How fast can you make a graupner key west go with a 700 bb and a flex drive system,Will they handle much speed without doing a bunch of mods

Without modding the hull, about 40-45 Km/h, maybe a bit more.
The stock hull comes with molded in "breaks", at the rear part of the sponsons, these need to be filled and flattened so the hull runs more free.
I've seen Key West doing an astonishing 80Km/h+, but the hull was glasscloth/epoxy re-inforced, the rudder offset and very shallow (low drag) and it had a brushless motor and modded prop...
Just the shape was original, sort off, even the hatch was modified to be really waterproof.

Regards, Jan.

P.S.: why bother with an outdated design, when there are so many epoxy hulls available, that will run much faster...

what other hulls are you talking about and where to buy them thanks

I can only recommend what I know, the cats from: Hydro & Marine, Gundert, Ralf Schnippkoweit, MHZ, just to name a few.

What's available to you in the US as far as Fast Electric cats go, I'll let the other experts advice you.

Regards, Jan.

Scatcat 26 from BBYracing.com is a good choice hers here for a complete setup article www.rcboataholic.com