When you talk about compression ratio of cylinder head 10.5 :1 is that 10.5 "BAR" to 1?""

 

Hi ralsy,
No it's PSI mate.
By the way have you seen my new Truck?
all the best
Spider

 

No. There are no units on a compression ratio because that number is a RATIO, so it's dimensionless, and it's a ratio of volume, not pressure. The volume of the space above the piston when it is at the far end of its travel is 10.5 times larger than the volume of the space above the piston when it is at the top of its travel and the spark plug fires.

 

Right. A volume of gas of 10.5 cubic units get compressed to a volume of 1 equal cubic unit.