"" I believe that dual solenoids are a good idea when running a progressive controller as if one fails and sticks open, it's very unlikely the other one will.""
That sounds good!!
But a second solenoid adds resistance.
The US solenoids do not tend to stick open. They wear on the seat and just let nitrous creep past when they are shut off. That can lead to a problem when you fire the engine up if you have left the bottle turned on.. Ask me how I know
And if you have two identical solenoids which pulse together, why would one fail before the other? I'm not taking the piss, I'm just saying what I think. If there is a known worry about these solenoids sticking open then why use them.
Now lets talk a bit of nitrous tech!
The idea is to deliver as much LIQUID nitrous as possible to the injector or spray plate yes??
Nitrous does not like sudden changes of direction as it makes the liquid change state. The change of state can be from liquid into a super saturated vapour if the turbulence is sufficient enough. This means you are not getting a full head of liquid to where you want it.
So if we reduce the changes in direction, we keep the nitrous in a denser liquid state for longer. In your solenoids the liquid enters the valve body and has to turn 90 degree's upwards towards the valve seat. When its passed through the valve seat it has to change direction by 90 degree's again to exit the valve.
So thats TWO changes of direction you have. Then you have a second solenoid doing the same thing, so thats 4 x 90 degree changes of direction before the nitrous get to the injector or plate.
With the WoN solenoids / pulsoids you only get 1 x 90 degree change in the nitrous flow. And you dont need a back up solenoid for safety
Is your controller capable of pulsing two solenoids ?
I guess that you are using a nitrous spray bar kit ? If so, then how many holes do you have in the bars? ie, is the plate able to flow enough nitrous and fuel ? A good indication of this will be the AFR readings from the dyno. What were they? Can you show us a picture of the dyno data please ?
What car / engine is this?
On my first ever nitrous motor I ran a 50 shot that gave me an extra 75hp (flywheel hp) on the dyno. But that was my first 3.5 litre engine. On my 5 litre engine I could not expect the same could I ?
And there are tranny losses to think about as well ?
My Tranny and rear end saps around 40hp easily on the dyno.
Give us some more information about the car / engine / engine build etc
Regards
Perry