I wouldn't take the dealers advise mate, if you type your reg in on Castrol's website the only oil they recommend is 5w30 Fully synthetic. I speak to quite a lot of people involved in Motorsport through work and they all recommend either Millers or Red line oil brand-wise.
I contacted Millers and told them that the dealers in all their wisdom had put 10w40 semi in my car when they serviced it, and was told that oil is no good for these engines, I also told him its been remapped and I have plans to further increase the power and torque and he sent my the data sheet for their highest quality 5w30 fully synthetic oil which he 100% recommends for these engines especially if the re-mapped. My uncle runs a chain of motor factors and I've asked him to order some in but they have to buy a minimum of 4 as that's how many come in a box, so next week I will be doing an oil change for the good stuff, but will have 3 full gallon bottles remaining if anyone else is interested, if so pm me.
I'll post any results on here after I've changed it.
Jack.
Thanks duzza, do you think it's worth me asking the dealer to put the correct type I'm?