4 replies to this topic

[luke6040]

Hey,

Im building a fast 998 engine with a 12g295 head and i was just wondering how much i would need to skim off the head and deak to get a good compression ratio, both head and deck have never been skimmed.

Thanks
Luke Lumley

[Guess-Works.com]

You need to work out the current compression ratio using the volume of the chambers, piston crown to deck, piston dish, head gasket and the crownto top ring volume around the piston.

Then using that information + the swept volume of the piston to get current compression..

from there you can determine how much needs to be removed volume wise to get the desired compression...

then it's a matter of determining how much of a skim on the head is needed to provide that volume reduction in the chambers.. for which you will need to find out the area of the chamber at the head face, and hope it does not change much.

[luke6040]

You need to work out the current compression ratio using the volume of the chambers, piston crown to deck, piston dish, head gasket and the crownto top ring volume around the piston.

Then using that information + the swept volume of the piston to get current compression..

from there you can determine how much needs to be removed volume wise to get the desired compression...

then it's a matter of determining how much of a skim on the head is needed to provide that volume reduction in the chambers.. for which you will need to find out the area of the chamber at the head face, and hope it does not change much.

Well if i say everything is standard 998 but +40 flat top pistons and standard 12g295 head, would anyone have a rough idea, just so i can make sure the workshop i take it to arn't just making up numbers.

[miniman1969]

I used this head years ago and had 80thou taken off to bring the CR to about 10:1

[luke6040]

I used this head years ago and had 80thou taken off to bring the CR to about 10:1

Cool ta so if they say somthing close i know ther not just making it up lol