i have the engine that came in my rc10gt plus rtr. is the engine worth rebuilding or modifying? should i change some parts(i.e. cooling head or whatever), or should i do a total rebuild, or should i just replace it? it is still new i just want more speed and a better engine, plus i love working on it.

Polishing the intake and exhaust ports or boring them out will increase the power signifigantly (don't mind the spelling). It requires many hours of practice and many new pistons and sleeves to practice on. The Associated engine is certainly worth rebuilding. You shouldn't have to get a new engine but, you can never have too much power!

hey why is everyone talkin about .12 engines -

why not.15 or.21 for speed?????????

and whats a 5 port mean - or diff. size ports? - and whats rb?

.12 engines are important because they are the only knid that you can legally race in competition.

And because .12 are made for RPM, where as in a .15 or .21 torque is their main purpose. Plus a .21 would be a bit of tight squeeze for a stadium truck.

Are you referng to RB Concepts? They make killer engins and tuned pipes.

Five ports refers to the amount of intake and exhaust ports in a sleeve. When they are bigger or wider, it make it easier for the engine to "breath", hence giving it more power.

Since you want more power, I would not suggest a rebuild for your current engine.
I suggest that you look into a new engine that will provide more power. Something like the O.S engines CVR and the new O.S models would be a good choice. TowerHobbies sells versions that come with the shaft already cut, a (S) depicted in the product I.D. means that the shaft has been pre-cut to drop right in to your RC10GT.
You could also look into the Nova Rossi Engines such as the MUGEN MT-12, it is one of the most powerful and most reliable engines in its class.

As for the modifications, Its very easy to ruin a engine , If you want to learn I suggest you find some older used engines to practice on.

Dbow