Ive had a Gtp and it very capible of doing high 13's with the right tires/driver( intake,pulley,exhaust)... best mine did was 14.2 ...not great....
Gs-R can be quite fast for little cars.... on my g tech my buddy did a 6.35 0-100 --- headers / exhaust/ intake .... pretty impressive....
Best ive done was a 5.04 0-100 with my 18's on ..... i want 4.9 !!!
ex bimmer man/ex subaru man turned Dual V8's Jeep&Vette