Why am I slow?

[florianz]

The power of the motor is limited by the provided energy. I think everyone has experienced "good" or "excellent" lipos. a battery that performs better under load and thus provides more voltage ("punch") would be an option (4s). there is a lot of marketing, "paper doesn't blush". just a high c rating doen't always have to mean that the lipo has a great punch. for example on this (german) page that guy is testing various lipos. the conclusion of a 20/30c flighpower is, that it performs well up to 15c and is a good 15/20 c but NOT a 20/30c lipo, but permanent 20c is too much http://www.elektromodellflug.de/akku...htpowerevo.htm

just adding a new 3s lipo to get 5s might be a problem, when you're mixing batteries they should be in the same condition/age/capacity/manufacturer.

maybe the esc is also limiting the performance. I mean, going 70+ is not quite usual for that esc.
cool project! I like!