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st170 bottom end silvertop head?
greenwood03 - 4/8/12 at 01:16 PM

quick question......
would a silvertop head fit straight onto a st170 bottom end? or a st170 crank into a silvertop?

short story. crank on my silvertop isn't too clever, to save looking at a steel crank for the silvertop wondering if there are any advantages in looking at buying an st170 engine and using the crank which i believe is steel? or using it in its own bottom end with pistons from my silvertop?

have been looking through the web trying to find the safe tolerances rev wise for an st170 and so far cant find that info....i know an aftermarket steel one would be good for 9-10k revs, realistically looking for safe revving to 8 or 8500. the old eng was/is a decent spec head/pistons/rods but not the crank - hence it not liking too much 8k action. as a new steel one is 12-1400 loooking at options.

appreciate any experience/thoughts.
chrs
mark

paulf - 4/8/12 at 08:58 PM

I would also like to know if a ST170 head would fit onto a black top bottom end, I fancy experimenting with designing a proper mappable VVT controller but at present have a black top engine in my car and it would be convenient to just swap the head to allow me to experiment with it.
Paul

coozer - 4/8/12 at 09:01 PM

No, the cam and crank sprockets are different.

greenwood03 - 4/8/12 at 10:35 PM

coozer - is that 'no' aimed at my original question as the other poster was asking something different.....
was pretty sure i'd seen somewhere that a westie owner had dropped an st170 crank into a b/top.....perhaps i got that wrong....

rusty nuts - 5/8/12 at 08:21 AM

Might be worth comparing the head gaskets or at least see if they are compatable before getting too involved? If the bolt /cylinder spacings and the oil feed line up you may have a chance of it working? Also the pistons might need checking for valve clearance etc. The silvertop uses hydraulic tappets , the blacktop solid , what about the ST 170? I suspect it uses solid, is that going to cause any problems? Would there be a better chance of fitting a blacktop head or is there a reason you want to fit the silvertop?

coozer - 5/8/12 at 10:21 AM

quote:
Originally posted by greenwood03
coozer - is that 'no' aimed at my original question as the other poster was asking something different.....
was pretty sure i'd seen somewhere that a westie owner had dropped an st170 crank into a b/top.....perhaps i got that wrong....


All zetecs cranks are exactly the same. The St170 is the same as all other variants. Rev limit on a ST Focus is 7400rpm, all the books I've read regarding turboing say the cranks is good for 8K, the oil pump being the weak link, and, thats as long as you tidy up the bottom with ARP bolts. Cam belt sprockets are slightly different.

I bought a vernier pulley for the exhaust on mine and the dude at Retoford told me there was a slight difference in diameters of the cam sprockets, using a blacktop one would result in the cam timing gradually creeping out. This was backed up by the RR I took it too.

RetroFord have two different cam verniers in stock, one for blacktops, one for the ST.

[Edited on 5/8/12 by coozer]

greenwood03 - 5/8/12 at 05:44 PM

the reason i'd prefer to use teh silvertop head is that its already been worked on and is fitted with race cams ( so it already has mechanical lifters......
troublke with those cams is that they need to work up to 8k - originally hard cuit was rec by the engine builders ( well known ) at 8100, subsequently i bnrought that down to 7850 to try and look after the engine a bit......bit somewhere along the line inspite of not really doingh many track days ( perhaps 8 in 3 years ) the shells are very badly worn.

coozer - 5/8/12 at 05:46 PM

Should be OK as long as you use a sliver top (or even blacktop) cam pulley on the nose of the crank.