Is it a HPI Savage your wanting to replace the engine in? That's the category you put it under. If it's a savage I would recommend at least the stock 4.6. That's a heavy truck for a .21. I would recommend at least a .28. I'm not a savage guy though but just from my RC experience that's what I would think.
I own the .30X, .32 and .28. Out of all three the .30x smokes all of them hands down but that's just my opinion. But the .32 is no slouch. From what I have seen the Picco boost .28 is pretty freakin impressive.
Yea, I have 3 .28s and 1 .32. The .32 is perfect for heavy low torque machines like my EK4 that I run it in, but it lacks the upper rpm pull that the .28s have.
I have a few Piccos as well. In stock form, theyre no faster than the LRPs. Modded is a different story.
I have a few LRP 32's and with a XL 3 speed tranny I find it to be plenty even a little to fast being I'm a basher "BUT" for the track its gona suck way to much fuel , lots of pit stops for fuel to win .
If your just out having fun bashing and racing around on a track with your friends you'll be fine with the LRP 32 .