VP
A couple years ago, used it on a 421 SBC 1050 dominator in 2600# S-10.
On regular alky ran 6.10-6.20 range in 1/8 mile at 120MPH.
Changed nothing but M5. Ran 5.80-5.90 at 125 MPH.
EGT went up 50 degrees.
Recently on a 532 BBC pulling tractor switching to M5 netted 5 out of 8 wins, until getting repeatedly protested.
Just make sure an enclosed vehicle is really sealed up good or the fumes will be very bad.
Also need to drain and run regular alky thru system after each use, sepecially on a carb.