[RogerKnogeTopic starterBerichten: 4]

It’s an old timer cylinder with a new timer 10mm crank.
Dr50 piston, speed engine case portmatched to this cylinder.
Will use a 13mm carb and a gianelli fire (or power, havent decided yet)

I’ll start with a 64 jet and go from there.

Do you know if there is any “real” 38.4 heads with centered sparkplug? All i can find is theese stupid polini heads wich states that they fit 38.4 cylinders even though they are 43mm wide..

[RogerKnogeTopic starterBerichten: 4]

Thank you for the replies!

I decided not to grind extra ports for the transfers.
This is how it turned out in the end. Hopefully it will rip but I have my doubts 😕

[RogerKnogeTopic starterBerichten: 4]

• zevenenergie wrote:

  Hi welcome on the forum RodgerKnoger. Those holes should match holes in the piston. Your piston probably doesn’t have those holes and isn’t designed to have them. You’d weaken the piston. The theory behind those holes is that the pressure in the piston is higher than in the crankcase. That,s because when the piston moves down, the mixture is compressed by mass inertia.

  Thank you!
  I’m aware of the technical things to a point but at the moment the cylinder does not have those ports and I was wondering if I do gain any performance from milling out ports there (and also the piston). Does the cylinder need more air/fuel mixture than the ports already can provide.

  Or do I just lose crankcase compression and it will be a dead horse untill 9k rpm

[Gebruiker]

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