RE: what engine to fit in my RS4
If you want speed on a low budget, I'd say go with what Foxy suggested and get that 18TZ. Im a very strong believer of that motor, specially in smaller, lighter cars. I ran a fully modded Novarossi 12 in a Racer2 which is an upgraded RS4 and achieved 82mph which is really good for a 12. Then later gave the 18TZ a shot with the same gearing and got a screaming 85. Geared up and managed a best of 92 but locally. This is the same ISC car that went 90 at the event. So in short, the OS is the best and easiest to tune small motor I've ever dealt with.