S2 with TS head, max compression on 91 octane for street?

[Richard48Y]

I've been conversing with Salv Sacco about my TS engine build.
The readily available pistons are 78mm and listed at 11.7-1 compression.
Salv says they usually come in at 11-1. Seems a fairly big discrepancy.
I did CC my head today and it seems to have stock of very near to it chamber volume.
Salv says "The engine can handle that sort of CR as the combustion chamber is a very good design".
Not sure what the UK octane would be vs USA?
Prefer not to have to run booster as most is ineffective and all of it is expensive.
Also the risk of running out of boosted fuel as I do intend to put miles on my car.
I can buy race gas if I must, but if I have to do that, I will also have to put in a second fuel tank.

Thoughts?

[TurboFource]

Programmable water/methanol injection

[Pfreen]

That is a difficult question.  The camshaft makes a huge difference since it determines the effective compression ratio.  A late intake valve closing redices the compression ratio.
Also, retarded ignition timing will mitigate the onset of detonation.
Sometimes, different thicknesses of head gasket are available that can significantly change the compression ratio.  I don't know your engine, but for the twin cam, there are many different thicknesses available, so you can fine tune your cr.  Cometic is head gasket manufacturer that has many different thicknesses of head gasket for the tc.  I don't know if they make a Renault head gasket though.
Others on this forum probably could chime in on their experiences.
Btw, 98 RON Britain is approximately 93 Pump in the USA.

[Clifton]

I would find out what the UK uses for octane and ask Salv what timing runs at WOT. That seems like a lot of compression for an old style engine with out pentroof chambers.  As Pfreen said you can run less timing.

[jbcollier]

I happily run high-ish compression on mine with 94 octane fuel.  It's not as happy on 91.  The heads have a big "squish" area which creates a good deal of helpful turbulence.

[SwiftDB4]

For years I had a true 807G engine in an S1. Compression was 11.7-1. Had to use octane booster and even then broke rings a couple of times. Depending on where I lived I couldn't usually get gas above 91 octane.

[Richard48Y]

For years I had a true 807G engine in an S1. Compression was 11.7-1. Had to use octane booster and even then broke rings a couple of times. Depending on where I lived I couldn't usually get gas above 91 octane.

Sounds very much like a hot-rod Fiat 850 Spyder I once had.
I used to run AV-Gas in it.

Trying to decide, Wossner or custom JE pistons.
Wossner are less expensive but JE lets me have any compression ratio I desire.
Wossner can be cut down somewhat at the dome to reduce compression.
In either case I have to find a machine shop to handle boring my cylinders.

I am going to try to measure my current pistons for dome height.
Trying to clear space so that I may pull the engine and get a look at the cam.