Thread idea was originally by Blizzard-2000...
I will list all unused engine sounds in Most Wanted.
1-Unused, but there are nodes for them in VltEd:
por_911_b / Porsche 911 Cupcar Orange
aud_s4 / Audi S4
2-Probably just leftovers from UG2:
hum_h1 / Hummer H1
hon_prel / Honda Prelude
3-Haves no node but it's in the game files:
Bronco_Comp (Ford Bronco)
Porsche_Cayenne
Db9_Upgrd (upgraded, high pitch version of DB9 sound)
Por_928_V8 (lower pitch ver of Porsche 928 sound (beta BMW sound))
4-Haves the same sound as the NASCAR Mustang sound:
GTO_65 / Pontiac GTO 65
BMW_450i
(same sound as TVR cerb):
TVR_Chimaera
also, (off-topic?)
I have found some unused cellphone sounds in mw (skip to around 0:13):