Tuning the combustion space

[Keith Clements]

http://jowett.org/jowettnet/dt/tech/JAVELIN-TUNING.pdf
are the tuning notes with compression and combustion space figures for Jowett pistons. Anyone know what the difference was between those three piston types?

Bear in mind that that was for Javelin gasket; not the thinner Jupiter one.

I will have to dig out what I set the CC space for the Fiesta pistons; from memory I aimed for 9:1.

The calculated compression ratio is really only a guide to aim for in getting the most power or torque from an engine. The most important thing is to get all the spent gas out and as much cold petrol mixture back in. That is done with good gas flow which is a synergy of theory and experiments with inlet and exhausts tract honed to perfection and the combustion chamber and piston crown working together to swirl the gas in the direction required.

Anyone done any quantative testing on Jowett gas flow techniques?

[paul byrne]

Re the different pistons mentioned in the Tuning Notes, it could well be that the difference is simply the depth of the bowl. I say this because it seems that the 8 to 1 piston musthave been almost flat topped as the combustion chamber space including the gasket and any bowl is given as 52 to 54cc with these pistons while the combustion chamber volume in the head only is given as 40 to 41cc.
53 minus the 7.5 for the Gasket leaves about 45.5 cc which isn't far off the head-only volume ( the 5cc difference equates to a volume with the diameter of the bore and only 1.2 mm high, it wouldn't take much of a dish to equal that)
Cheers