Hi Steve,
Welcome to my forum and I'm pleased to hear that you've;
1) Appreciated that there are far too many 'experts' out there
2) Seen that there is GOOD information provided on my forum
3) Realised that you chose the wrong nitrous system
All of which means you're at least trying to move in the right direction despite a bad start.
Your engine sounds like it could handle a decent amount of nitrous, as long as it was delivered by a CORRECTLY DESIGNED nitrous system. The problem is that as you already appreciate, you are currently lacking that key ingredient to achieve such high levels of reliable power.
The main problems with ALL other nitrous kits are;
1) Nitrous reaches the engine much quicker than the fuel does - this causes an initial extremely lean condition (which is worse the bigger the jets you use), that puts the engine in 'thermal shock' (on the edge of detonation) for the entire run, which ultimately will result in engine component failure.
This is NOT the case with WON, as our controller has a nitrous only delay feature to ensure that even a badly fitted system will not suffer from it. 2) Distribution is TERRIBLE - using jets at the nozzles is the way they 'ATTEMPT' to correct inherently poor distribution due to a lack of correct components/system design and although that helps, it still fails to do what correctly designs components/systems can achieve in that regard.
This is NOT the case with WON, as ALL our components and systems are DESIGNED to achieve PERFECT distribution and to prove it we do NOT locate our metering jets at the nozzles, we just locate a single metering jet at each Pulsoid outlet. 3) Loss of density is substantial - this has a number of detrimental effect but the end result is that an engine will make less power from a given amount of nitrous and it will have a much lower power limit, before detonation sets in and kills it.
This is NOT the case with WON, as ALL our components and systems are DESIGNED to minimise loss of density. As a consequence of all the above problems with ALL other brands of nitrous kits, ALL engines will be limited to adding much less nitrous, than they would be able to handle with a WON system.
To make matters worse, for every engine/component there is a variation in capability, so one con rod might be able to handle say 100 HP while the one next to it might be able to handle 110 HP and there is no way of knowing what every part can handle, until it is too late.
With all the above in mind, it is impossible for anyone to give you the kind of answer you want to your question and that would even be the case if you had a WON system, as all I could say for sure, is it would be higher with WON than what you already have.
It's for these reasons that we always advise our customers to start at a modest power level and work up in relatively small steps, because that at least should help you to get familiar with what the engine should sound like when its happy and when it starts to sound any different, you need to stop and investigate, before killing something.
With regards to adding a controller, yes that does increase the level of power that your engine can handle BUT with ALL other kits it exacerbates some of the problems mentioned above, like the fact that each time the solenoids are opened (pulsed), the nitrous reaches the engine long before the fuel (and also gets way out of sync), so that obviously doesn't help reliability.
Again this is NOT the case with a WON system, as we have specifically designed our Pulsoids for pulsing (hence the name) and we use other UNIQUE system features (jet location, pipe size, etc.) to achieve reliable results when pulsing.BTW the reason you can add more as rpm increases, is because as rpm rises the induction time reduces and therefore LESS nitrous would flow into the cylinder on EACH INDUCTION CYCLE, when using a FIXED nitrous delivery. If your engine can handle say 50 HP at say 1,000 rpm it should IN THEORY (excluding the fact that inertia loadings increase exponentially) be able to handle 250 HP at 5,000 rpm. While this is generally not the case IN PRACTICE, there is a middle ground that does apply.