9 replies to this topic

[Sammy D]

I have an old 998 head here doing not a lot. My plan was to port and pollish it myself and fit it to my 1098. Brilliant, but what else can I do to it? Was thinking of getting some nice new different ratio rockers, but what else?

Sam

[Big_Adam]

VIZARD BOOK!

Also with the rockers much over 1.3 for a little engine is too much. 1.5 rockers take away rather than add. Righ whaty else could you do. Well theres the vizard mods like using rim flow valves and skilling down the valve stems so they don't block as much flow.

...hmm.....double valve springs perhpas (don't know much about them, so read up on them, might be a bad idea to use them) and thats about as much as I can think of. Again the vizard book will help greatly.

[Retro_10s]

Adam you've been doing lots of reading aint ya!

anyay, as above, higher flowing valves with differnt seat angles will increase performance.. mainly torque i think, and yeah skimming down the valve stems, though you have to be careful doing this as the valves take a hell of a beating in their lifetime.

rimflow valves are great but expensive. You could also upgrade to larger size valves... though you might have to pocket the block if you do this, or sink the exhasut valves in if i remember correctly. About 40thou?

getting a good manifold on your head makes big differnce too compared to a boggo one.

**hang on a sec, why are you gonna fit a 998 head to the 1098?.... the 1098 head is great,.. and the same as the 997 cooper head! (or was it 998 cooper?) if you're gonna fit another head to the 1098 make it a 1275 head!

Edited by Retro_10s, 12 December 2006 - 02:51 PM.

[Sammy D]

True true. What would I have to do to make it fit?

I just had the 998 one hanging around thats all.

[Big_Adam]

a 1275 head need the block pocketing, this is were you either have machined or gind out a section of the block to allow for the larger valves of the bigger head.

@retro....yes, yes I have. Well got to read something on the toilet.

[minivanman]

I think the 1098 head is a 12G295 - which is also the 998 cooper head. Very good head, I've got one for my 998. Its up at morspeed at the moment, getting "sorted". You'd be much better to modify this one than the standard 998 head.

[Mini-Dave]

wouldnt bother with the polishing as long as its ported properly!

Dave

[Big_Adam]

oh, also changing the combustion chamber shape helps.

[Retro_10s]

12G295 heads get rarer everyday!.... great head.

[fikus01]

get rarer every day!! does tha mean they are worth something?? i have 2!! both big valve units, 1 race and a john cooper garages conversion head that they fitted in the early 90's stil with the original twin carbs that has been blueprinted!!