Yet another soon-to-be-released ‘swap-in’ engine launched at the Scooter Centre show, but this time for Vespa Smallframes…
How times change. I remember well the days when 135cc was the upper limit of smallframe Vespa road tuning. Very soon you’ll be able to buy a self-assembly 250cc engine over the counter.
Smallframe engines of this size are not new, but those previously offered are all bespoke specials built using modified Quattrini and Fabbri casings by extreme tuners such as Egig.
This 251 however is a very different prospect to the balls-out 250 and 300cc specials, as it’s built using a previously-available kit cylinder from the Pinasco range.
In October it will be one year since Iggy’s Pinasco 251 hit the road, we’ll be bringing you an update during autumn
We’ve covered the Pinasco 251 for Vespa largeframe in great detail here at SLUK. It is actually a maxed-out engine based on the Vespa T5 layout rather than the PX or PX200. Both Iggy and I have bought and run them. For an over-the-counter engine with a box exhaust it runs well, producing around 24.5hp peak on our dyno with good torque at low rpm and fuel economy. I’d call the 251 a touring engine rather than a race motor, but Pinasco have other ideas and plan to modify one to use in their endurance racing smallframe, after finding great results in their initial track testing.
Small is Beautiful
What this new engine represents is a transfer of all of the knowledge and some of the parts from the largeframe 251 project to a brand new smallframe casing. The same 73mm bore ‘super T5’ cylinder kit and head is used, with a main exhaust port and 2 sub-ports. The wider-than-standard crankshaft is 60mm stroke and bell-shaped to provide enough crankcase volume for the 251cc cylinder. The casing also incorporates an 8-petal double-apex crankcase reedvalve with an S-shaped inlet manifold to locate the carb inside the frame.
According to Vittorio Zitun from Pinasco, the tuned version of this engine that they’ve secretly been testing for racing makes around 40hp, but this is with increased exhaust port timing and operating at higher engine rpm than the production kit.
Vittorio’s thinking is that it’s possible for a smallframe engine to make too much torque for a lightweight chassis; causing wheelies and trying to spin the rear wheel while cornering. This is also a reason why many other tuners put the power of their smallframe engines higher up the rev range. Raising the operating rpm means you can have massive power but at higher revs the torque figures are not ridiculous.
Obviously, the other technical improvements that the Vespa V-series has over the largeframe also continue into the Pinasco engine. The clutch is not on the end of the crankshaft for a start.
Note the screw on inlet manifold adapters for fitting different sizes of carb
What’s it for?
While Pinasco may be keen to prove this engine’s race credentials, if the smallframe version is anything like the largeframe then this should make for a good touring engine with surprisingly decent fuel economy. Note that people who tour and rally on smallframes do actually exist, even if they are a rarity in Britain. For those looking for a ‘sensible’ 250 smallframe engine Pinasco have already prototyped a downpipe to fit the traditional ‘banana’ type exhaust (e.g. Proma) but I severely doubt that will liberate all the potential power from this kit. Alternatively, with the correct expansion chamber then this will be a motor for those who insist on having the maximum over-the-counter engine capacity above all else. I’m sure that there are lower capacity smallframe engines that will make more power, but if you really want to rebadge your ‘50 Special’ as a ‘250 Special’ then this may well be a the cheapest and easiest way to do it.
The rear shock top mount has been altered to clear the exhaust downpipe on this scooter
Hang-ups?
While Pinasco make almost all the other parts that you need to build a quick smallframe engine (clutch, ignition etc) there are still specific pieces of the jigsaw that haven’t yet been shown, such as a specific head cowling.
Another issue is that the Pinasco engine is 1cm wider than standard in the direction of the flywheel (just like the Quattrini casing); which means that fitting a sidepanel door may be a challenge. The centre-plug head fitting also requires the kind of dexterity that anyone who has had to rejet a Vespa smallframe carburettor already possesses.
Finally with the position of the exhaust port gasket face there is less room for a 90-degree exhaust bend before it touches the shock. One solution – as shown on the demo scooter – is to fit an adaptor bracket to move the top shock mount towards the rear of the scooter.
Wide gasket face and alternative stud holes make this casing adaptable to some TM cylinders
Turbo-nutter option
Those of you looking carefully at the demonstration engine might have spotted a second set of cylinder stud holes. Apparently these casings are also adaptable to fitting water-cooled kart cylinders from TM. So far this option has not been tested, and may well require a dedicated crankshaft, but it’s great to know that they’ve thought about it as an option and made preparations for it. When and how much? The promised ‘when’ is early 2023. When the 251 Smallframe kit does arrive it is likely to be offered as a combination of casing, crankshaft and cylinder kit, to which you may add other Pinasco parts or those from a different manufacturer if you prefer. As for the cost; that again is as yet undecided but as a guide the largeframe version casing, crank, inlet, clutch and cylinder kit costs around €2,500 so it’s not unreasonable to expect this to be in the same ball-park for the same number of components.
Words and images: Sticky
Wow!
Best start saving then for my wee primmy