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Tune an air-cooled Scomadi 125 to be as fast as a 200, or a Vespa GTS 300? That’s what Readspeed said they could do so we offered them a SLUKing challenge to prove it.

 

This is the challenge that some of Readspeed’s vocal critics claimed was impossible. Well let’s see about that shall we?

 

4-valve head conversion massively improves gas flow.
4-valve head conversion massively improves gas flow.

 

What has changed?

 

If you remember back to the last article, Readspeed’s big-bore 170 conversion was put up against a Vespa GTS125; which it beat. This is not the one-sided competition that you’d imagine because even though the Scomadi engine had a greater capacity, here was a very basic Chinese 2-valve air-cooled motor that was tuned to beat a sorted 4-valve, water-cooled, fuel-injected 125.

 

This time the target was a lot higher. Jerome aimed to beat a Scomadi 200, which is a water-cooled 4-valve that’s pretty close on performance to a Vespa GTS300. How the hell could you do that with the same basic air-cooled Scomadi 125?

 

 

No replacement for displacement

 

To take performance to the next level required far more than simply fitting a bigger bore barrel, although with a 4-stroke that should always be the first step.

 

  • 60mm long-stroke crank (standard is 57.8mm)
  • 63mm bore cylinder kit (standard is 52.4mm)
  • 4-valve head
  • “Conservative on compression”
  • 28mm Keihin carburettor
  • Standard transmission – original belt – 10.5 gram rollers
  • Readspeed up-gear kit
  • Oil cooler
  • Scorpion Scomadi exhaust (baffle removed to reduce heat build-up)

 

Air-cooled and proud
Air-cooled and proud
Watercooled and stage 3
Watercooled and stage 3

 

Scomadi 200 on hand

 

In order to compare we needed a Scomadi 200 to try and Readspeed customer Alan was good enough to bring his FP200 along. If you can remember back that far, FP stands for First Production. This came with a few extras as a way of saying thanks to those who supported the project by crowd-funding. Alan’s scooter has a PM Tuning EFI box, exhaust and variator so it’s effectively a ‘Stage 3’ and probably a little faster than a stock 200.

 

Alan’s had many scooters and also rides a Vespa GTV so he would be a perfect judge for how well Readspeed had done tuning their much-abused 125.

 

Adding to the mix was Phil from Readspeed, riding the shop demo 2017 Vespa GTS 300.

 

VIDEO: 3 way battle

 

Who won?

 

Well, as you can see from the video, it was closer than the fondness of a priest for his favourite choirboy. Top speeds for all three were broadly equal with the only unifying factor being that the Readspeed Scomadi 190 always stole a few yards due to quicker initial acceleration. After that, slipstreaming came into play so we had various outcomes depending on who was crafty and who was aerodynamic.

 

Given that we don’t have a lot of faith in speedometers we GPS tested the 190 and Phil got 76.4 mph out of it on the same short stretch of dual carriageway. Given a longer stretch it could probably be coaxed to go a little faster. Certainly it’s massively faster than a standard 125 or even one of Readspeed’s 170 conversions.

 

Big Keihin nestles under the plastic fuel tank
Big Keihin nestles under the plastic fuel tank

 

What does this mean?

 

Well, it means that Jerome can rest easy. He’s done enough to prove that they can make a Scomadi 125 go better than a Scomadi 200 and there’s still more power to be found from that engine as well in the form of higher compression if it was needed.

 

The plan was always to keep this motor reliable so it can act as a shop demo for their air-cooled 4-stroke engine tunes.

 

Naturally there are limitations, as Phil explains: “this is not a full-throttle motorway engine – it’s air-cooled so it needs to be treated with respect. The oil-cooler is a necessity.”

 

The oil cooler is a necessity
The oil cooler is a necessity

 

Want to buy a 190?

 

Readspeed haven’t given us the full price of building an engine like this because they aren’t expecting many people to want one. The cost is likely to be significant; probably more than the difference between buying a Scomadi 125 and the 200 version. However, if you really wanted a fast 125 for some reason, you could give them a bell.

 

For those of you wanting a more affordable power-up for a Scomadi 125 (or the Peugeot Django for that matter) then Readspeed have a far cheaper and more practical 170cc option available as well as upgear kits to suit. You can buy the 170 kit direct from Readspeed here.

 

 

Sticky

 

Thanks to Phil and Alan for help with the test.

 

 

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