I hooked up my compuiter and GPS up to my 78 280Z. I drove it to a comfortably fast speed which was 118. The only mods are a K&N intake, 8mm wires, 21/1 exhaust w/o CAT. Tires are 215-60-14. MSA ground effects kit. I am going on a 2500 mile drive this next week. I plan on taking it as far as I can handle. When I get back I am installing my MSA springs then I am going for a top speed run again. My speedo was 7 mph off at 118 mph. It was reading 125.
More to come.....

This was on I-84 between Boise and Mountain Home Idaho

 

hey allmyzs we run the same size tire. when I got new tires of the same size on my z I noticed that I still had the original spare. the spare was about 3/4 of an inch taller and that might be some of the problem with the speedo being off.