We investigate the technology behind a GTS 300 that really deserves to be called “Super Sport” as the quest to crack 30bhp in Austria continues…
Words and photos: Boris Goldberg
Tuning traditional two-stroke Vespas is currently going from strength to strength – new kits, crankshafts and other goodies are hitting the market literally on a weekly basis, allowing for bolt-on performance that only expert tuners could have expected to reach a couple of years ago.
Quite to the contrary is the situation when you look at four stroke Vespas. In most cases, tuning here means fitting a ‘sports’ CVT and an aftermarket exhaust, which might boost noise levels, but generally does little for performance. Very rarely people venture into barrel and piston kits, let alone think about altering valve timing, cams and playing around with injection systems.
The reasons are rather obvious: the GTS offers a very reasonable level of performance even in standard trim and many people buy them to finally get a fast and reliable touring scooter. Not everybody wants to fiddle with them. And most importantly – tuning a modern fuel-injected four-stroke requires a totally different level of know-how compared to the good old carb-fed two-strokes.
There are, however, a few indications that things are beginning to move here, and Gerald Fink, based near Graz in Austria, is a prime example. Gerald started his scootering career on a traditional smallframe Vespa that was soon heavily modified using a Zirri kit and the necessary complementing tuning goodies. After a few years, he moved on to a P200 and finally ended up with the GTS 300 after he decided he didn’t want any further spanner wielding! His good intentions held for exactly three weeks, then he found the standard GTS too boring to live with the way it was.
Whilst you can rely on decades of expert knowledge when tuning a traditional Vespa, Gerald soon got to the point where he had to make his own experiences or find people with the know-how he needed, even if they had nothing to do with Vespas. Whereas most people would have accepted that a certain tuning part or solution simply doesn’t exist, Gerald always moved forward, even if this meant he had to venture into unknown territory.
His starting point was fitting the 282 Malossi kit, including the complementing V4 cylinder head. Just by accident he spoke about his tuned Vespa to a reputable bike tuner, Otto Leirer from Simulations and Tuning Center (STC) Leirer, based in nearby Lockenhaus. Otto was interested in looking at the mapping of the scooter, plus he was able to provide a dyno to test the results. They found the Malossi-kitted GTS produced 22hp at the rear wheel, but was running dangerously weak (NB: a standard GTS 300 will show about 17-18hp on the dyno due to the losses in the transmission). They had a few attempts at setting it up, and finally ended up with a 1.5hp gain just by adjusting the software.
Gerald says that this was an eye-opener for him, as he learned that simply changing the hardware without adjusting the mapping to suit will not only achieve sub-ideal results, but is also likely to put the reliability of your engine at risk – you simply won’t know if it runs weak or operates in over-rev most of the time. Already by this stage a number of problems asked for solutions, the most important one being to find a way how to get a proper dyno reading throughout the whole rev-range. Gerald now uses a blocked pulley that will lock the scooter in a fixed transmission ratio comparable to a “third gear” on a normal geared Vespa.
Crash test dummy
By now all the tuning parts readily available on the market at the time had been used. But Gerald still found the results were not convincing enough. So he defined a new goal – he wanted to achieve 30bhp at the rear wheel, therefore nearly doubling the standard output of the GTS. Gerald says that this was the point when he really ventured into tuning, rather than just swapping parts.
In order to enhance inlet and exhaust timing, he started developing a tuned camshaft. At first the results on the dyno were rather unimpressive: Gerald found you can spend ages trying to get things right by working on a system of trial and error, as not only the height of the cam and therefore the valve lift has to be taken into account, but also the shape of the cam that determines the progression of the valve opening in terms of velocity and acceleration. To finally get reliable and comparable results, Gerald decided he needed a test rig into which the camshaft could be fitted, including a sensor that reads progression of the cams and overall height. Rather than spend tens of thousands of Euros on a professional set up, Gerald built the rig himself. Regarding the sensor and software side of things, it came in useful that Gerald works in a car crash test center – he simply used what they had readily available and re-programmed software that normally serves to analyse crash impact sensors. This setup provides a curve to visualise how the camshaft operates and therefore enabled him to monitor any required changes.
