15 replies to this topic

[087dave]

Hi all i have a project 998 with a stage 1 kit, stage 3 head, sw5 cam, ligthened flywheel, and flat top pistons and was thinking would i have lots of compression with the flat top or go with dished ones also would the head need skimming (i brought the head at minisport) with either of the pistons.

Thanks in advance

[Rosslin Racing]

have you worked out what compression you have?

[087dave]

No, do you mean a compression test?

[Rosslin Racing]

no if you have the head from Minisport you should know the CC of each chamber it may well be stamped on the head you then work out the volume above the piston, a bit of maths later and you have your compression, you dont want to go more than 11.1 on a road engine with normal petrol.

[mini93]

with dished pistons you get more swirl from the air entering the cylinders, this aids fuel air mixing and so are usualy better

[087dave]

Thanks how do you work out the volumn above the piston? if i have the cc off the head Thanks

[Ethel]

Thanks how do you work out the volumn above the piston? if i have the cc off the head Thanks

Have a search 'n google it's been covered many times. It will be cheaper and easier to alter the head volume than fit new pistons.

[087dave]

no if you have the head from Minisport you should know the CC of each chamber it may well be stamped on the head you then work out the volume above the piston, a bit of maths later and you have your compression, you dont want to go more than 11.1 on a road engine with normal petrol.

The numbers that i got of the head is cam4810, 1407 and also BIL is marked on the head

[Rosslin Racing]

they normal stamp it on top of the head around the outside of the rocker cover gasket line

[087dave]

No there is notting stamped on that part of the head, but should minisport have skimmed the head before i got the it?

[Ethel]

They should really have discussed compression ratios with you. Is there any info on their site?

If they worked the combustion chambers it would need skimming to restore the original volume.

[087dave]

Thanks what would you think is the right compression ratio from my engine

[087dave]

Do you mean cc of a head is that the size of the valves if so they are inlet 29mm exhaust 25.4mm THANKS

[Racer_Pete]

I doubt you will want dished pistons, flat tops will keep the c/r up which is all ways a good thing unless its really high then maybe you should consider dished pistons.
Maybe give MiniSport a call and they will tell you the size of the cc.

[Rosslin Racing]

you will have to litre the cambers with a plug in and valves that way you will know that you have a chamber size of between19cc and 25 cc

Edited by Rosslin Racing, 08 February 2009 - 06:01 PM.