There’s a strange thing happening at the BSSO scooter racing in 2016. It seems that ‘small’ is the new ‘big’. More races this year have been won by engines based on the 125/150/175 kits than those for 200 casings. What is going on?
Ten years ago Group 6 – the top British class for ‘special’ scooters was dominated by elaborate water-cooled Lambrettas built to maximise engine capacity and torque. Often the engines were so heavily-welded that it was impossible to tell which cylinder kit the barrels were based on, but in almost every case the answer was Terry Shepherd’s venerable TS1.
This year, things have changed and we have the leading contenders from both Replay Racing and Casa Performance both racing small-block engines.
Darren Conneely’s machine built by Chalkie of Replay Racing runs a Super Imola on Spanish 150 casings. As standard the Super Imola is like a small-block version of the Super Monza, complete with sub exhaust ports. As standard this 66mm-bore kit is only 200cc but Chalkie has developed this to run with a longer 64mm stroke crankshaft giving almost 220cc.
Similarly Casa’s leading rider in the championship this year is Luca Zani and he’s running a Casa SS200 kit on a 150-stud-pattern version of the new CasaCase. At the start of the year this engine was running on a stock 58mm stroke crank giving only 200cc and around 30hp. Since then the Casa scooters have been returned to Italy, re-tuned the small-block is now producing around 39hp from a 198cc engine. That lack of capacity hasn’t stopped Zani from having a long winning streak and taking the outright scooter lap record for Cadwell Park down to 1:48.
Change of direction
We at SLUK wondered why the current top teams had switched tack from big-bore watercooled-bangers at the class capacity limits, and instead adopted high-revving air-cooled engines.
There must be more to it than simply having cheaper casings to use.
There are some theoretical advantages. Smaller-bore cylinders (made from the same moulds) actually offer more transfer port area as a percentage of the bore. Smaller bore kits have more space between the piston and the reedvalve, reducing obstruction to the boost ports. Also the slightly longer transfer ducts of a smaller bore barrel can be better used to direct the fresh gas more precisely. Ordinarily you’d expect these benefits to be offset by giving away engine capacity. Zani’s engine could be 60cc bigger and still within the Group 6 class limits.
For Chalkie though, it is to do with a shift of mindset. Previously tuners concentrated on big capacity, big-torque engines to pull tall gearing, now the pendulum has swung the other way.
“Where people set out to build old engines that pull tall gearing and might get to 115mph on a straight, we set out to build an engine that would get to 100mph very quickly and had enough over-rev to go a little faster. Getting up to speed quickly and holding it is better than taking time to reach a higher top speed.”
Chalkie did his first small-block experiments with Steve Conneely’s ‘chain-saw’ in the 2015 season, which was a small-block Group 6 machine that used a long-stroke RB20 cylinder.
One of the chief advantages is in ease-of-use, because a higher-revving small-block engine doesn’t deliver the same vicious kick that you get from the lower-revving large-capacity motors. Depending on exhausts, the screaming small-blocks actually tend to be gentler to ride.
Other tuners have found the same phenomenon. Alex from Cosmoto prepared a small-block Super Imola for his previous racing exploits, while the Casa Lambretta team have long had success with the SS200. The key seems to be in getting the engines to rev, which allows the engine to work over a wide range of speeds in each gear.
“There are advantages to using a smaller, lighter piston,” explained Chalkie. Certainly you can rev them higher with fewer reliability problems, though Replay have had issues with the drive side main bearing spinning in the casing and destroying the Hallite washers that they are sandwiched against.
When we shot the video (above) early in the season at Mallory Park, Chalkie set up Darren’s engine to rev to 10,000rpm, but for the forthcoming Lydden Hill meeting he has liberated a few more horsepower (now also ‘over 40hp’) by getting the engine to rev on as far as 10,900 rpm with peak power produced at 10,000 revs. Similarly the Casa SS200 of Zani got a mid-season tune-up and can now be revved to 10,800rpm!
Unless something unexpected happens it looks very much like an air-cooled small-block engine will win Group 6 this year, and that completely contradicts the old mantra of ‘there’s no substitute for cubes’.