850 turbo
yeah you can do it but doing it reliably is the thing. the 850 engine has alot of weak points in standard form and the avalibility of upgrade parts is very poor these days. you will have to collect parts
con rods - standard ones have clamp small end and can break replace them with 998 cooper ones/ 1098 cc A series ones.
Pistons - standard ones have slotted skirt and are very weak, choice or replacements is very limited i think it was heprolite made performence ones for it but iv never seen any, or you can use new 998 performence pistons which will give you 894cc, or you can fit sprite 948cc pistons but you will need to skim block to get compression right but this could be useful in getting compression right in a turbo 850.
crank - you want the later type post mid 60's i think that has bigger main bearings.
headcylinder - 12g295 or 12g206 head would be best they are bit pricey tho as they are rare expect to pay 80-150 for one. 12g940 would fit with modification but with a turbo headgasket failure will be a problem with this. fit hardened exhaust valve seats to the 12g295/206 heads to they will run unleaded morspeed is good place for this.
block - standard 850 block has no white metal bearings for cam and so these ideally would need fitting to 850 block or use 998 block with 998 pistons and 850 crank.
gearbox id use post 1968 box if possible as strounger and will have 4 syncro
best to fit steel flywheel for acceleration
camshaft - pin drive one around 250-260 duration will be best dont go any hotter on 850 turbo it will just make it worse to drive. eg piper bp255, kent md246, med 256, swiftune sw5. i would try standard A+ springs these are 138 lb i think from memory and with standard lift should be fine to around 7000rpm, if not 160lb morspeed ones which should be ok to around 8000rpm but higher the lb the springs the more wear you get and more power loss.
rocker arms, either weld top edge of standard pressed steel rockers and replace rocker shaft, or buy alloy 1:1.3 rockers. dont fit 1:1.5 rockers lift will be too much and power will suffer.
turbo source, if you can find old mg metro turbo they are good source janspeed also did a kit ones this would be best. hulkhead will need modification and it will have big turbo lag. it would be alot easyier to fit and will be nicer to drive with a supercharger as it will have good power from low revs.
dystribitor, standard one will play up with points bounce, aldon should be able to modify or make one up to suit electronic prefrabley
clutch - depending on age of car you will really need to fit higher pressure plate around same as fitted to cooper s should do or you will find you will get clutch slip.
or you could get custom crank made up eg med and destroke 127
Posted: Feb 16, 2008 12:43 PM