Compression ratio (cr)

I could probably raise the cr by 1.5 to 1 by replacing the cylinder base gasket with a paper one. the base gasket is about 1.5 mm and I'm assuming 1mm gives a 1.0 ratio increase. This would take it from 9.5:1 to 11:1,

If I recall, increased cr increases power, but not by much, about 3% per 1 ratio. So about 1.5 hp increase. So maybe get 35.5 HP. But how will it affect torque!

I may get a little more fuel ecconomy, as the extra compression aids combustion. But as I get closer to knock limits, I will need to consider a higher octane fuel, so is it worth it?

Also, I obviously need to consider if there is sufficient clearance between piston and valves.

And then ... there are turbo's, that require a lower cr base value.

Some progress with the 2nd crankcase half.

I cleaned up the barrel sleeve with some wire wool. Still snug, but does go all the way in now.

When I had Visa -engine with GS -gearbox on my Dyane, I left those gaskets out. That because the other gasket was cut and couldn't find new ones, so I just measured, examined, tried etc, and after that, used some sealant instead of gaskets...

There was enough space for valves, liked the torque what increased so there was enough power to cope with longest geader GS -box. Also had Aisan -carburator (from 1300cc toyota), free flow exhaust, and with that I was able to have more top speed than needed. Calculated from rev counter, 7500 RPM, speed was about 173 km/h. Little scary, but not too scary at young age... Then I sold that engine-box to friend, who had it on his 2CV, hardly get 160km/h on 2CV body. The engine is still at good working order, but thowner hadn't keep the 2CV alive for years. I think I must call him, about selling the engine-box back...

Thank you @Jasu

That's very interesting. I guess if the barrel height is the same for 2CV and visa, then I'm ok. Don't have both here at the moment.

I may have been wrong about the visa cr. I said 9.5:1. But it could be 9:1.

looks like the visa barrel + the base gasket, is the same height as a 2cv barrel.

They had both. The CR should read at piston head...

Thanks, I will clean the crown up, and see what I can find. The engine numbers may give me a clue.

Research suggests, the stroke is the same for both engines @ 70mm

@jasu

The lower gasket you removed sits in an indent in the crankcase. Did you remove the lip from the crankcases so the barrels could sit flush, or did you just pack the gap with sealant?

I checked again, and the gasket doesn't sit in the recess! Which is odd, so best leave the lip there.

Piston looks to be 9:1 cr

Yay, got the crank back today. Not had time to play with it yet, but confidence is high