|Gilera 50 Touring, somewhat modified by my brother, and later further
modified : 19 inch frontwheel, Paioli fork, adjustable rear shocks, gauge cluster.
Simonini 50 cross, 11 hp, lightweight racer.
|Honda XR 75 with Honda TL 125 suspension - used as a stuntbike !
Very red !
Jincheng Monkey.... modified suspension, 10 inch Dax rims on billet centers,
and sticky tires.
|First tracktest, 39 year race in Linköping. Every imaginable error
turned up here, pursuing fuel delivery problem all weekend. No fun!
Shredded Blower drive belt replaced! Lower fouthgear needed !
Specification : Honda CD50 engine in modified Fantic Caballero frame.
Front and rear suspension travel reduced, 1.5 and 1.6 Borrani rims
with Bridgestone tires, steel tank and seat.
Weight without fairing 64kg.
Engine specs: bore x stroke 38 x 41,4
lightened crank, polished conrod, stock piston C.R. 8,8:1,
CD50 head, ported w. stock valves, stiff valvesprings, SS50 camshaft (5,25 HP)
26mm Keihin w. #140 main jet, 30%underdriven Bendix vane- pump, 28mm Id exhaust
Kitaco inner rotor CDI, C8hs sparkplug, SS50 dualdisc clutch, stock 4speed trans
Rpm range 8500- 12500.
End of season 2004!
|2005 season: Got required licence for classic roadracing at Vandel, but due to exceeding the
noiselimit by 2db´s ?, it almost did´nt happen. A spectator and Big Honda- fan came to my rescue,
offering his CBR1000F roadbike. What a bike! What a guy! Thanks again.
Later at an evening training session at Ring Knutstorp, the bike holed a piston at end of straight
The search for a colder sparkplug was intensified. Old sixties Honda plug chart showed a
raceplug- range between C10s- C14s.
A handfull sparkplugs was received just before leaving for a test-and-tune session in Leipzig.
Leipzig proved that turning a moped engine into a raceengine isn´t an overnight deal.
New problems surfaced, a departing, at speed, belt-tensioner and later an exploding clutch
shortened my races. Lesson : Always put the tensioner on loose- side of belt !
|Reconstructed the supercharger drive, remounted carb, and made a smaller plenum, before the
40year- race. The idea was to shorten the drivebelt, reposition the tensioner, and shorten the pass
of mixture. Testing on rolling-road, showed progress, but boostnumbers still hovered around 1.3bars.
Turning the supercharger slower wasn´t possible due to space limitations, and new palm-sized Roots,
were not in sight. With piston crown reduced, and chamber somewhat enlarged, C.R. was lowered to
8:1 leaving combined C.R. above 13,5:1. Not good! Premium fuel, retarded timing, and a 20mm
Keihin did lower boost a little, and I must say, improved driveability. Rolling road test reveiled a wider
torque- band, 8000- redline, and then some. Rpm limiter wanted ! A lower 4th gear were installed in
2 engines, and as per recommendations, a front engine support, to reduce flex and missed shifts.
In Sweden, the increase in torque meant that I hit redline, just into the straight, and before I
could do anything about it, the supercharger seized, snapping the drivebelt immediatly. In timed
practise, the engine started to feel rough, and I headed for the pit once more. Metal shavings in
the oil meant disaster, and later a well chewed cam- chain tensioner wheel, reveiled itself. Managed
to get ready for the main race, The spare engine sounded real good, and the last supercharger turned
freely. I felt good about it, but during the warm- up lap, I lost two gears, first and third. Start
in second, and up to fourth, slower acceleration than normal, but not much! The engine pulled like
never before, and I actually gained on the twostrokes ahead, it pulled hard on straight and reached
12700rpm in topgear. Half a lap later I ran out of fuel !!! Blamed the pit crew offcourse.
With present gearratio, that equals to 142 km/h, an okay speed for a stock- cammed moped engine
with a little boost!
End of season 2005!
|Picture at left shows the new improved silencer/megaphone for the Honda.
Exceeded the limits last time out so an update were needed.
When compared to the usual method: rolling several cones, welding them individually,
and then piecing them all together,
hydroforming is a clean way to shape a silencer, and faster too.
The technique goes like this:
The Honda CD50 engine is with its 39x 41,4mm and a single cam, not exactly what you would call
a high winding screamer, but nonetheless chosen because its cheap and plentifull. A plethora of
speedparts exists for this engine- family, due to the fact it has been in production since 1965,
and still is!. But most tuning equipment concerns increases in cc´s, mostly done by a bigger barrel:
a 51mm barrel and piston can be fitted without modifications to the crankcases giving 80cc + with
The challenge for me was raising the power- level without exceeding 50cc and a supercharger
enhancing midrange torque, keeping this longstroke- engine revs at a sane level.
Collected a lot of different small superchargers and realized that all of them were oversized for
the job, but I managed to reduce one by two- thirds by cutting and welding. With a 3: 1 drive ratio
this blower gave ½bar of boost at 8000rpm - perfect for a start.
And this year I got an opportunity to try out the new combination, as a big classic racing event
were scheduled at one of our oldest tracks here in Denmark. Hastily a lot of small improvements for
the bike were planned: 35mm lowering of the bike, stiffer rear shocks, seat moved 100mm rearwards,
and a more efficient silencer.
The weather were perfect for this time of year, and the track was different from what I have tried
before. I would call it a four- stroke track, as the strong engine- breaking made my Honda drift
into the corners, helping to a tighter radius. Some two- stroke drivers were surprised by this
luring track, with its blind corners, and some did outbrake themselves into trouble.
