I have a 2008 Pontiac G8 V6, and I am looking at getting a set of your manifold insulators,I am curious as to which size will fit my car?

If you have a 2008 Pontiac G8 with split engine covers, then the 25mm manifold insulator will fit. If you have a 2009 Pontiac G8 (essentially a MY09.5 VE Commodore) with the single engine cover then you'll only be able to install the 12mm manifold insulator.