There's no real way to tell as there's not a speedometer in the game to tell, but the speed is not really effected by upgrades, only the acceleration is.

I believe it does, it goes pretty quick as a car itself.

thanks guys for the help on that just wanted to know

Entity is a better car because its acceleration is insane if they were to race the entity would win

if it was a longer reace straight away know acceleration is only acceleration adder 10 mph better think about it but turns and all probably with a good driver it would be nice race both maxed be close

None of the cars reach their "top speed", the fastest I have been in a car on GTA is 155mph in the Cheetah, bearing in mind I have all available upgrades with maxxed out Adder, Entity, Turismo, Vecca, Cheetah, Carbonizaire, Infernus, Jester, some muscle car and a Bati 801.

You can see the fastest you have been in a vehicle somewhere on your stats as well as the vehicle you achieved the speed in.

yeah i know they really need to fix that because i think its stupid it shows how fast it goes but you really don't go that fast but then i could see that since crashing or hitting a car or something stupid like that to stop you going that fast you know but adder great car.

its says the fastest ive gone is 299 in a cop car

jaypitts wrote its says the fastest ive gone is 299 in a cop car

Except you didn't, especially not in a stock INTERCEPTOR. I went 147 in a maxed out Sultan with NOS, and I've never gotten faster -- not in a maxed Adder, not in a Cheetah or Entity either.