Forged Pistons

[wrx kenny]

as a few of you now know im going for a 2.5 block , what i keep seeing is forged pistons at 2 different sizes 99.5 and rebored 100mm whats the difference , whats the best option and what difference does it make . thanks in advanve for your answers.

kenny

[arch]

as a few of you now know im going for a 2.5 block , what i keep seeing is forged pistons at 2 different sizes 99.5 and rebored 100mm whats the difference , whats the best option and what difference does it make . thanks in advanve for your answers.

kenny

Depends on your current bore and whether it needs bored oversize or has been rebored.

[BalliSTIc]

as a few of you now know im going for a 2.5 block , what i keep seeing is forged pistons at 2 different sizes 99.5 and rebored 100mm whats the difference , whats the best option and what difference does it make . thanks in advanve for your answers.

kenny

Assuming you're using a 79mm crank, 100mm pistons put your cc up to 2484 (from 2457cc). 30cc is probably of questionable benefit. It will also mean SLIGHTLY heavier pistons (being bigger) which will add to the rotational mass - again a marginal increase - although forged pistons may well be lighter than stock anyway.

A larger bore will thin your cylinder walls which might lead to problems at MEGA high boost, but at more "sensible levels", 0.5mm is really neither here nor there.

I guess the issues are:

1 If you NEED a rebore due to cylinder damage/ big ring gap etc, and:

2 If you want more cc

If you just need a rebore, you'll need the slightly larger piston. If you're after a significant hike in displacement, 0.5mm is probably a waste of time.

If you're getting a new block, forged 99.5mm pistons will do you fine.

[colin_ross]

As above I'd stick with the standard size. Performance and reliabilty differences will be minimal but cost won't be when machining is taken into account.

[wrx kenny]

^^^^^^^^

thanks thats what i wanted to know ,its all clear now , every day is an education in the world of subaru

kennny