Yep, looks very similar to what I installed in 2006, which was suppose to be 9:1.
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OK found pic of TWR XJS racing piston , 11.5-1 ratio. i think the camera make top look convex/round , but i believe they are flat across the top!
made bt Cosworth UK.
Pete i dont think we will be using pistons anyway. LOL:roll_eyes:
i believe the piston does NOT reach the top of liners,(factory PreHE), its down .150 thou. down at TDC. 3.5MM. no squish at all!
ron
Are all 12 the same, or are the valve recesses a bit smaller on the exhaust side than on the intake side? That would mean six pistons with the bigger recess on the left and six with the bigger recess on the right.
also notice the bowl is NOT in center, its directly under the spark plug! TWR/&maybe Grp 44 pistons.
all the other factory type piston combustion bowl is centered, plus the odd changes in the squish area is offset!
most likly trying direct combustion direction plus add some swirl. Damifino.
ron
Nice picture Ron.
I was recently trying to see if I could design a piston to use with LS1 Titanium rods, and it ended up looking almost exactly like the Cosworth one (except without the little bowl in the middle).
Now I shall have to go back and see if I missed a trick there.
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Mark here is a drawing of a piston design, it has valve reliefs that would induce swirl and squish, both are necssary for effective combustion!
designed around 30years ago, in Daytona BCH Fla.
i little more for you to think about !
Good ole Smokey Yunick, Best Damn Garage in Daytona!
Bob
889076
Plymouth, Mi
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IrâŚthey could used a measured amount of light oil, to measure the volume of the bowl?
Against a known volume of each CR?
Call me crazy.
One of the things that entertains me is how much hand wringing and writing is done by Jaguaristas over easily answered questions. First let me say that since few vintage jaguars are driven with an angry wheel to the pavement it really doesnât matter if you have 7.8:1 or 9:1 other than bench racing. Virtually all piston manufacturers know what compression ratio their piston will provide in the original application - just ask them!
If you want exact results then simply bring your parts to your nearest precision engine builder and they will measure the actual combustion chamber ccâs, the thickness and sealing ring diameter of the head gasket, the piston deck height, and the piston. Then plug all that data into a calculation to give an exact compression ratio. And if you really want to have fun with math, you can calculate the dynamic compression ratio which brings into account how any given camshaft profile bleeds off or holds pressure in a moving cylinder.
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just jam the compression up, and damn the torpedoes!!
i like all the comp. i can get ,and then tune the engine to the fuel available.
I pulled an engine apart once that someone had built with Cosworth pistons.
Trouble was, theyâd put two of them in the wrong way around! 2A and 5A were incorrectly fitted! Luckily no damage done as the oil pump was so knackered they hadnât revved it so no harm done!