Graham Bell’s book “Modern Engine Tuning” gives a lot of test comparisons for various filter makes using test engines. He also tests improving air supple, filter box mods, to get test result figures to show effects. From memory he shows bhp/torque variances from dyno tests. In general the increases appear small-ish and best at higher revs. If you are chasing performance then cold air/freeflow filter is a cheap starting point. Dyno tests will show figures before and after. Will you feel any difference when driving? Maybe if you are empathetic with your car!
My Plus 8 (Gems version) definitely goes better with K&N filter and Shell V-Power, bonnet extenders. In my view anyway!!!
Actually the V-Power has removed an occasional fault code flashing up and I estimate about 1mpg better consumption.
