Nitrous FAQ


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Page one deals with the basics in nitrous oxide.

Page two deals with all the different stuff and gadgets that goes into this.

Page three deals with common questions and calculations.

Page four deals with installation of a dry single fogger system.

 

To use the nitrous you have to do three things: 1) Open the bottle valve. I usually only turn it off when I'm done driving for the day and when I know I won't be driving for a while (when I'm at work). 2) Arm the system with the switch. I have my switch under the steering wheel. 3) Full throttle! The nitrous is only injected at wide open throttle. You should not engage the nitrous below 2000 rpm because it will give you everything at once! When you engage the nitrous, it takes of like a bullet! You just shift as fast as you can and the bottle will take care of everything else. You should be a little careful if you are not aiming straight ahead. A couple of nights ago I was on the onramp to one of our local highways, 3/4 through the turn (I was doing about 50 mph) I floored it (and thereby engaged the nitrous) and a second later I found myself coming sideways out on the highway :-)

 

The cost of a nitrous system is basically 1) purchase and 2) refill! A basic dry manifold system is about $500, a single fogger wet system is about the same. A port injection wet system is about $200 for the plumbing and $600 for the hardware. A progressive controller is $100-$600. A bottle refill is about $25 ($35 if it's completely empty).

 

Q: How long (total seconds of boost) does it last?

A: 3-5 times/day, 3-10 seconds/hit -> lasts a week with a 70hp jetting.

 

Q: How much does it cost to refill?

A: If it's really empty $35, You should refill it sooner than that since you loose a lot of pressure at the end. Typically $25 for me.

 

Q: Is there different sizes of the nitrous bottles?

A: Standard size (which I have) is 10lb. The thing is that you want to mount it in the length direction of the car, which limit its size. I think I have seen one with a 15lb bottle but that is tight! You can of course mount it left to right in the trunk but that is not an optimum solution when the bottle is getting empty. I think the best solution would be two 10lb bottles side by side mounted lengthwise.

Here are a few of them:

Capacity Length Diameter
5 lb 16.5" 5.25"
10 lb 19" 7"
15 lb 25.5" 7"
20 lb 25.75" 8"

 

Q: What is the kit number?

A: The one I have is kit #05122 from NOS

 

Q: Can the Miata engine handle nitrous without grenading?

A: Don't worry about the bottom end, it's bullet proof! The problems you might experience is that the clutch starts to slip. I have a Centerforce DualFriction and it's holding up fine for 70hp. You might have some problems if you go beyond 100hp as a single unregulated stage and hit it at low rpms. A VERY common misconception about nitrous that I hear all the time is "Oh, you are running nitrous, you will fry your engine!". No, nitrous doesn't burn engine parts, lean mixtures do. That's what fried my spark plug. I knew that I had that problem (#4 running lean), I just hadn't figured out how to fix it.

 

Q: Is the kit CARB certified?

A: No. NOS sells certified kits, but not for the Miata. The only difference between the certified kits and those that are not is that they have spent the money to go through the process for the best selling kits. There is no difference in configuration between the kits.

 

I have had some problems with the nitrous melting my number 4 spark plug. I discussed the problem with NOS and as a first step I moved my nitrous injector further upstream, it's now halfway between the throttle and the airflow meter. It's too early to tell yet, but it looks like the A/F ratio is much more consistent now and it's stronger than ever!

The problem comes from having the injector to close to the throttle, the blast of nitrous is so strong that it shoots it directly to the number 4 intake runner, thereby leaning out no. 4 and making 1, 2 and 3 run rich. This also explains the erratic behavior of the A/F ratio gauge and the cloud of black smoke from the tailpipe that I have experienced when I "hit" the bottle. The final solution will probably be a port injection (one fogger in each intake runner) combined with their new progressive nitrous controller but that will have to wait a while longer.

Most arguments against nitrous are not really valid with modern equipment. After one year of EXTENSIVE use of nitrous I would say that the biggest problems are:

  1. Temperature dependence. The nitrous pressure varies with bottle temperature. Bottle temperature follows the ambient temperature! Of course you can use a bottle heater which will keep your bottle at 84F on cold days, but what about those warm summer days when you realize that your bottle pressure is 1200 psi !! As soon as you hit the throttle, the A/F ratio gauge disappears from the scale, on the lean side :-(
  2. In the long run, it will cost you money! A bottle a week at $15-$20 will, after a couple of years, add up to the cost of a turbo.
  3. You have to refill it! It's a fact of life. If you are lucky (like me), you live 5 minutes from the NOS headquarter :-)

 

If you go for a port injection system, don't aim to low (at least 50hp)! The fuel jets get pretty small on this size of engine and they might clog due to contamination. It does work (you can even have it smaller) but you have to keep it really clean (good fuel filters).

