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Old 05-04-2012, 12:58 AM
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new NOS guy

hey guys im building a 383 stroker, 11:1ish with forged h beam rods forged pistons and a crank rated for 1000hp. dart pro1 heads and a very large cam with full rolling valvetrain. im considering shooting a small shot of nos to it like a 150 or so but i dont know enough about it to do so yet. if i do i will be using the carb plate by NOS. ill be running the msd digital 6al ignition with locked out timing around 32 to 38 depending on what it likes. my guestions are things like how do i tune the shot and what jet to start out with? how much timing to i need to retard it back by when i shoot it and also is 150 to small or big of a shot to run?

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Old 05-04-2012, 09:59 AM
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I would go buy some books from amazon or something like that on nitrous oxide. It would be a shame to ruin such a good motor. I have heard 2* for ever 75hp.

Because nitrous oxide is nothing more than an oxidizer it is important to have a good fuel supply for the fuel circuit. If the nitrous circuit dies it goes crazy rich and runs like crap if the fuel circuit dies....... well thats not so good.

If you didn't know already nitrous oxide is not flamable or explosive at all. Thanks to the wonderful series of fast and furious some people have come to believe that it explodes for some reason....

I would tune for the A/F ratio on the rich side at first to stay safe. Pull the plugs after EVERY run when your first dialing the jets in. Again it would be a shame to ruin the motor over it.

Make sure you purge to a safe location... Not the air cleaner! I have seen some nasty nitrous back fires from improperly purging or not purging at all.....

Its pretty funny to watch a guy blow up a 07 cadillac csv because as he put it " im only spraying 150 I don't need to purge"
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Old 05-04-2012, 10:01 AM
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on the note of safe purging....http://www.youtube.com/watch?v=zNxFIGqJG9c
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Old 05-04-2012, 10:03 AM
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All the instructions you need will come with whatever nitrous kit you order. Nitrous isn't so simple where it's just bolt on and go. It has to be installed and tuned correctly and many factors enter the picture, such as gasoline octane, compression ratio, spark plug heat range, spark timing, additional fuel pump that is dedicated to the nitrous side only, carb tuning and etc. It all plays a role because the margin of error with nitrous is small window. If it's not right it'll turn a $20,000 racing engine into scrap in seconds. The nitrous companies know this, and that is why they provide detailed instructions on how to install it and tune it to the given engine. If your timing system doesn't have a automatic retard to activate when the nitrous is activated you'll want to get one as the spark timing is critical when using nitrous. You can go to NOS website, Holley's web site, Edelbrock, and likely get some info there, but be rest assured, whichever kit you order will tell you all the information you need to know. Back in our drag racing days in the early 90's we started out with a 140 horse kit. It was simple and easy. We later moved up to the super power shot. Then finally up to the big shot system. The big shot could shoot 350 horses. The first kit was very basic on installation and instructions for additional fuel and spark timing was very simple. By the time we got to the Big shot system the thickness of the instruction booklet was considerably thicker as instructions got a lot more detailed. We had to install a secondary for nitrous only electric fuel pump, spark control box, colder plugs and etc.
The instructions will also tell you about how important bottle temp is and how it effects the pressure in the bottle. If the temp is right and the pressure is right it'll work great and you'll love the instant power. However if the temp is up or down and the pressure is increased or lowered it'll run like crap. So as said, you'll get the instructions you need with the kit you get, because the nitrous companies know as mentioned, nitrous isn't as simple as bolt on and go.
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Old 05-04-2012, 10:15 AM
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DV quick question..

Do you set the nitrous system fuel pressure with the solenoid open and the intended jet size installed? I was helping a buddy last summer set his up and I remember reading somewhere online to do it that way so you know you have the exact fuel pressure when under load.... maybe this is only important when using dead head style fp regulators?
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Old 05-04-2012, 02:24 PM
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ya i understand the science of how nitrous works inside a combustion chamber and because of that i get the importance of getting it right. im spending my entire deployment savings on this motor so i really dont want to skatter it at the first push of the go go button. im gona be running a 175 GPH quickfuel fuel pump so flow will not be an issue. im also going to have dual air/fuel ratio gauges hooked up during initial tuning. im just wondering how you go about tuning the fuel to nitrous ratio right off the bat. i defenatly dont just want to guess a jet size and try it with my fingers crossed haha. as for fuel ill be running 96 to 100 depending on what im doing, hell most likely 110 on race days. ill defenatly look into books on nos systems but i want to hear from people with experience.
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Old 05-04-2012, 09:46 PM
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Here's a calculator to find out proper jet sizes to start. Go 1 or 2 sizes larger on fuel to start and pull then back based on plug readings. Be careful with A/F gauges, even a wideband. Location of the O2 sensor can give greatly different readings. Plugs don't lie. Shoot for 11.8:1 to be safe under spray to start.

http://coldfusionnitrous.com/nitrous...alculator.aspx
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Old 05-04-2012, 09:47 PM
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Zild, as far as I remember what you read is correct. I recall on the small 140 horse system we used, all we did was run another line off the mechanical fuel pump to the nitrous solenoid and it worked great. We later got into the experimental stage and added more holes to the spray bars and sure enough it picked up more power when we did. By the time we got to the big shot it had to have it's own dedicated pump on the nitrous side, and I remember having to adjust the fuel pressure on the regulator by watching the guage to keep a eye on the pressure. We would do what I call "dry runs" and leave the plate off the engine and just connect the fuel side on to the plate and make sure the fuel pressure was at it's recommended psi when the nitrous was activated. The fuel pressure will be somewhat different compared to closed solenoid and open solenoid. It seems like in closed position we would set the fuel pressure like a half or 3/4 of a psi over the recommended number so when it was activated it would drop to the recommended pressure, but it's been so long ago it's hard for me to recall it all. Even if the book didn't recommend it it's still a good idea cause I have seen what happens when not enough fuel is added to the nitrous. It goes lean and very bad things happen.
I think if the fuel pressure was a half a psi higher than recommended it would still be okay. On the slightly rich side with nitrous is okay, but nothing on the lean side is good.
I also learned that the health of the ignition system is very very important. Nitrous hits the intake at minus 128 degrees, very cold, so a fat heavy spark is needed to light it off. It''s a simple fact, Nitrous can put you in the winners circle when it's right. Or it can send you home broke and crying with a engine to rebuild when it's wrong.
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Old 05-04-2012, 11:24 PM
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we have my firebird set by the paper chart.52 nos-48 fuel which they say is 125hp, by the site i just went to it said 122fw hp. but on our coupe we ran a 10-12 spread on the nos to fuel ratio! so be careful it wil bite you in the *** quick.
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