Because it says so in the manual AND if you go to the dealership they usually have a map of what cars use what oils. Most 2001+ use 5w-20.

 

I'm not saying that the dealer does'nt recommend it. I'm just saying that 5W oil is for a broader temperature range for people like you who live in cold weather climates. If you live in Texas, Florida, etc. and the tempertures reach 110 degrees in the summer then you don't want to be using 5W oil on track day. Trust me. I have asked my friend in th eoil business for a more specific explanation and I will post it when he responds.

 

This is what my friend says:

A 5 wt. takes less energy to "sling around" and therefore you will get a small amount of energy savings. My GMC manual recommends a 5w30 engine oil. That is a "northern mentality". Look on the temperature range in this area of the U.S.A. and temperatures ranging from 0*F - 100*F+ can use a 10w30 engine oil. Oils get thin when they get hot. a 10wt. provides more cushion between the moving parts and couple that with our solid lubricant moly to help eliminate wear and reduce friction... it makes for a good match.
You won't find anything as "slippery" and you have the option to go with a base oil from 100% parraffinic, to semi-synthetic, to 100% pure PAO Synthetic.

 

That's a bunch of hogwash. I've used 0w-30 synthetic at track days and during a 2 day track sessions, at autocrosses for 2-3 years no problems. Synthetic oils are not acceptable to thermal breakdown like conventional oils.

 

You did'nt say synthetic. Beside how do you know until you take your block apart. Seems like a dumb risk to me. But your the pro. What is your thinking behind using 0W?

 

Less parasitic friction = more power. When I'm winning and loosing by 1/10th of a second everything helps.

 

Yeah, I guess I can see that but you may be harming your engine. I'd rather gain my tenths in other areas.

 

My car is almost maxed to the rules. I know others who have used 0w-30 and are fine.

 

What about weight reduction, Is that leagal?

 

Only legal items are:
battery, front seats and whatever bolt ons (exhaust, header, intake, wheels, suspension) that are lighter are legal.

I've already done the battery and bolt ons, seats might strip 30lbs.