according to greddy they are making just about the same power as the GTM so its really up to preference on who has the better cooling system and intercooler setup. the exhaust is also very critical when building twin turbo cars. you have to remember that each twin turbo is meant to work with each companies own exhaust. taking that into consideration GTM does have what seems to be the better kit due to larger exhaust diameters but im not sure which i would choose because of cooling on these cars is so critical.
