SB Road Racing/Nascar/Sprint Car/Reving BUDGET BUILD

You don't want a 318 with 273 heads and an RV cam in something that goes to a track. You'll be getting your *** handed to you by stock NB2 Miatas... on the straights.

Stock bottom end 360 Magnum will handle about 500 HP all day long but to make that kind of power you'll need aftermarket heads for sure in addition to cam and intake, obviously.

The '70 Duster in my avatar has been my long-term work-in-progress road racing car. The current engine is a stock 5.9L Magnum short block (pistons, crank, rods) with ported Edelbrock RPM heads, RPM intake, custom-grind Racer Brown hydraulic roller cam and shorty headers. Around 9:1 compression. It recently did a 1/4-mile pass in 12.65 seconds at 108 mph which translates to around 450 HP at the crank. It would probably pick up 20-40 HP with a set of long tube headers which I own (Doug's D-453) but have yet to install. It also needs a more race-oriented carb, the 750 cfm Street Demon works OK but I either need to go to a carb with bigger bowls or upgrade the fuel system for more flow as it leans out wide-open at higher RPM.

BTW I shift at only about 5500 RPM. SBMs make a lot of torque for the displacement (especially 360s) so they don't need much RPM to hit 400-500 HP. Remember power is just torque times RPM divided by some constant (5252 for HP and lb-ft).

I agree with @rmchrgr though, just put the G3 Hemi in and keep it stock for now. It'll make a bit over 400 HP which is plenty manageable if you do the proper chassis, suspension and brake mods to handle it. I've actually never driven a sports car and my Duster is the only thing I've driven on a road course or autocross. The key is simply not to give it full throttle all the time, start slow and work your way up to find the limits of the car. I've ridden with friends in their Miatas and other small underpowered stuff and they use the gas pedal like an on-off switch and shift like they're trying to rip the transmission out of the car.