Is it special then , Ive seen it twice and sounds differnt to the other PCs , but departing reading it sounded like an MTU but clagged

hock:.
It was BR's second attempt at re-engining the class 43 PC's, the first attempt was with a Mirrless 12MB190 rated at 2400hp fitted to 43167/168/169/170 in the mid 80's(managed to get a pair of these on a set and did they go!), these weren't very successful mainly due to Mirrless withdrawing the engine design from their range, 168 was the last PC to carry it in about '96.
About the same time Paxman's had designed a new diesel mainly for industrial app's but were keen to do a traction version (slightly de-rated) and approached BR in their final years, the first of these V12 engines(de-rated from 2700hp to 2250hp for the HST) was fitted into 43170 and named GEC Paxman, this engine differed from the Valenta in being a 90degree engine but also differed by instead of fitting one large turbo (the scream on a valenta!) 6 smaller automotive turbo's were fitted, the valenta's had a habit of eating the napier turbo's and at over £20k for a replacement were keen to address this!
All 4 Mirrless fitted PC's were retrofitted with the VP, with 167 going to the ECML for trials (and eventually converted back to a Valenta) after a PC swap, several others were fitted but despite promises's of lower fuel/oil consumption never really lived up to it, MML converted some of their fleet and are about to re-engine the remainder with the VP185.
incidently the 12VP185 in 170 is an updated version and looks like staying almost to the end (was at Pad last night on the london end)
Mirrless 12MB190
http://www.oldengine.org/members/blkstone/History7.htm
Paxman 12VP185
http://www.nelmes.fsnet.co.uk/paxman/paxeng34.htm#vp185