whats the difference between red and blue 253

[Calum]

QR prefix would be high comp. Low comp got QS prefix during the years relevant to Sandman production. Holden achieved the different compression by the shape of top of pistons.

Blue 253 will have the prefix WR or VR.

Thanks men 'just for the back of the mind thing' but if its really only piston shape that makes the difference an old rebuilt engine still could be any thing !!