WElife, i had the ho4.6 in my hf and it went ok, lots of low torque and good top speed (nothing like the top engines though).I read on another forum the ho4.6 doesnt provide as much power as the standard4.6 but there isnt much difference. I assume the savage would be heavier than the hf so i dont see how the savage would be faster unless you arent tuned correctly or your engine has lost compression etc. Although i did read the savage x is advertised at going 70+ kms/hr? the rtr hf does only about 60k/hr. The hf should handle alot better than the savage. My ho4.6 has about 6 gal through it and still running good but i have the os28 in it now, ballistic.

Nitrofarmer, the hf has many diff issues. Unless you have shimmed correctly your diffs wont last long. I have stripped many pinions and the plastic diff cases warp if not shimmed right. I dont know if the diff is your problem but highly likely. What diff oils you running? If you hold the spur gear tight and push the hf do you hear clicking noises from the diffs and the wheels move on each click?