Need for Speed

Stuart Gentry is about to put a mark on the scootering map with the introduction of his 261 cc P-range, a Vespa with the potential to hit the magical 100mph in real world conditions.

Nik and Dan take a look at the inner workings of SG Engineering, and owner Stuart’s passion to hit 100mph on his P-range Vespa.

30mph-90mph+ in top gear

Started only nine years ago by someone with no historic connection to the scooter scene, SG Engineering has become one of the best kept secrets of the industry, with their 230cc engine developing a reputation as one of the best touring lumps around. Owner Stuart Gentry gave Scootering an exclusive look at his new Vespa 261cc engine, with a hint of more to come; a machine that’s already been clocked via GPS at a pretty astounding 94mph. Sadly it started to suffer fuel starvation at that speed, meaning that he couldn’t ride it flat out for extended periods. So although he’s not managed it yet, the current performance is a good indicator that Stuart is going to hit that magical milestone sometime soon. An important thing to remember here is that the scooter isn’t a peaky rev-monster.

Stuart says that he designs engines to roll on from 30mph in top, pulling all the way to top speed, even with a pillion on board. While this may not make for a screaming quarter mile machine, it does allow for a very rideable scooter for day to day and distance work. A quick chat with the somewhat modest tuner behind these engines was definitely needed.

A word with the man

“I’ve no background in scooters, I come from an engineering background though, working as a development engineer in plastics until I was made redundant, designing castings and the like. I’ve never minded getting my hands dirty though, and used to help a mate who was into scooters keep his running. It just developed from there.

“Around 25 years ago I used to go watching motorbike racing, and would spend as much time as possible in the pit lane watching tuners doing their thing, and learning from what I saw.

“From there, I’d bring bits of knowledge home with me and apply it to scooters that I’d be playing with for friends. Setting up the carb properly is very important, it’s a major cause of so many problems, and something I learned to do. Even though I’ve now got a dyno, I tend to do my initial set-up by ear, and results on the rolling road show that I’m generally pretty close, and I’ve had scooters coming back to me after a few years, ones that I built before the dyno, that are still pretty much on the mark.

“It was a bit of a running joke that people would ask how a fast scooter I’d built would make it home from Weston-super-Mare in one piece instead of coming home on the back of the AA van!

“One day I was offered a P200 in part payment for some work I’d done; it seemed a reasonable deal so took it. This is the scooter I still ride now, a Mk1 P200, and it was the test bed for the 230 straight from the off. I’d had the engine spec drawn up for a while, but I’d never been in a position to build it, so it seemed like the ideal time to finally do it. I’ve always thought that ‘little is more’ when it comes to tuning engines though. 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.

“Scooters can be finicky, so the secret is to allow for the weak points while making them as powerful as possible. One thing I do, and it’s something that seems to have recently become popular, is to pressure test for leaks. It always seems to be the engines that you think can’t possibly have a leak that do!

Don’t get the idea that I’ve come up with any new ideas though, I haven’t. All I think I’ve done is to take old ideas and use them better than they have been historically

“The biggest difference in the way I like to build engines is with the way power is produced. Most tuners seem to build machines that scream up to top speed rapidly, giving a very narrow and peaky chart on the dyno. In comparison, mine have more of a diesel type power curve, one that’s very broad and flat, allowing for a low rev roll on to pull away, something I think makes for a much more relaxed riding. Bear in mind that you’re riding something with awful aerodynamics, so grunt is more important than outright revs in my opinion! Up-gear the engine and you’re away, as it will happily pull higher ratios due to the torque figures being in the region of 20lb-ft on the 230.

I had one of my customers from Skegness tell me that he’d been leaving TS1s behind going up hills to Scarborough. He was still in top when the Lambrettas had dropped to third or even second, so this suggests that I’m heading in the right direction for road scooters.

Don’t get the idea that I’ve come up with any new ideas though, I haven’t. All I think I’ve done is to take old ideas and use them better than they have been historically, but I wanted to do things that people have always said you can’t do to a Vespa. Although I’ll work on Lambrettas, the new generation of P-range casings and cylinders have largely levelled the playing field with them, but at a much reduced price, meaning that the 260 is a high speed mile muncher that can be built at a better price than the competition. Although it’s not hit 100mph yet, I’m convinced it will do, and if that fails… well, let’s just say that there is still more to come!”