There's only so much you can do to the Kyosho GS15 engine. That includes making sure
<LI>its tuned correctly for the conditions</LI>
<LI>the airfilter is cleaned & re-oiled frequently; original item should work ok, you might want to try remove the inside baffle</LI>
<LI>you are using fresh fuel</LI>
<LI>all your bearings are clean & not jammed</LI>[/list]
After that you'll need to spend $$.
<LI>two speed transmission... gives better acceleration</LI>
<LI>universal driveshafts= smoother drivetrain</LI>
<LI>good tyres = better cornering speed</LI>
<LI>tune your suspension... gives better handling</LI>
<LI>new engine with more power</LI>
<LI>new pipe? if you know how to tune it (trial & error) then you might do better, but the stock pipe is pretty ok too</LI>[/list]
Trouble is... most of the V1S that I come across are built for Kyosho Cup competition. There's not much you can do within the Rules, so most of these will sport:-
-very carefully built shocks
-option Kyosho tuned pipe (original works well, but is heavy)
-Kyosho 2-spd transmission, for better acceleration
-good rubber tyres
-thick silicone oils for the diffs
The rest of it...well, some of it is each guys'"secret tricks" but most of them are in the nitro-car RELIABILITY category. These racers run long finals (30, 45, 60 min?) and if your car can't hack the duration, you've got little hope of winning.
More air don't make more power... you burn Fuel to make power, ergo a bigger carburettor will let you flow more fuel+air. But if you're gonna get a new carby, might as well get a new/bigger engine to go with it.
Lighter flywheel don't make anything go any faster - flywheels store kinetic energy, they don't make power. Lighter = less mass = better acceleration... but could also get erratic idling if its too light. (Works on a 1/10 like it does on 1:1.)