my camaro the previous owner replaced the engine and now this engine has 48k and my friends gto has only 58k

But dont u think that weight deals a big part in this?

 

It's true the GTO is heavier, but a 4th Gen isn't considered a "light" car. An LS1 GTO should be running mid to high 13's if the person can drive. Your car stock should be running low 14's, maybe high 13's if you're good, with the mods you have you should be able to break into the 13's. You have mods similar to me and I've run a 13.6 (if I were at sea level), I would say you're probalby a bit slower since you're running shorties and not long tubes...