I'm thinking of doing a standalone fuel cell high pressure (43psi) do I need a return or a regulator,or should I do a low psi system?

 

I'd personally do a low pressure dilly, there is a much broader learning base to lean upon when it comes to tuning time. Either system could use a return, the low pressure stuff you can get away without using one however pressure creep may be an issue.

Some people use the pressure creep as a tuning tool when using the system off the line, the higher pressure creates a rich condition that is robbing power for a split second or so and that enables the car a chance to better hook upon initiation of the nitrous hit.

 

I would use a holley blue without a return.....regulate it and things are simple.