Right now the most tried and true ESC for conversions ironically has been to modify the Mamba Max ESC from castle creations to work with 4S usage. It doesn't take much work to do, and if for some reason you eventually kill the ESC, its only $50 for a no questions ask BRAND NEW replacement. These converted ESCs actually work quite well.
Next in line I would have to say would be the Mamba Monster ESC V3 version. I am lucky, I still have a V1 MMM that works fine. Others have had issues, but it appears the V3s have corrected the problems. For the money, about $150 online, its one heck of a unit, and castle stands behind there products.
The Tekin ESC I have heard works very well, a bit pricey but never the less you get Tekins excellent quality too. Tekin also have a 1/8 scale ESC in the works.
Novaks HV ESC setup appears to work if you gear it CORRECTLY and use a mild Novak motor, say 7.5 or higher. I think with even lower KV motors, the novaks will prove more reliable.
Finally, Losi's ESC for 1/8 scale. Have heard good things about it. Still pretty new, but so far, so good.
There are lots of good choices for you.
Now, as for motor, I would go with something in the lower 2000Kv range on 4S. the really powerful 1.5D 1512 is overkill IMHO. A pig on power, and you need really good batteries to handle the draw of the motor. People have puffed Enerland based cells (some of the best) 25C 6000mah packs on this motor.
A good motor for 1/8 scale buggy would be the Neu 1512 2.5D motor. its 2050Kv, excellent speed and performance on 4S, and also performs well with 5S usage. If you are looking for one of these, drop me a pm as I have one I am selling since I already have another motor.
As for battery pack, depends on what kind of conversion you are doing. Regardless, go with something 20C or better in the 5000mah and up range for 4S usage.
There are some really good packs out there now for the money.
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