Javelin new pistons

[PaulRM]

Hi all

I have recently purchased running donor engine (E3 PE 24559) that I intend to rebuild to Jupiter spec for my Javelin, using higher compression pistons. A friend, upon hearing about this endeavour, suddenly produced a box of new pistons he had once intended to fit to his Jupiter engine rebuild but never did, owing to his rebuilder (Dennis Sparrow) preferring to use his own.

The pistons in question are flat top, with a bevel cutout. I assumed they were competition items. However the compression height - measured from the centre of the gudgeon pin to the top of the piston is only 37mm, as opposed the standard 39.5mm. Perhaps these are examples of those made by the Jowett Car Club? I'm not sure. The piston are .5mm oversize, which corresponds to 2nd oversize in the Javelin Manual (I.e 20 thou)

Can anyone identify the provenance and suitability of these items?. Below are pictures of one of the pistons, including the maker's mark on the inside:

[David Kemp]

Look like Mazda to me.
Measure the gudgeon pin.
As mazda is different from Jowett.
The club sells the correct size little end bushs to adapt them.

[PaulRM]

Thanks David

What was the angled cut out for, originally? For valve clearance ( on a Mazda)?

Paul

[David Kemp]

I don't know why the cut out. I would guess like you that it is for valve clearance.
Club members here (OZ) like the Mazda piston as it is a lot lighter than the Jowett piston.
No one has found the cut out to have any effect on performance.