You don't need a better engine, that one is fine.
That's a roller cam LA small block and you can start with that block or use a 5.9L. There is nothing wrong with the Magnum series of LA engines and you can bore and stroke one up around 6.6L They respond to the same things that everything else does, like roller cams, performance heads, intakes, and carbs or injection. Add some hardened pushrods, roller rockers, and long tube headers and you'll be on your way. Start by throwing those stock Magnum heads in the trash and ditch the intake too. If you add a stroker rotating assembly you'll get the power earlier and if you add compression you'll get more of everything.
Here is the idea:
In this tech article CAR CRAFT provides a Chrysler LA engine build guide to show you how to build a 500HP small-block Chrysler on a budget of about $5,000 - Car Craft Magazine
www.motortrend.com
Grab a set of these guys:
If you break the bank and go stroker, get even larger runners and valves. 250cfm will get you 500hp, 300cfm will feed 600hp. I put a 200cc runner 270cfm head on a 10.5:1 406ci Chevy and it makes enough torque to rip a house down despite the tall single plane manifold on it, so don't be afraid to go big if you choose to stroke it.
Go for a hydraulic roller cam with maybe around .580" lift and not too much duration. If it's throttle body injected you could grab an Edelbrock Performer RPM Air Gap, a 1" open spacer, and put a self learning FI kit on it like this:
1-3/4 long tubes with 18 of collector extension into an X or H pipe will keep it happy at low RPMs. Depending on cam duration you'll want some gear behind it and a bit higher stall in the converter than stock.
Want Gen4 Hemi like power? You'll need a 315cfm head with 10.5:1 compression, around 400ci, and a cam profile like the usual aftermarket stuff for those engines, say around .600" lift and 220ish/230ish duration. If you can get a good enough head, the only thing that the LA will be missing on a new Hemi is the VVT and MDS. Want a flat torque curve? More displacement is your friend. Good luck!
