thats a tough one. a 250 will, but i think a 400 would be a bit too tight..cases would fit as they are same as they 250 basically, but you would struggle with the top end and the rest of it. with a 250 in a 175 floater the carby is allready a tight fit and the bigger barrel of the 400 would space the carburettor back further. nothing is impossible so i think someone with mechanical and welding skills could maybe do it,i think it could be a little too much power for that chassis too? but ive also heard of a RM 500 in a 125 frame aswell, so dont know? the other recommened mod is to then also fit a bigger rear rim and tyre when fitting the 250 motor.
theres always a few PE 250 and 400's on ebay, maybe they would be a better option if you really want more power? many expert enduro PE riders such as Geoff Udy (he still has a 400 and may be riding a few vinduros soon, so im told) have said the 80/81/82 twin shock PEs were better than the full floater rear on the 175 when the std twin shocks shocks were replaced with a good set of french DeCarbons or some Ohlins. the twin shock geometry on the later PE's was at the pinicle of twin shock design, and isnt all that bad.
