12 replies to this topic

[Stevelee10]

Hi. I have a stock 998 with a deep scratch in the cylinder. So since I have to get it rebored I thought I might as well geta bit more grunt from it so I was thinking of going +100 but I'm wondering if this would cause any problems
I.e. poor reliability. Does it require an off set bore etc

[cal844]

+100 would see you through the water/oil gallery imo

[pickuptruck1994]

i know someone who is currently fitting 100+ pistons to i think 1098

[Dan]

Lots of people have used +100 over the years, they seem to go in and out of favour based mainly on availability, and +120 has been achieved. I think the popular old Imp pistons basically worked out at being +100 too. Right now +100 are available from Keith Calver, but I would suggest trying his +80 first, or at least getting it ground for them even if you don't buy them. Or maybe even starting at +60. If that will get rid of the scratch then stick with it, if not grind again. At +100 the central web between 2 & 3 is very small and the head gasket highly stressed in that area. In my experience large bores in the small bore block are troublesome and give unreliable gasket sealing.

[Gr4h4m]

See what the machine shop say it needs to go to

[crazirob]

what would that put the displacement too ???

[Stevelee10]

I was just interested in how bigi could go and what it would achieve. As I've seen companies selling +120 for a 998

http://minisport.com...lat-top-hypatec

[liirge]

120 = 1096 I've got an engine, runs nicely, to be honest the torque increase you might expect isn't noticeable. You need to offset the bores on the 998, otherwise you'll be running into problems with the headgakset (if you're going to use a 1275 head and gasket.....would be silly not to, frankly).

Edited by liirge, 11 February 2015 - 04:56 PM.

[liirge]

Actually I think it's those pistons as well, they came with a good quality Hastings ring set.

Edited by liirge, 11 February 2015 - 04:59 PM.

[Cooperman]

For a 998 a +0.080" over-bore is very good. No need to offset the bores and flat top pistons are available. If doing this you won't seem much difference unless you also have a fully gas-flowed head with bigger valves and an improved cam, exhaust, dizzy and inlet.

Alternatively just bore to the next size up and enjoy the car for what it is - an old classic car.

[Spider]

Yes, an Off-set Bore is required. I think I still have a couple of sets of +100 for a 998.

[Stevelee10]

Thanks guys. Think I'll go +80 and get the head gas flowed with a better cam. This engines never been rebuilt and its a little tired. So could do with a bit of TLC so might as well go the whole hog and do the lot

[Gr4h4m]

Before spending your hard earned pennies on Pistons get it to the machine shop for them to size it up and advise what needs doing. Then order the Pistons so they can complete the Boeing work.

The calver Pistons have taken some abuse in May car and been great so far