I was lucky meeting up with another Honda driver, Dutchman Wim Heeroma on his fine 89cc Dream
50r, who challenged me throughout the weekend. His relaxed driving- style gave me an advantage in
the corners, but on straights he would gain on me - fantastic! All Saturday I kept the 3:1 ratio on
the supercharger drive, but in the evening Wim told me he would remove all silencing from his
megaphones for Sunday, and by that gain 10% in power! Wim new what he was doing - that old fox,
immediatly I increased the supercharger drive to a 2,5: 1 ratio which raised the boost from ½ to
1bar. That resulted in a 3second gain/ lap and Wim couldn't equal that speed.
But from experience I know that 1bar is close to the limit on these engines, and quite surprised
when the engine went through Sundays training without complaining.
Feeling confident before the race about this bulletproof setup, until the engine let go on the
warm up lap - like so many times before.
End of season 2008
Specs for the 2008 season:
Honda CD50 engine 39,25x 41,4mm, severe ported standard head with standard sized valves,
stronger valve springs and a SS50 camshaft (from the 6.25hp model), sectioned Aisin AMR300
Roots style supercharger fed by a 20mm Keihin, oilcooler, standard four- speed transmission
with a reduced fourth gear, and an aftermarket clutch (not crank- mounted like original!)
Guesstimated horsepower: ½bar ~8hp and 1bar 9½hp at 13000rpm. Redline: 13500.
Usable torque range: 8000- redline.
|Watch this bike!|
|Before the 2009 season (read: a single race meeting in Sweden), I had used most of my spare time
finishing the Kreidler racer, but a quick fix for the Honda was needed! A thorough search for a
preferable forged, low compression piston, had come up with nothing, so plan b was activated.
Honda made a lot of 50cc engines with different bore and stroke combinations and the P50 had a
flattop piston with the right pin- size as well as pin height. But, coming from an engine with
a larger bore meant I had to exceed the 50cc volume by a whisker - don´t tell anyone!
|With the P50 piston installed, a compression ratio of 6,2: 1 was reached. So far so good!
That meant ignition timing could be sligtly advanced but by using a flattop piston, the squish-
band was disturbed, and I expected some kind of counter- reaction. Normally a dished- piston would
be the better choice, but time didn´t allow such tests.
About tests, I have plans for thorough testing through use of an engine- dynamometer. An
invaluable tool that allows you to connect every imaginable instrument (a thing you possibly
cannot do during track-testing!), and recently I purchased this Heenan-Froude DPX0 water-
brake. This tiny table- top dynamometer, handles engines with outputs less than 60hp and
thus covers my current need. The similarity in design of the Honda CD and Kreidler engine
will simplify the mounting of engine on dyno.
Planned for 2010..or 2011:
Modifying crankcases to house a 6- speed transmission.
Test of a special- made piston of the flattop- variety, reducing CR to
6- 6,5: 1!
Build- up of a 50cc four- stroke twin.
|Twin- project is on the move - slowly that is. Bore to bore distance had to be decided before moving on, and now everything fits. Height of cylinder is dictated by: conrod length, and index of camchain.
Engine specs as of september 2011:
CD50 crankcases widened 50mm, bore&stroke of 35x 26,5mm, rodlength 60mm c- c, siamesed CD50 heads with SS50 cams, CR80 six-speed trans and clutch.
Contemplating a more historical correct standing- cylinder layout.
|Update on the Honda:
The last two outings revealed that this rev- happy engine must be kept below 12500rpm. Following that practise, and the damn things drives through it all! Tried another mix of race- gas and had no signs of knock with a 1bar boost setting - all good!
Looking forward to the next session :o)
Last race this season and again no sign of pinging - time for an increase in boost!
Increasing the boost necessitates an alteration to the ignition timing, to decrease the ever present danger of detonation. I have attached a chart showing the curve built into the Kitaco inner rotor ignition mounted. As you can see it just keeps on advancing. And no boost retard. I have been running this curve all these years knowing it was no good for a supercharged engine! The only reason for retaining it was lack of time and mechanical trouble elsewhere :o)
Raising boost means increased combustion- pressure, and a weak point in supercharged engine is the head- gasket. A simple mod is o-ringing - a groove is cut into the face of head or cylinder, and a stainless steel wire is inserted. This wire must be placed just outside of the head gaskets compression- ring, protrude the surface no more than 25% of gaskets thickness.
Why choose supercharging ? Well, if I had learnt one thing, when playing around with engines, its the fact that rpm kills ! Always choose the engine which produces its peak power,as well as torque, at lower revs.
A high winding screamer engine sounds fantastic, but not for long!
Supercharging will boost any engines midrange to a degree, that you automatically short- shift through the box! Adding a rev- limiter will save your engine in case of a missed shift.
I can sum up the differences between conventional tuning and use of supercharging.
If i should extract maximum horsepower from this Honda CD 50 engine using a conventional approach, i would need following parts :
A big- port cylinderhead with biggest possible valve-sizes.
A camshaft timed for operating at high revs which also lifts the valves further, again to maximise airflow through the engine.
A high compression piston, if available, or decreasing combustion- chamber by shaving head.
Then a very strong and well- balanced crankshaft assembly, outfitted with top-of-the-line C3 bearings, to handle the much higher than standard revs.
An optimised oiling system, including oilcooler.
The result would be an engine with a very narrow rev- range, like 10500 to 140000 rpm, necessitating a very close- ratio gearbox with at least 5, or even better 6 speeds.
Horsepower figures around 8- 10.
In supercharged form, far from fully developed, this engine produces 10- 11 hp and a usable rev range of 8000- 12500.
Only non- original parts sums up to be cdi- ignition, hi- volume oil- pump, stiffer valvesprings and an upgraded clutch.