There are several reasons for the propane.
1) To get my car thru registration it eliminates all the emissions crap.
2) Cost of operation. Car is daily driver.
3) Environmental factors of propane v fuel.
4) A correctly built propane engine is comparable to a fuel engine as far as power delivery. A 450 hp 460 costs about the same to build but about a third to run. There are some things to consider but that is more due to a lack of existing hipo prop installations versus the number of parts and info you can get for a fuel motor.
5) Superior engine life.
6) Safer in a vehicle accident.
Anyway.. off the pulpit now....
I cant use fuel as that breaches some restrictions I have. I could do it for a track only option, but there is no logical reason why I should have to do this. Propane is just the same as any other fuel. I would be adding a third fuel delivery system where I really only need 2.
There was a guy near my place who made a custom n2o setup on his 351 straight propane car which from independant reports was a stunning performer. Unfortunately he is no longer in business and I cant find him. It sprayed liquid LP and n2o into an adaptor above the throttle plate. I can do this too, but dont know how much to start with.
There is less detonation with prop than fuel.
Prop has an octane of 104. It is actually a great fuel for boosted motors. it also absorbs heat as it changes from liquid to vapour and the fuel doesnt fall out of the air and form droplets like wet fuel in a large plenum intake at low air speeds.
There is a risk of damage to the motor, but I think thats the case for any n2o setup. If I can find another person who has done it then most of the risk will be taken away I think.
What are the startup considerations for a fuel and n2o motor? How many pounds of fuel is required for each pound of n2o for example to maintain the mixture.