Well hell, the theory says you should have as close piston to head clearance as possible - to reduce knock tendencies, increase torque and bhp. Thing is though, the first race engine I ever self built had pistons 30 thou down the bore. It ran like a scalded cat and wasn’t fussy on ignition timing either. But I get the theory, so normally get the pistons as close to the deck as possible.
So how to get a decent turbo friendly cr, as well as a compact burn area (in the middle of the piston if possible)? Well I’d be looking at cutting the chamber walls back as much as possible, maybe cutting a corresponding slot across the piston top, and then minimising top clearance.
The idea of not having electronically mapped ignition and knock detection is daft - it will cost you power, or a melted piston. (Looking down a plug - hole and seeing the gudgeon pin is a bit of a let down).
So with mapped ignition and knock detection - and the right shape combustion chamber, you should be ok at 9.5 to 1, or even higher, maybe 10.5 to 1. The lower the static cr the lower off boost power you’ll have, which increases lag etc.
Do this, with mapped fuelling and 12 psi of boost to start with, let us know how it goes?
Oh, edit to add - forget about balancing this and that, and gaining the last 95cc - build the cheapest engine you have, it will be an experimental mule, so if it melts so what. Spend your money on essential machining, new rings, the mapped system and a good condition turbo (of the right size - this is as important as anything).
So how to get a decent turbo friendly cr, as well as a compact burn area (in the middle of the piston if possible)? Well I’d be looking at cutting the chamber walls back as much as possible, maybe cutting a corresponding slot across the piston top, and then minimising top clearance.
The idea of not having electronically mapped ignition and knock detection is daft - it will cost you power, or a melted piston. (Looking down a plug - hole and seeing the gudgeon pin is a bit of a let down).
So with mapped ignition and knock detection - and the right shape combustion chamber, you should be ok at 9.5 to 1, or even higher, maybe 10.5 to 1. The lower the static cr the lower off boost power you’ll have, which increases lag etc.
Do this, with mapped fuelling and 12 psi of boost to start with, let us know how it goes?
Oh, edit to add - forget about balancing this and that, and gaining the last 95cc - build the cheapest engine you have, it will be an experimental mule, so if it melts so what. Spend your money on essential machining, new rings, the mapped system and a good condition turbo (of the right size - this is as important as anything).