C90 High compression cylinder and piston kit 12V CDI engines

C90 High compression cylinder and piston kit 12V CDI engines
  • Click to enlarge

£86.80 £72.33 ExVAT

Product Code: 5717

C90 race cylinder and piston kit 12V CDI engines

1 x Custom high comp piston kit with rings, pin and clips NOW WITH EXTRA VALVE CUT OUTS

1 x 47mm Cast iron stock cylinder graded to match piston.

1 x Top end gasket set 1.1mm composite head gasket

We have now modified these pistons to work directly with the stock 90 heads and E22 heads saves on the hassle with incorrect cam chain tension.

Piston to valve clearance we haven’t got to alter the pockets for the stock C90 and E22 heads so all good there for stock cams worth checking if you’re using over 7mm lifts.
At the moment piston to valve clearance at 12 degrees before and after is 4mm so safe; you can run them as close as 2mm but no less.
Closet point to the head .70mm using stock 1mm gaskets any less you are at risk with piston to head contact resulting in the top lan failing.

Sadly price is high as these have been air freighted from Japan and we have had to invest in setting up to machine them all.

This is the very last standard pistons we could get..


This piston don’t just expect to put it in and ride it, as it almost 11 to one compression ratio you have no room for error with ignition or fuelling, before you will end up melting the crown or sizing up.

List of don’ts

1 Don’t use stock C90 CDI units you need one that will advance and retard verses revs.

2 Don’t use a CR7HSA only use a C7HSA unless you’re running D/C ignition.

3 Don’t just copy your mates jetting as there are a number of different cabs and needles that look the same, also main jet numbers don’t always mean the same thing. Some are flow rate some are in MM and some are just unknown!

4 Make sure you get it dyno set up, best results around 11 to 12% AFR one acceleration and no weaker that 13% flat out.

5 We recommend for endurance you run and oil cooler as they will start to burn the oil when it’s getting to hot.

6 Valve timing, if you want the best possible performance then set the LCA equal, inlet and exhaust.

7 Run 2 paper base gaskets


We have set up and dynode 11 bikes with this set up non of them have failed only the ones without oil coolers have lost their oil.

Worth running 20/50 if the ambient tamp is over 20c

Product Code5717