@louis Yeah the porting was the only thing I let a professional do.

Uhm no, I don't have that deep pockets.

Each component was done separetly. The final piece of the puzzle has been the underslung exhaust in an attempt to maximise the ponies out of the engine.

I ran the barrel stock on stock ignition for around a year.

However, the DTRE ignition, combined with the higher exhaust port actually had adverse effects.

So the engine in theory would have higher peak BHP, but because the CDI retarded ignition I was unable to utilise the gains.

So I then decided what I needed was an ignition system that would allow me to utilise the higher RPMs.

I didn't perform the porting work, but a professional did.

This is why I said, compression increased and squish altered so that the CC's are remained. Otherwise as you correctly said, you reduce the volume of combustable gases and thus reduce power.

You definitely sound like you know your stuff and you sound like a valuable asset to this forum!

The work on this engine has been an iterative development for around five years.

After everything I have done, it's still no better than a stock Rotax 122 engine. As such I have decided to end the tuning on the DTR engine and begin looking at building a Rotax weapon.