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Hi Andre or anybody who is familiar using nitrous on turbocharge cars can give me some tips ,
My Subaru STI currently is sitting around 450 to 480 whp on e85 running 28 psi with blouch dom 3 xtr turbo. I think I have pretty much maxed out my setup and just purchased a nitrous express kit last week to add addtional 75 to 100 whp if possible for Drag racing track use only.
So my concern is how much timing and boost do i have to retard for each 50 shot? is the standard rule 2 degrees for every 50 shot still same with turbo cars? Usually i see people retard 2 degrees for 50 shot on pump gas does this still apply with e85 too ?
The only engine modification on my Subaru STI is CP Forge piston drop in and arp head studs,
i only plan to spray at 5000 to to 7000 rpm with nitrous express controller.
Forgot to ask My fuel pump is dw300c 340LPH pump do i need to upgrade this too ? I was told this can handle 700 whp on pump gas.
My spark plug is already 2 step colder from stock as of now should i upgrade again?
I've always worked on the 2 deg per 50 hp rule and never struck any trouble. On E85 you are quite likely going to be able to still optimise the timing to MBT when on the bottle (on pump gas you're more likely to reach the knock limit before MBT on nitrous), but I would always start with retarded timing and then try adding in 1-2 degrees to see if the engine actually picks up power.
Since nitrous is normally supplied at a fixed flow rate, what you find is that the engine will actually ingest more nitrous at low rpm as there is more time for the nitrous to make it into the cylinder. This is why it's not advisable to use nitrous at very low rpm (below 3000 rpm for instance) and it's also smart to remove a little additional timing if you are going to bring in the nitrous at very low rpm.
One thing I'll point out that many overlook is that on a turbo engine nitrous isn't a magic solution to adding power. Yes it will add more oxygen to the combustion charge, however you still need to get rid of the additional exhaust gas and if your turbo is marginal on the exhaust side in terms of flow then you can find that exhaust back pressure climbs dramatically in the high rpm basically choking the engine.
What this often equates to if you're already pushing the turbo very hard without the shot is that on the bottle the engine will show a nice healthy increase in power and torque in the midrange before falling over as rpm increases. Most dedicated turbo/nitrous packages will purposely use a turbo with a larger exhaust wheel and/or A/R to help free up exhaust flow. With the nitrous flowing, spool is not an issue. You can only run it on the dyno and see though.
Hey Andre sorry let me see if i understand you correctly,
your saying by using nitrous with a maxed out turbo already i should only see gains in the mid range like 3 to 5000 RPM and 5k to 7000 rpm wont show much improvements because my turbo exhaust housing size will be choking the engine with nitrous on? Is there anyway to correct this issue besides me buying a new turbo ? I never thought about the choking part on high rpm thats very interesting, i always wonder why people only use it to spool but not on top end, will i experience severe boost creep when the exhuast is back up what will actually happen to the behavior of engine? Will the car just not make good power or will I damage any mechanical component ?
Excessive thermal energy is something I would be mindful of, mass of the combustible mixture as well as peak cylinder pressure come to mind. What that will translate to in reality is something Andre might be more versed to elaborate on based on work experience.
There's no practical way to get around a bottle neck such as restrictive exhaust flow in an internal combustion engine, having said this, perhaps your turbocharger manufacturer might have a solution which doesn't include buying a completely new turbocharger. Maybe there's a turbine solution which favors your setup?
One avenue you might want to look at is the available energy within the fuel being used? The fuel being used is at least partially responsible for releasing the potential energy used to make horsepower, there are other variables which contribute of course but you have to start with a particular fuel in mind to begin with. If you current fuel isn't giving you what you want, at least in a competition scenario which you have described then it might be worth the while looking at another fuel. Of course, this comes with its very own list of short comings so it's a case of picking your poison.
I'm not saying you won't see gains at high rpm, however what you may well see if you're pushing the turbo very hard is that the power gains when on the bottle are larger at low rpm and taper off towards redline. If your wastegate can't cope with the additional exhaust flow then it's also likely that you will see the boost creep up. How bad this all ends up being really depends on your particular turbo setup and you may still find very worthwhile real world gains. I'm not wanting to put you off, but rather making you aware of the possibilities that many overlook. Nitrous isn't like the Fast & Furious and it's not quite as simple as bolting on an extra 100 hp everywhere. It's just another power adder and has its own set of difficulties to overcome.
In my own experience I've typically used nitrous to improve the spool on a large turbo and then switched it off at higher rpm. In NZ a nitrous refill is ridiculously expensive so using the shot just for spool up is a lot more economical on your bottle.
If you're planning to use nitrous regularly though a larger A/R exhaust housing will be a step in the right direction.
Thanks guys i will experiment with 50 shot first and see how my internal wastegates reacts first . I am very lucky when it comes to fuel e85 because its only 3 min from my house, so thats all i use in all of my cars.