speed is the key
 

i know im going to get a lot of crap for this question but look. noob to the onroad thing, how can i make my hpi rs4 faster. i want topend faster, with out changin my motor. i have the stock .15 and would like more speed on the top. i know it will sacrifice some bottom but thats fine. once again i want to keep my motor, but can modify it jsut dont want to change it.

Go up a tooth on the pinion gears (clutch bell).

Go up a tooth on the pinion
go down a tooth on the spurs
use the largest tires you can find.

shorter pipe.

Pass you soon...

If you have still have stock pipe too, you could/should upgrade it to a tuned pipe as well.

Combustion
 

If you want an engine to produce more power, you can increase the amount of oxygen in the combustion and increase the compression. Ensure your carby is opening fully and that it's inlet manifold isnt choked. If specs permit you may increase (dremel/grind) the size of the inlet manifold to allow more air into the system though this not where Id recommend you start.



Besides the modding of the engine, you can check a few things. Ensure you are getting enough fuel pressure in the fuel delivery systems. Tank nipples, fuel hosing and no exhaust air leaks that will lower fuel pressure.

Then you could toy around with simple timing by trying a colder plug to adjust the ignition timing and also ensure that you are getting a clean burn by checking the condition of the cylinder.

You could increase compression by removing shims but this depends on the amount of oxygen in the air. Things to take into consideration are the temperature of the air, the altitude and humidity. And like the previous response improve the back pressure effect by using a tuned pipe.

The obvious best method if these minor changes arent working is to accept that the engine isnt hi performance and buy a more powerful engine.

You could also try different fuel.

ok do with the gearing. does anyone know what the stock gearing is. i believe i have the rs4 3, if your looking at the car from the front, the engine is on your left rear. it came with a plastic pipe, even platic turnbuckles for some reason. now, i do not know what number of teeth are on my spurs, reason being is my motor came loose one day and completely stripped the teeth off one off the gears. so i need to know the stock teeth size so i can go up or down from there. also, would a .15 off my rc10gt rtr be faster or stronger then the .15 that came with my rs4?.