the engine you choose is gonna depend on you,youre driving style.and thensize of youre track. if you run a small to medium size track then a stock or modded p5 with a low to med torque pipe will be plenty. if you run on a med to large track then the options open up. you can try a modded p5 with a jp2 high torque pipe or you can jump to a rossi 421b 8 port engine wich is what i just bought for large tracks and try a low torque pipe so you will gain low end grunt and still have top end speed due to the 8 port sleeve. now if fuel milage isnt a concern then a rossi 28 is a good choice for med to large tracks but i would run a jp2 pipe with a 15 tooth clucth bell and a smaller carb restricter to smooth the power curve uot cause that mill is brutle fast almost to fast and it sucks down fuel like no other im talken 5-6min. this is just my opinion my choice would be a 421b for the tracks i run on and cause it will get good fuel run times and is blistering fast and very dependable and only 329.00 at amainhobbies.com. my second choice would be a hot mod p5 and then the rex 28. all 3 mills are great mills and you wont go wrong with any but some may suit better for some tracks than others so it really boils down to you and youre track size. good luck.