they run supper strong, pretty much the same as the 860. dominate over the 800. but... in order to get the 840 to fit the the cylinder walls start to get pretty thin. it has been a couple years now but the one i saw ended up seizing the motor and cracking the cylinders. pretty much wasted the motor. i guess the 860's aren't as thin since they start with larger cylinders in the first place, so they are preferred. this same 840 that i was around never did run correctly, he had lots of trouble with it and the seized motor was the last straw. but keep in mind this was at sea level, which changed the runability of the motor. carl's did all of their testing at higher elevations and i heard had them running very well up high. my experience was only with one person's sled. (although he is the most competent tuner i know, and is personal friends with Jack. so he knew what he was doing. not just some dude with more money than sense...) if it runs well, it would be an absolute ripper. i'd get more details about the specific sled and call carl's and see what they say. good luck.
pv
