How about NO2N20 (No to Nitrous)? I had that as a backup for my Stealth's plate, but got the one I wanted.
or:
GTHEMI (Got Hemi?..Okay, so another letter would definitely help)
NATURL (Natural, referring to Naturally-Aspirated)
BUHBYE (self-explanatory)
M3KILR (M3 Killer) ? Perhaps some variant of that
NOSTNG (No 'Stang)
NOCMRO (No Camaro)
COMPKG (Competition Package or Competition King)
KLRCUDA (Repeat?)
SLOOOW (obviously a lie, but I've seen several guys with that here in the states)
NOBSTG (No Boosting)
BOVWHT (Blow-off valve what?)
PRMLFR (Primal Fear)
PROWLR (Prowler)
JAGUAR (Black, fast car = fast, black feline)
BITES (self-explanatory)
B84ME (Bait For Me)
EFIBST (EFI Beast)
RUMBLE (self-explanatory)
ONPRWL (On Prowl)
BUSTED (self-explanatory)
HDBITE (Heavy-duty Bite)
BYEBNK (Bye Bank...Maybe rather dry for a suggestion)
BYEGSR (Bye GSR...Maybe Bye GSX to keep it within the muscle car era?)
TWSTED (Twisted)
SPEEDIN (Speedin')
NOTOEM (Not OEM)...? I mean as in not having a factory displacement.
FSTFSH (Fast Fish)
Hopefully some of those spark your interest, Carl.