The way I see it, it necessarily isn't just the displacement that makes a car get bigger gains from mods. I think the way a car is tuned from the factory makes a big difference.


About the GSR's times, they do seem rather slow. If you want to rule out the driver being the case, try switching drivers.

If it isn't the driver, then the work done to the GSR is probably to blame. Who did the headwork and other engine work? What was actually done? Did they actually have a plan or did they just say throw a bunch of things together that weren't necessarily tuned to work well together?