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Old 10-21-2003, 12:11 AM   #1
Scooby Specialist
Member#: 5960
Join Date: Apr 2001
Chapter/Region: Tri-State
Location: Atlantic City, NJ
FXT [email protected] 93 oct
NSX 450 whp SC'd (93 oct)

Default Water Injection AND Nitrous???

I just got my Water Injection kit, and am about to install it on my '02 WRX w/TXS Stage 4+ kit w/FP 18g turbo. This is not my only car, so if it broke down, I'd still have other means of transportation ('96 Legacy and '94 Impreza), but I am on stock tranny and stock internals with the '02 WRX. Currently I'm at 20.5-21 psi on 94 octane, running great, and with the WI kit I'll kick it up to 23-24 psi (yes, still stock internals ) and pull as much fuel/add timing as the upcoming dyno tune prudently allows.

Anyway, I'm seriously considering adding a 25-33 shot of nitrous on top of this, but I'm wondering if WI+nitrous is a bad idea. Are the two mutally exclusive? How hard would this set-up be to dyno tune? I just got the remote map selector for my UTEC, so now I'll be able to channel between different UTEC maps on the fly (so to speak). Plus I have an SBC-id boost controller, so I can select 4 different boost settings with the simple push of a button.

So does it make sense to have a 24 psi WI-only map(no nitrous), a 22 psi WI+nitrous map, and a 23 psi + nitrous map (no WI), and a 21 psi non-WI, non-nitrous map, each of which is dyno tuned? Obviously these boost figures are not set in stone, but are my rough figures for each of the 4 scenarios I can run with this set-up, depending on which UTEC map I dial in.

This is not my daily driver, its my weekend/fun car, but it still gets 300+ miles/week (I drive almost 1,000 miles/week all told), and I sometimes do a lot of WOT pulls with the '02, so I dont' baby it, although I shift it gently. Plus I might end up using this car to make some $$$ on the side...but at this point my intentions are more for a street driven monster that eats up V8's, and has a little bit of a hidden nitrous secret just in case someone starts to pull on me....

Also, I have a back up plan, if my motor gives out, I'll do a 2.5L STi shortblock (ah, the joy of being single w/a decent job) but my goal is as "reliable" a 350+ whp set-up as possible. Considering my tranny is stock and I'm already pushing 400 crank hp, I'm assuming the concensus will be that I should upgrade my tranny before doing either WI or nitrous at this point. Let alone my engine internals...

Edit: BTW, my '02 WRX has 76k miles on it Runs strong as hell, though, no signs of issues, but I wanted to mention this fact. The previous owner babied it (I know him personally), and truly did 90% of his 62.5k miles on the highway, and he also ran the VF30 @ a measly 12 psi on the blitz SBC-id, as he wanted to conserve fuel considering his long daily commute to work. One of my first moves was to swap out the VF30 with the 18g that is quite happy up to 25 psi.

Thanks for your opinions, I know I sound crazy, but I just want to weigh out my nitrous options BEFORE actually buying a 25-33 shot nitrous kit,

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Last edited by annointed; 10-21-2003 at 12:36 AM.
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Old 10-21-2003, 12:48 AM   #2
Scooby Specialist
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Join Date: Mar 2003
Chapter/Region: Tri-State
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2006 STi,'11 OBS
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They are not mutually exclusive. They would be difficult to tune together - WI allows reduced fuel/advanced timing from knock suppression - nitrous requires additional fuel/retarded timing from fast burning oxidizer.

I have not worked much with as aggressive as you are getting with WI & nitrous together, with just WI yes but not both. Doesn't mean it can't be done.

My approach would actually be to tune the nitrous alone first then see where you can go with boost, fuel, timing with the WI. Not because of a preference for one over the other just the nature of what the tuning would involve. (I actually prefer WI since it is like a race fuel tune all the time.)

I would also approach it cautiously because of the delicate balance between the two needed - if anything err on the side of keeping the nitrous happy.

You could also ask on my new forum below since you will get responses from those with experiences outside of just Subies.

turboICE Water Injection Forum
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