BI G THUMPER TECH SPEC – A WORD WITH THE EDITOR

Having heard good things about Stu and the scooters he was working on, as always, I wanted to get to the nitty gritty of what he was doing with them in technical terms. We had an initial conversation about his history in engineering, how he moved into the world of scooters, and it became obvious that Stu hadn’t reinvented the wheel… more like, stripped it down, taken a long look, had a bit of a think, bought some quality spokes, and rebuilt it to engineering standards, with the consumer’s end use in mind. It would seem that this ethos has been the foundation of how he approaches scooters, and it certainly seems to be working for him.

Not from round these parts are you?

It’s always interesting, to me anyway, when someone outside of the scootering fraternity delves into the scooter tuning/ building scene… as what has often been overlooked for many years can become very obvious when someone else points it out. Or conversely, ideas which have become entrenched in scootering folklore (we must use this part like this, and that part like that) are not utilised, because the person executing the build has no concept of them. The only caveat to all this, is that scooters can be very unique in their set-ups. There are many nuances to each scooter and the individual component for them on the market, how they interact with other components, and scooter owners tend to learn this stuff inside out: this pipe works well on this kit, but not on that kit, or info on routing fuel pipes and header pressures on Vespa petrol tanks… and so on. In these instances, prior scootering knowledge is something which comes in very useful. But it doesn’t take long to learn many of these things, especially as an owner/ rider/tuner.

By his own admission, Stu has hit a few snags… but more importantly, his analytical engineering background has proven its worth, and you can see this in his interview quote: “Make a change, prove it, and move on to the next. Obviously there are always the occasional snags, but in recent years they’ve become much less common, and you have to learn from them”. That to me says two things: 1) His tuning steps are methodical and logical. 2) His errors are noted and addressed. That’s important.

What’s going on inside?

So the big beast, all 261cc of it… what has Stu done to get the rip-snorting performance to this level? Well, quite simply, he has made a good selection of components, which work well together as a complete package, and assembled them to engineering standards. He is using Pinasco casing to overcome the well-known problem of standard P-range Vespa casings cracking like the San Andreas fault line, a Quattrini 232 kit as the powerhouse, a Kingwelle 64mm crank to get the big-cc capacity, and a DRT clutch and gearbox to distribute the torque. Top this off with a standard Piaggio ignition (K.I.S.S.) which has had the standard flywheel machined and set to 17 degrees BTDC, a 38mm TMX and a relatively unknown German pipe brand… and there you have it, quality components put together correctly. Pressure tested, dyno tested, road tested… in that order. By his own admission, it’s still in development, and from what he told me the port timings still need a little tweak in order to get the best from the setup, but it sounds like he’s on the right track.

The power?

Well, according to Stu, even when riding ‘off pipe’ (this means before the main power band kicks in) on his dyno it is reaching 20bhp at around 4500rpm, the main surge of power starts just before 5500rpm and it builds until it peaks at 40bhp around 7500rpm and holds the peak almost flat until 9000rpm, before finally dropping off! In his own words “I try to produce engines with broad power bands, which will pull gearing”.

Well it certainly appears that he is managing it. Already GPS’d at 94mph, once the fuel pump issue is resolved, 100mph could well be achievable. Stu remarked: “I’ve done all the calculations and wind drag models on the computer, the ton shouldn’t be a problem once I’ve got the fuelling sorted.” While the 261 is his own play thing, the 232cc engines which he produces for customers are knocking out 20lb-ft of torque all day long, and seem to make the perfect mile munchers. It’s good that he is pushing the boundaries and developing the crazy stuff for himself, and then utilising the info to provide powerful, reliable and more sedate models on the road for his customers. If and when he cracks the ton, we will let you know.