RE: Good entry level engine for Losi 8ight
Mach 427...
If it has to be a 21, then a Go 21 3, 5, or 7 port.. I've got the new Caster Grenade in my buggy, waiting for a chance to break it in. The Caster is based off the Go 21 5-port, which is supposed to be an awesome engine. The only thing about the Gos from what I hear is that they have insane pinch when new, so you need a good starter box, to preheat them, etc.
For all-out insane power, the best 21 is probably the Jammin 21 JPX - with discount codes you can get them from either tower or amain for around 200 bucks. An 086 pipe and a few turbo plugs would bring that closer to 300.
If you're not racing competitively though, then I'd seriously get another Mach 427. Dead easy to run, not so pipe and plug picky like most 21 race engines(absolute best pipe for a Mach IMO is the stock Losi pipe...)