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Looking at some new old stock Karl Schmidt pistons for my Shorrocks blown fast road mini engine, they are 4 ring, solid skirt type - presumably they are cast replacement pistons? Are they good quality and would they be suitable? Or would I be a lot better to dig deep for some forged Omega ones or is that just over kill bearing in mind occasional 6500 rpm with low CR and max 7 psi boost?

Thanks for any opinions, regards Paul.

I run them in my 1293 - there the only thing that survived the last engine blow up (along with the rods)

And occasionally a lot of the time there spinning @ 7-75k . Id quite happily use them , probably not the lightest thing on the planet.

Pad

I've had some D-top Karl Schmidt pistons in my 998 Cooper for the last 20 odd years and 20k on I haven't had any problems.

put a set of plus 60s in my 850 ! dam hard to find , they were forged and really nice quality, not done many miles yet, but cant see why there would be any issue at all

Thanks everyone for your comments - sounds like they are good pistons. Unfortunately I'm now having to go down the custom piston route (probably JE Pistons) as my Speedwell head has been successfully repaired and to get the require compression for the Shorrocks supercharger on a 1098 means about a 12cc dish in each piston.

Paul.

Swiftune and MED sell forged omega pistons for 1098 engines

Thanks Simon and yes I've already considered both of these options but both can only take 6cc dish max, nowhere near the 12cc I require because of the head and the blower.

Cheers Paul.

What CR & boost are you aiming for. Either your Speedwell head must be very small or you are aiming for a lot more boost than is advisable.

M.

Hi Mark,

My Speedwell head has chamber volumes of 23.3 cc and I'm aiming for 7psi boost on a 1098 with +20 overbore at a compression ratio of 8.5:1, in my calcs I have allowed for 2.8 cc in the head gasket (figure from Mini Spares web pages) but 0 volume allowance for block deck height (assuming the pistons will be flush with top of block) and also 0 volume for land height above top ring (not looked into calc for this).

Am I way out with this or about right? and is 8.5:1 a good compression ratio to aim for to avoid pinking on normal unleaded petrol in UK?

Cheers Paul.

7psi of boost on 8.5CR would no problem at all as long as everything is correctly set up.