I have been doing a lot of reading lately to educate myself about nitrous so that I can make the right decision for my application.
I am currently leaning toward a dry shot kit but there is one question that I need answered and I can't seem to find it in any of my searches.
Since a dry shot requires additional fueling from the injectors I wanted to be sure that my current stock ones would suffice. I went through several of my HPT log files to determine my injector duty cycle % on numerous WOT runs and the car runs 80% with peaks of 86-87% just prior to the 1-2 and 2-3 shift.
My question is will my inj. support the additional fuel with a max. 100hp shot? Does anyone have log files from an NA and N2O run that could see the difference in duty cycles with stock 99 injs. on a 75hp and 100hp hit?

 

Beer, a member here, has been logging % duty cycle, and recently swapped to a bigger injector for his dry shot.

I'm sure he will chime in, but if not you should contact him, as he will be able to steer you in the right direction.
Vinny

 

Thanks, I will do that.

 

Also, check this out. This was in a thread several days back. Nice calculator to start with.

http://www.rceng.com/technical.htm

 

I don't think you will. N/A at 80% duty cycle will go static on a 100 shot, never tried a 75, but I would think it would also max them out.

Matt

 

Yes you can run a 100 shot on your 26lb inj. However, it will put you into static flow, over 100%. Is it a problem for running 1320'? No, or shouldn't be. Would it be ok for a roll race or street race longer than 1320'? No, I wouldn't do it. The time that the inj. will actually spend over at, or over 100% will be very little in a 1/4mi, heating of the fuel wont really be an issue, but as always its never recommended to push something to and beyond its limits.
Dont listen to the "well if your pushing your injectors past 80% and one fails your fucked" posts. If your cruising at 22% and one fails and you dont know it, or WOT at 40% and one fails your fucked!

 

True, you can, but if you do, spray it on a dyno with a wideband or get a wideband in the vehicle. With the dry kits gaining popularity we've seen more and more stock injector vehicles hitting static and going lean on the dyno, especially in the higher mileage vehicles. In all cases swapping out to a larger set of injectors richened the A/F back up to where it should be.

Matt

 

From what I learned, with the dry shot the nozzle position is critical. Vinny @ 860 helped me set up my system and we found that with a 75 shot I went lean with my factory 99 26 # injectors. A 50 shot was a sweet 11.x AFR, but when we went up to a 75 the AFR was 13.5.

Todd is running a dry system on his 99 and had an AFR in the 11's with a 100 shot.

The biggest difference in our installs is nozzle location, Todd is spraying two dry nozzles directly at the MAF, I am spraying two nozzles through my Blackwing "around the corner" so to speak.

My Injector duty cycle with a 50 shot was 106% or so, I am sure Todds is above that with his 100 shot, but it is working quite well for him.

The rule of thumb from what I have read is 85% duty cycle or less is good number to use to ensure longevity of the injectors. From what I understand you can go over 100% (as I did), this makes them static (wide open) and may make the injectors hot and possibly prone to failure with continued abuse.

I got a set of 42 Delphi's from Matt @ HSW and now I am spraying 100 dry @ 60% Injector Duty Cycle or so, and its in the low 11's for AFR.

My advise from what I learned is you can spray 100 with the smaller injectors, but ensure you have the dry nozzles pointing right at the MAF just as Todd did. Also when testing the system, increase the shot size in increments; my 50 was fine, and we went to a 75 and it was way lean. 25 difference in the shot size was a drastic difference in AFR.

First day home, yesterday was a travel day Gotta put the HSW hoses on the dry plumbing reroute, and swap to an LS6 intake, and put the port TB on, play with the tune, panels, panels, and more panels...so many things to do...so little time

Beer

 

Thanks to everyone for the help. I think that I will just upgrade the injectors to be safe. I'm sure I can find a used set locally. Now begins the search on how to tune for larger injectors. LOL

 

Here's the basic math for figuring the injector size.
(Projected Flywheel Hp x .5) / 6.4 = Min Inj to meet 80% rule.

The 80% rule is more for longevity concerns, meaning a continuse use basis. So, I agree with cat, going over 80% in a 1/4 run really means nothing, unless you go so far as to lean the car out. So, being a little bigger when chosing injectors is not a bad idea. I currently run the SVO 42lb'ers, which are a little bigger than the ones Beer uses (they actually are about 47/48lb'ers at our pressure), and I have not seen over 80% at 250rwhp shot. I also normally get a 11.5:1 a/f ratio with a straight nozzle and one 90* on my intake (dual nozzle), and close to maf about 3 or 4 inches.
I ran stock injectors (28s) and a 135hp dry shot to 480rwhp and had no real issues, except was running out of injector, and do not rec anyone doing this unless they have a WB and logging DC.
Robert

 

Well one of the local guys that I thought had an extra set of 42# injectors informed me he sold them a while ago and I really don't want to spend another 4400ish for injectors so here is my question.
Based on some of the advise I recieved in this thread will I be okay to just run the stock 26# injectors without harming anything if I only intend to spray the car at the track, each track visit will only see a handful of passes on the bottle until the pressure gets too low and I only get to the track 5-6 times a year.
BTW, I may be able to get 02 stock 28# injectors will it make any difference?

 

With 86/87% peaks in duty cycle, your really asking for trouble if you run out of injector and go lean. Start small, and log, watch your DC and watch your narrow band o2's, .880-.890 is 12.8-12.9 on a/f and smaller numbers equal lean and larger numbers equal rich. They are not real accurate once you get away from 14.7:1, so it just something to give an idea. Only you can make the choice if it's ok and far you want to push it. yes the 28's will help, but still only so far.
Robert

 

run a wet shot and forget about swapping injectors.

 

Which brings up a good point, $$ for going wet can be put towards a set of 42's which aren't much-under 200. In my personal web site in the links section is a company that sells injectors for cheap. I have no connection what so ever with them, but they have great pricing.
Robert