got a 998 with a pipercross airfilter any good ideas to boost the performance?
Fit a 12G940 head, sink the exhaust valves by 40 thou - and an HIF 38 carb on alloy inlet manifold, with the best exhaust system you can afford. But - to get decent horsepower, you will also need to swap the cam. MG Metro is good!
can anyone recommend a decent exhaust system?
Maniflo always get good press.
your a pro, cheers man.
christmas shopping list now completed. haha
> Fit a 12G940 head, sink the exhaust valves by 40 thou - and an HIF 38 carb on alloy inlet manifold, with the best exhaust system you can afford. But - to get decent horsepower, you will also need to swap the cam. MG Metro is good!
What is needed to sink the exhaust valves?
Does a 12g940 head bolt onto a 998? I though the number of studs was different… or does it not matter?
the studs are the same unless someone has 11 studded it it does fit straight on if unskimmed from standard and if on standard cam but not advisable. sinking the valves is one way but also not nice they need to be recut with special tools ideally the block needs pocketing some companys will do this for you on a built up engine (ie head off)
i built a 998 to the following spec
1030 block (998cc +40’)
rebuilt 12g940 cylinder head
sw5-07 cam
lightened duplex gears
center main strap
rebuilt box
megajolt
maniflow stage2 lcb and single box system
hif44
makes for a nice engine, plenty of power mine hit 68bhp on our local rollers but i got a feeling they are reading about 5bhp over
whats bad with sinking the exhaust valves 40 thou?
no need for a main strap unless you will be running very high RPM which i doubt.
> whats bad with sinking the exhaust valves 40 thou?
the money outlay.
sinking the exhaust valves in effects flow and valve working angle. its not the nicest way around the problem
> no need for a main strap unless you will be running very high RPM which i doubt.
yep i agree but i had access to the machine shop so for the sake of a few quid i bought one and machined the top of the cap
any other heads which give decent performance and are reasonbaly priced?
12g202 or rare 12g206 if you can find one i use these as a starting point the 202 is from 1098 engines and has bigger valves than the 998 with bigger ports too. but i port and change the chamber shapes also bigger valves if i want but for cheap cost just use what ya got.
> 12g202 or rare 12g206 if you can find one i use these as a starting point the 202 is from 1098 engines and has bigger valves than the 998 with bigger ports too. but i port and change the chamber shapes also bigger valves if i want but for cheap cost just use what ya got.
are you sure the 202 has bigger valves? i have a standard head and a 202 side by side at the moment and they look identical. there is definately an increase in the port size though.
The obvious head to go for is the cooper 12g295 head, there is one in the classifieds at the moment, this spec’d engine does NOT require the 940 head. skim the 295 down to the Compression ratio you want and use that.
yeah 12g295 heads are good if you can get one that is ok for ok money usually £100-£150 and need calculating chamber volume and a large skim to lower it enough for the 998. Yeah im sure the 202 has larger inlet valves they are not huge but are bigger from 998 head 26.99mm to 29.36mm in the 202 head i have a few heads and can be picked up for as little as free lol seriously i paid £10 for one as everyone wants to fit big heads but sometimes they are too big
295 all the way!
