Recently, SLUK Racing took our second overall win at the BSEC 6-Hour endurance race. It’s the second one we’ve won outright, but the first using our new engine.
Do you want to know what’s inside and why we chose it?
It’s all about the ‘S’
A while back we ran this feature on Max Quattrini’s new method of cylinder kit design, using not only dedicated ‘flow’ software, but now also using a physical flow bench to test the actual gas flow of various 3D-printed port shapes. The result was astounding, with Max claiming up to 30% flow improvement, meaning increases in power over the whole rev range without changing the port timings. That’s quite unheard of in 2-stroke tuning.
The first kits to get this ‘S’ treatment were the M1L 60mm (144cc) reedvalve kit for smallframe Vespa, and the M200 kit for Quattrini’s own smallframe casings.
What we wanted
As with any race series, the scooters at British Scooter Endurance Club’s meetings are getting quicker and the teams are more professional at each event. Our old M1L 125cc race motor dates back to 2012 when it was fitted to my SS90 ‘Underdog’ and converted to road use using a 54mm stroke crank.
As a relatively long-in-the-tooth pilot I wanted more torque and fewer revs. This tune, and adding a Ludwig and Scherer ‘Franz’ exhaust, gave me just what I wanted; around 21hp with a wide spread of power but at moderate revs. Certainly it was quick and reliable enough to win the third BSEC endurance race we entered, but it too was long in the tooth, and we were getting left behind down the straights by Targa Twins, an M200 and several RBs.
We needed a little more power, but not difficult-to-access power. We wanted to maintain the same level of easy rideability and reliability, but just to add a few more ponies. As such the new ‘S’ version of the Quattrini M1L 60 seemed just the ticket. More power, but not too much power…
The case of the casings
Our old engine was like Trigger’s broom. The only constant was the Quattrini kit which is on its original plating but has had new pistons. It had so far consumed two Piaggio smallframe casings (one cracked around a weld and the other with spun main bearings. For BSEC’s first 8-hour race we tried SIP Scootershop’s beefed up smallframe casings and we were well in the lead of that race for 6 hours when the crankshaft shat itself in glorious style and turned into a milling machine. The SIP cases will live again, but not for this project
Thankfully, Max Quattrini (pictured above) had already managed to persuade us of the advantages of his new casings with the lure of a wider, beefier crankshaft and a casing made from quality aluminium that rings like a bell when you tap it with a screwdriver. Try the same with a Piaggio case and you get the dull thud of a production casting.
Quattrini casings offer numerous advantages for prospective smallframe engine builders:
- Better main bearings
- Beefier crank
- Gasketless assembly
- Clearance for 3.50-10 tyres
- Transfer port cutouts to match Quattrini’s own cylinders
S for Sexy
Unlike the M200 kit – which has a widely-spaced cylinder stud pattern to maximize port design, the M1L 60 S uses the Piaggio stud pattern. Essentially this kit would fit onto Piaggio casings but the Quattrini casing was simply better suited to the task.
While externally similar to the old M1L kit, the new ‘S’ is completely revised inside. Instead of a main exhaust with two small sub-ports, the ‘S’ kit has four sub-ports flowing either way around two of the cylinder studs. In terms of casting complexity, it’s quite a work of art.
Unlike many people who dabble in 2-stroke tuning, I don’t believe I know more than the people who designed a particular engine. Generally, if you build a kitted motor in the format that the engine builder intended then you should get the same good results that they did. Only once you’ve tested it in that specification should you think about whether, or how it may be improved to suit your particular demands.
I see so many people buying kits for Vespas and Lambrettas and fitting the longest stroke crankshafts that they can get in a bid to maximize engine capacity, without considering that this action may actually mess up the port timings and make the kit run worse. Long-stroking does work, but you normally need to adjust the port timings again afterwards to release its full potential.
All this is explained fairly thoroughly in my Lambretta Kit Book; which is also worth reading even if Vespa tuning is your bag.
Starting Spec
To begin with we gathered the following parts:
- Quattrini casing for standard studs: the latest ones are modified to accept the M1L 60 S kits and their specific exhaust routing
- Quattrini crankshaft with 51mm stroke
- Quattrini M1L 60 S kit and dedicated cast aluminium exhaust manifold
- Quattrini M3 150 S exhaust which is only for the S kit
From our old engine we’d use the following:
- SIP Vape ignition system. So far it’s been brilliantly reliable, though the fan is a little heavy for race use
- Quattrini M1L inlet manifold for 30mm carb. The one supplied with the kit is for 34mm carbs and that seemed excessive given the endurance racing advantage in having decent fuel economy
All we needed after that was a full transmission set-up and the best deal offered to us on that came from Crimaz who basically manufactured everything we needed to fill the casing.
The Quattrini casing comes with a plug and O-ring to fit if you aren’t going to run a water pump.
Stage 1: Quattrini Casing Prep
It’s a pleasure to work with brand-new casings. Aside from a little de-burring on things like the oil feeds to the main bearings the cases were ready to go. They come with the transfer openings pre-machined for Quattrini kits which makes life easier.
There’s also an extra O-ring in the casing where the gearshift rod goes through and smallframe motors are prone to leaking.
On the advice of Dave from Hornet Racing, I ground away some material (marked red) from the clutch cover gasket face to make it easier to get a range of clutch systems in and out. This is only doing what was already done in many Piaggio casings.
The Quattrini cases are not supplied with engine mounts so we fitted these BGM ones.
Following the train of thought that the scooter had always handled acceptably on rubber engine mounts so we chose simply to upgrade to BGM’s latest rubbers which have a soft and hard side which is colour-coded on the tubes. The thinking is that the harder rubber is used on the side that supports all the engine weight and the soft rubber on the other side offers a compromise on vibration transmission. As an endurance race motor that would be run for hours at a time it’s important that the riders and chassis aren’t shaken to bits. If that wasn’t enough stiffness then we could always fit another hard one on the left or upgrade further to polyurethane like those produced by PLC Corse.
So far so good.
Words and photos: Sticky