In conjunction with the camshaft, the aim of course was to provide the engine with more fuel-air mixture. The standard 32mm injection system was identified as the limiting factor for any further progress, so again some out-of the box thinking was required here. The solution came in the form of the 38mm MIU injection system taken from Piaggio’s Beverly 350. This is no straight swap, of course, as the harness needs altering and there is no suitable inlet manifold. Consequently Gerald has produced both a sand-cast and a CNC-machined version of a manifold, both items of absolute beauty in themselves. The whole system now breathes through a large K&N filter that sits under the left-hand panel.
Finally, the exhaust side of things needed attention. Having already said that the sports exhausts available for the Vespa usually don’t do much to improve performance on a standard bike, Gerald found them to be restrictive from a certain tuning stage, which is why he now uses an Akrapovic exhaust originally made for a superbike. Together with the modified inlet system, it provides the scooter with a deep, menacing growl at tick-over, that changes into an aggressive barking when you twist the throttle. Just from the sound you immediately notice the transformation the Vespa engine has undergone – this is a completely different sort of beast. If you have ever felt the hair on your forearms rise when revving a powerful machine, you can relate to the sensation. Brilliant!
Power-Torque Comparison: Graph (above) with power to torque comparison of different tuning stages (in this case readings with the CVT in operation, i.e. road setup).
- Black: Standard Vespa GTS 300, 17hp peak at the rear wheel
- Green: Vespa GTS 300 fitted with Malossi 282 Kit plus V4 cylinder head
- Blue: as above plus tuned camshaft and valve springs
- Red: as above plus 38mm MIU injection system and K&N filter
Looking at the dyno-curves, the flat shape of the power curve of Gerald’s GTS will tell you how well it has been set up and explains why the scooter simply pulls like a train whenever you twist the throttle. Gerald says that his main focus when building the scoot was for a smooth delivery of power. He actually could have reached his 30hp goal at the expense of some rideability, however he wanted a scooter that rides and handles just like a normal Vespa, only better in every respect. So even if the 30hp target hasn’t been achieved so far, I’d say this mission has definitely been accomplished. Even if it’s peak of 27.11 hp at the rear wheel doesn’t sound too impressive at first, the view starts to change when you realise the scooter still makes nearly 25hp at 130kph, where the standard bike has eventually run out of steam completely.
Fuel my fire
Gerald seemed totally relaxed about me taking the scooter for a ride, even if he warned me to take things slowly. I followed his advise and was rather careful about applying the throttle, which resulted in me being rather unimpressed by the performance at first – it all felt completely natural and just as standard. However, it eventually dawned on me that this was only due to the fact that the scooter was simply set up perfectly. The point came when I finally wanted to know what it’s really like when you grab a fistful of throttle – the front end suddenly went skywards with me desperately clinging on to the handlebars as the Vespa shot forward like a ground-to-air-missile underneath me.
I have ridden several automatic scooters, including some 500cc machines, but I openly admit that nothing prepared me for the absolutely amazing delivery of power from Gerald’s GTS. This takes four stroke tuning and lunacy to another level, one the market is crying out for. Hundreds of Vespa GTS owners would relish the chance of owning and riding something with a set up like this.
So what do we learn from this? Probably that where there’s a will, there’s a way. Gerald’s GTS is a perfect example of what you can achieve with dedication and a bit of ingenuity and I have rarely met someone so determined to move the goalposts of technology.
This is how two-stroke scooter tuning came to life and it’s great to see it spreading into the area of four stroke automatics. Saying that, there are so many things I haven’t mentioned, like the collection of about 20 different timing chain sprockets with slightly altered timing Gerald has tried out, just to test which works best, the Samarin superbike con-rod he now uses to enhance reliability of the crank or the Acewell multi-function instrument panel he has adapted for the scooter, including fabricating his own instrument facia to suit. Overall, his scooter stands out due to its absolute factory-like build-quality – there is absolutely nothing that has been bodged together – it all displays an unbelievable attention to detail. And that’s why I’m sure Gerald will not rest before his self-imposed 30bhp target has fallen – and I very much doubt he will afterwards.