Could be as installed, there are exhaust restrictions that aren't present in a Maxima, sort of how the same engine (the tuned port injected 350s) from a Corvette makes less power in the Camaro due to differences in the exhaust system.
Still...226hp at the wheels in a Sentra is going to be pretty quick. Hopefully you can sort out the tuning and get it out to the drag strip this spring.
