no, propane would have the same effect as the nitrous, just without as much bang.
adding propane woudl just lean it out even more.
Whenever you run nitrous to a gasoline burning engine you need to add gasoline to richen up the mixture.
Nitrous is not flammable and it acts as an accelerant to the gasoline making it burn a lot faster and hotter.
since the nitrous acts as an accelerant, you need to add more gas...more gas, burning twice as fast as normal equals big power.
the more gas you can cram into the cylinder, the bigger than bang will be and the more power it will make.
the nitrous helps the gas burn faster which increases power and rate at which the engine will make rpms.
adding nitrous by itself will lean out the mixture too much and can burn a hole in the piston.
I've had 3 drag cars, all with nitrous so i have experience playing around with it.
when you run a lot of nitrous (like 150 horsepower & up) you have to add a separate fuel pump just for the gasoline solenoid.
so you have the fuel pump for the engine by itself, and then you have a solenoid for the nitrous. Then you have a separate electric fuel pump and solenoid for the extra gasoline needed for the nitrous. Everything must be under pressure because it gets injected into the engine through jets and a spray bar under the carb. on a car engine, you have to be runnign at least 7 psi of fuel pressure for the nitrous, but the nitrous itself comes out at like 850 psi.
you have to have a steel crank and forged pistons when you run 150 or more h.p. of nitrous because it can be very hard on the pistons and the crankshaft.