70 mph.. aha
that's 31.3m/s
let's assume flat level road and a light kart
150 kg * 9.81 m/s² * 0.02 * 31.3 m/s + 0.5 * 1.2 kg/m³ * 0.7 * 0.9 m² * (31.3 m/s)³
means: 12512.263266 Watts
12.5 kW are about 17 hp
you want a bit extra to compensate for all less than ideal circumstances but yeah.
I've seen topped out gx200 in the 20 horse realms, so that'd be doable at least I guess.
Now you want to do that on a very specific chain ratio.. for some likely to be BS reason.
So let's cheat and use the wheeldiameter as our ratio compensation
with 16" wheels that'd require 7400 rpm
with 13" wheels that'd require 9100 rpm
with 11" wheels that'd require 10800 rpm
11k rpm from a stinking predator?
maybe from a tillotson block.. but never a predator..
9k+ rpm? no.. I'd still say no to that cheap chinese clone block I'm afraid
7500 rpm? well finally.. that might work
now the question is how to not only get to 7500 rpms (which is the easy part)
but also to wedge in 34Nm (25ftlbs or whatever) of torque into the engine
that has maybe 10Nm of torque when it left china (8 ftlbs ?)
trippling the torque will be a very challenging part I assume.
but hey, at least you're about to spend almost as much as Mommoth put in his gx390
(money AND effort...)
for maybe half the power
And I'd still vote for a tillotson block if you want that torque not cracking the engine case open on day one.
Maybe some nice cup of overthinking this first?
'sid
