mastermind

i have a 1991 LS400 and i had an urge to race some honda 4bangers. i killed this one car, i coulndt tell how fast i was going since my speedometer is dead, but the car just stalled going atleast 85mph+ abit and i felt no power or the engine reving (pedal to the floor all the way of course) then later i raced another, i got out of 1st gear and then on 2nd gear at around 5000rpms it did the samething.

this ever happen to any of you or do u know what it is?