GT45R is "outside the box" by even the most hardcore standards. so, u must have "outside the box" solutions. no more single plate racing clutch, no more piggyback with stock ecu, no more conventional fuel, no more stock rpm range. everything is hardcore.
if u think gt35r is not enough for u, maybe u can try using rear wheel drive cars. it may not clock fast ET time like 4g63 monsters, but it sure is scary n FUN! hehehe