10 replies to this topic

[JackF]

I was looking at getting my 998 bored to +60 thou.
But I have read that a 998 can only be safely bored to +40thou.

Can anyone shed some light on this for me?
I have limited knowledge, so please bare with me.


Many thanks, Jack

[lrostoke]

http://www.theminifo...ig-is-my-engine

plus 60 should be fine, sure I've even read of very rare plus 120 thou

[JackF]

http://www.theminifo...ig-is-my-engine

plus 60 should be fine, sure I've even read of very rare plus 120 thou

Ahhh many thanks! A very usefull table!

[Tupers]

Mini Sport in Australia sell +120 thou pistons and Calver ST in the UK do +100 thou pistons. I can't for the life of me remember what either of those take the bore out to though.

[lrostoke]

will looking at that chart you gain 16cc for every 20 thou

So i'd guess 1078 and 1094 ???

[JackF]

conclusion; Its perfectly safe to have my 998 bored to +60thou?
regards

[Guess-Works.com]

It's not uncommon for IMP pistons to be used in a 998 engine, which as standard are 2.675", and also come in +20 and +40 making a bore of 2.715" which is a total overbore of +0.172"

ps. that chart needs updating to reflect the above...


 engine_sizes.pdf   10.29K   165 downloads

Edited by Guess-Works.com, 07 January 2013 - 03:59 PM.

[Cooperman]

I've used +0.080" overbore in a 998 which gives 1060 cc and that is fine.

[unburntfuelinthemorning]

I've used +0.080" overbore in a 998 which gives 1060 cc and that is fine.

Were you able to use the standard head gasket?

[Cooperman]

Yes, it was just OK, but I suspect that a bigger bore would have needed a different gasket.

 

As someone mentioned, I do recall Imp pistons being used together with a 1098 crank to get a real 'torque-master' engine. A fairly mild cam used to be used, such as the old BMC Special Tuning 731 rally cam, but these days something like an Evo001 would be great.

I do have a spare 998 block and a 998 crank. Maybe one day I'll build something quite radical. I think a 12G940 head and pocketed block would be necessary to get enough mixture in and out.

[unburntfuelinthemorning]

Thanks, that's useful to know.

 

If you're going radical with your 998 how about an 8 port head?  Or 16v one? 

 

Whatever happened to the overhead camshaft Howley 8 port head?  I always liked the look of that one.