two engines which is putting out more

Mini Bike & Go-Kart Parts

Depends on the type of racing.
The bigger engine will always get off the line and out of the corners faster because its got a lot more torque.

The smaller is lighter and make more power in a higher rpm range.
Under the right conditions it going to be able to chase the big motor down if it can stay in and turn its best RPM

Short list:
for the small motor.
Honda GXV160 flywheel $70.
14cc clone head $20.
flat top piston and rings $7
Cam $60
Billet rod $60
G200 spring $4

Thats about $350 worth of parts depending on where you get or scavenge them.
To that I would add upgraded valve train for reliability.
Now costs is rising to 425 just for the parts......
And the carb sucks so add more money....
And the choices of header at another 50.....
And you st need a engine to put these one......

Back to the GX390 clone....
Look at the costs involved.
Go to HF and price the 420 pred
420 cc OHV Horizontal Shaft Gas Engine - Certified for California

Add the unifilter and correct jetting, header, and leave the governer intact.
Thats cheaper and does the same thing.

But the big block is very big and heavy....
It will however do what a built clone does or less money.