that suddenly interfered with the new crankcase:
20220215_154120 by
torbjörn bergström, on Flickr
However, most time consuming was adapting the ST4S loom to the bike, in order to use the Nemesis / Microtec ECUs on the bike:
20201027_154413 by
torbjörn bergström, on Flickr
In the end, the bike was ready for the start of the 2022 season, and I ran it at some track days thru May and June, adjusting suspension, and doing some on-track mapping. Unfortunately, during one such session, an overly enthusiastic Aprilia V4 rider decided to overtake 2 riders behind me at the end of the main straight, forgetting about the 90° right-hander at the end of the straight. Further, instead of taking the escape, he decided to try making the turn, but only partly managed the turn, but managing very nicely to torpedo me just exiting the turn. The ones he overtook estimated the speed differential to be something like “at least 70 kmh”, I just remember a dull “thud” and suddenly seeing my own feet against the sky.
All things considered, it ended far better than it might have, but the bike needs quite a bit of repair work, and I spent 2 nights in hospital due to some diplopia. I was subjected to al sorts of head scans etc., but the found nothing, whatever that might mean …
2022-07-09 10.48.32 by
torbjörn bergström, on Flickr
2022-07-04 14.20.38 by
torbjörn bergström, on Flickr
Anyway, this left me with just the M800 to ride for the rest of the summer.
So, back to the HYM1100. After the track day season, I did get to dyno the bike, first with the Proservice / 50 mm TB combo, then (due to disappointing results) with the Biggelaar heads and stock TBs (with slightly less, but still disappointing results).
HPD1100 power by
torbjörn bergström, on Flickr
I do not have an explanation for this, other than that the various parts thrown together did not harmonize very well, and that I had turned the piston tops down slightly to lower compression a little. Which does not really explain the dyno result with the Biggelaar / Stock TB results, which were markedly worse than last time.
One thing that I can notice is that the torque curve is “wavy”, with a low point right where max power occurs, at about 8000 RPM. Running the bike with just the headers increased power by approx. 6 HP, so there´s something to be had by getting inlet and exhaust systems work im harmony with the rest of the motor.
At that point, I decided to not run the bike again until I had the downdraught heads on the bike, and that is now my main aim for the coming winter.
For reference, below some flow numbers as measured on my flow bench:
HYM_DS Flow measurements by
torbjörn bergström, on Flickr
On might think that the heads with the higher flow numbers would yield the highes power, and in an "optimized" combo the highest flowing heads might well have the highes power potential, but in this case it did not turn out to be the case. In fact, the "best" heads (Pro-service) with the biggest (50 mm) throttles turne out to show the lowest power on the dyno. It´s important to remember that the flow bench can only tell you what is most, not what is best. At least I hope that I have learned someting from this that I can use later.
However, since I did not want to torture the M800 for another full track season, I decided to get the HYM motor running again. Which, hardly surprising, turned out to be more work than I had anticipated.
Last winter I had the Biggelaar heads skimmed 0.5 mm, in order to get a more squish-band type of combustion chamber:
2023-05-24 16.31.25 by
torbjörn bergström, on Flickr
This, in combination with the Pistal pistons, gave a CR of about 13.5:1, which I found a bit over-optimistic. So instead the stock pistons were dug out and adapted; to get a decent CR, I decided to delete the base gasket, but this in turn necessitated the valve pockets to be machined for clearance. It also necessitated machining the squish part of the piston to get the proper squish clearance. In the end, the CR is somewhere slightly above 11:1.
2023-06-18 13.22.18 by
torbjörn bergström, on Flickr
I had also intended to test the ByThe cams, but that did not work out; after I had ground the closer shims down to get 0 closer clearance, I had 0.6 mm opener clearance with the thickest opener shim I had. So that will have to wait for the next stage 😊
While I was at it, I did some re-shaping of the combustion chamber, basically as a “de-shrouding experiment”, checking for changes in flow numbers as I went. I did see some slight improvement when opening up the chamber slightly on the “outside turn” side, but also some loss while opening up on the cylinder wall side of the chamber, behind the inlet valve so to speak (where the modeling clay is in the pic):
2023-05-29 15.13.45 by
torbjörn bergström, on Flickr
With all said and done, I ran the bike at the latest track days. Due to rain and slick tires the first day was all M800, and the second day was mostly spent mapping to get the bike to run properly. The map I stared with was pretty OK at high load / WOTish load, but awful in the off-throttle/on-throttle situations, making exiting turns pretty awful. However, by the last session of the day, I´d managed to sort that pretty decently, and the last turn of the day was a real joy. Sooo nice to ride the bike in at least slight anger again. I´m looking forward to the next few track days.
Kind regards,
Torbjörn.
