If they've sold you the turbo on specifications, 'unfit for purpose' I believe is the legal phrase for the situation. Hope it gets sorted for you, I've not heard of someone turbo-ing one of those engines before.

Hopefully this will be just for interest's sake (and it all gets sorted without fuss), but you can check the Sale of Good Act, http://www.opsi.gov.uk/RevisedStatut..._19790054_en_1

This is from paragraph 14:

(3)Where the seller sells goods in the course of a business and the buyer, expressly or by implication, makes known—
(a)to the seller, or
(b)where the purchase price or part of it is payable by instalments and the goods were previously sold by a credit-broker to the seller, to that credit-broker,
any particular purpose for which the goods are being bought, there is an implied term that the goods supplied under the contract are reasonably fit for that purpose, whether or not that is a purpose for which such goods are commonly supplied, except where the circumstances show that the buyer does not rely, or that it is unreasonable for him to rely, on the skill or judgment of the seller or credit-broker.