ORIGINAL: rpg711
I agree, the GX5R is the best engine I have ever owned, grab one of them and a 081 or 053 pipe and break it in as per this guide:
http://go-racing.vpweb.co.nz/TechTips.html
I'm on my 9th tank on this beast and at 1/2-3/4 throttle running EXTREMELY rich with a .2mm breakin shim, it still has 2x more power than my old force .21. Only thing is that you will need a starter box, a worthy investment(I went from needing 10-20 minutes to start to 3 seconds)
The engine that was in was blown so i have no idea of how fast/slow the force .21s were.Main concern is making the car fun, close second is reliability/longevity of the engine then price followed by whatever is left