mtx-4 have dog bones,urethan belts, the front uprights(steering blocks) are o degrees,the outside belt tensioner is on back direction, the mount of the rear camber liks are bigger, the engine mounts aren't aluminum and single brake disc, frot one way or solid front diff(two diffrent parts),aluminum bell pinions.
mtx-4r have cvd's,rubber belts,front uprights(steeringblcks) 2 degrees,front lower control arms have a modification because of the steeringblocks,belt tensiones on front directions(when taking the engine out you don't need to take off the tensiones), aluminum engine mounts,rear camber link arm mount smaller(camber moore agressive when cornering),ventilated double brake disc(like the 1/8), one way/solid front diff(one part, just remove 2 pins and is oneway, insert 2 pins and is solid diff without changing any part),new harder material and lightweight bell pinions.
improvement: moore steering, moore options for setting,moore braking capabilities when needed, in resume a better car , moore agresive and still stable on cornering. best car I ever drive
all mugen driver's if i forgot something please correct me