Ok, so if your car is stock and used on the road, this doesn't apply to you so don't bother reading it unless it is of interest -
If you have "modded" your car and added BHP or you use it on track or drive it hard then it is vitally important that you consider your oil choice carefully as the stock manufacturers recommended oil will not give you the protection that your engine requires.
This is because your car is operating outside of the OEM's oil recommendation envvelope.
A standard oil (semi-synthetic, mineral or even a hydrocracked synthetic i.e. not a true one) will not be thermally stable enough to cope with higher engine temperatures and stresses without "shearing" (losing viscosity)meaning that the oil will not give the same protection after a couple of thousand miles as it it when it was new.
Let’s start with the fundamentals.
An engine is a device for converting fuel into motive power. Car enthusiasts get so deep into the details they lose sight of this!
To get more power, an engine must be modified such that it converts more fuel per minute into power than it did in standard form. To produce 6.6 million foot-pounds per minute of power (ie 200 BHP) a modern engine will burn about 0.5 litres of fuel per minute.(Equivalent to 18mpg at 120mph).
So, to increase this output to 300BHP or 9.9 million foot-pounds per minute it must be modified to burn (in theory) 0.75 litres.
However, fuel efficiency often goes out of the window when power is the only consideration, so the true fuel burn will be rather more than 0.75 litres/min.
That’s the fundamental point, here’s the fundamental
problem:
Less than 30% of the fuel (assuming it’s petrol) is converted to all those foot-pounds. The rest is thrown away as waste heat. True, most of it goes down the exhaust, but over 10% has to be eliminated from the engine internals, and the first line of defence is the oil.
More power means a bigger heat elimination
problem. Every component runs hotter; For instance, piston crowns and rings will be running at
280-300C instead of a more normal 240-260C, so it is essential that the oil films on cylinder walls provide an efficient heat path to the block casting, and finally to the coolant.
Any breakdown or carbonisation of the oil will restrict the heat transfer area, leading to serious overheating in the engine.
A modern synthetic lubricant based on true temperature-resistant synthetics (pao/ester man made) is essential for long-term reliability. At 250C+, a mineral or hydrocracked mineral oil (like 90% of oils labelled synthetic out there and cheap synthetics), particularly a 5W/X or 10W/X grade, is surprisingly volatile, and an oil film around this temperature will be severely depleted by evaporation loss.
Back in the 1970's the solution was to use a thick oil, typically 20W/50; in the late 1980's 10W/60 grades were used. But in modern very high RPM engines with efficient high-delivery oil pumps thick oils waste power, and impede heat transfer in some situations.
A light viscosity (5w-40 or 10w-50) good synthetic formulated for severe competition use is the best, logical and intelligent choice in these situations.
Don't be fooled by that buzzword "synthetic" as most of the cheap ones on the shelves today are not, they are in fact highly refined mineral oils and although suitable for stock road cars, they are just not thermally stable enough or of the quality required if your engine is more stressed than a stock engine.
I've said it so many times but you don't need a 10w-60 and you should look at a proper synthetic oil in these situations.
Ahh but they cost too much I hear you say...................
Well, it's simple:
They are much cheaper than an engine rebuild and in comparison to the running costs of your car, an additional £50 per year is a small price to pay! Moqueur
If you got through all of that, thanks for reading Clap
Feel free to ask questions Clin d'oeil
Cheers
Simon
at our firm, you can go in with a payslip from regonised garage and a credit card for I.D and you should walk away with 1 as thats on the requirement list or if you speak nice at a branch, we just select managers choice, its up to you if you want one, sorry i cant 