 

  • How to find the right fuel jet

Nitrous jet at 900-925 psi 16 20 22 28 32 36 40 43
Fuel required lb/hr 60-72 92-110 112-135 122-147 151-181 197-236 233-280 246-295
Fuel jet @ psi 4 19-21 26-29 30-32 31-34 34-38 N/A N/A N/A
6 17-19 21-23 21-25 23-26 26-29 30-32 34-38 35-39
8 16-17 19-21 21-23 22-24 24-26 27-31 31-35 32-36
10 14-16 18-20 20-21 21-22 22-25 26-29 28-33 29-34
20 13-14 15-17 17-19 18-19 20-22 22-23 23-26 24-26
30 N/A 14-16 16-17 17-18 18-21 20-22 21-23 22-24
40 N/A 13-15 15-16 16-17 17-19 19-21 21-22 21-22
50 N/A N/A 14-16 15-17 17-18 18-20 20-22 21-22
60 N/A N/A 14-16 14-17 16-17 17-18 19-21 20-22
70 N/A N/A 14-15 14-15 15-17 17-18 18-20 19-21
80 N/A N/A N/A 14-15 15-17 17-18 18-19 18-20
90 N/A N/A N/A N/A 14-16 17-18 18-19 18-20
 

To find the right fuel jet in the table above, find the nitrous jet size you are using in the first row. The second row is primarily for information. Then find the row with the fuel pressure you are using (in the second column), the 3'rd step is to find the intersection and there you have the fuel jet size!

Example:
Lets say that you have a Miata with a single wet fogger and a 36 nitrous jet. Lets also say that you are providing the fuel directly from the fuel rail without any pressure regulator. That means that you are feeding the fogger with about 40-50 psi fuel pressure. Find the column for nitrous jet 36 (3'rd from the right) and find the row for fuel pressure 40 psi (6'th from bottom). The intersection says that you should use a fuel jet of size 19-21. Just remember that these values are a starting point, final tuning have to be done with oxygen sensor, exhaust gas temperature or spark plug reading.

 

  • How to calculate HP from nitrous jetting

The following is intended as a safe baseline for fogger systems using a fuel pressure of 5-6 psi (flowing) and nitrous pressure of 900-950 psi. ignition timing should, as a baseline, be retarded 1.5-2 degrees for every 50 hp worth of nitrous. Fogger2 nozzles may require a smaller fuel jet, however nitrous jets remain the same.

 

Nitrous jet Fuel jet Horse power
(900-950 psi) (Gasoline) HP / CYL HP x 4 HP x 6 HP x 8
14 18 6 24 36 48
16 20 9 36 54 72
18 22 12 48 72 96
20 24 15 60 90 120
22 26 17 78 102 136
24 28 20 80 120 160
26 30 25 100 150 200
28 32 30 120 180 240
30 34 34 136 204 272
32 36 38 152 228 304
34 38 40 160 240 320
36 40 45 180 270 360
40 44 50 200 300 400
42 46 60 240 360 480

 

Fuel pressure regulators should be set to a flowing fuel pressure or false readings may be obtained. To set flowing fuel pressure on the vehicle, use a test jet flowing fuel into a container. To find what size test jet should be used when flowing multi nozzle systems, use the following formula:

Jet sizeČ * number of nozzles (per fuel solenoid). Then take the square root of this number. This is the jet in thousands of an inch.

Example: Eight #32 fuel jets are equal to one 91 jet. 32*32 = 1024*8 jets = 8192. The square root of this number is 90.509

Systems using multiple stages and/or HP levels over 400 hp will benefit from a super Hi-Flo bottle valve and/or a larger bottle due to a lower pressure drop during a run.

 

I should probably mention that I have no interest to any of the companies mentioned on this page, economical or otherwise. I do recommend them since they have all been a pleasure to do business with.

 

Last revised: Friday, February 02, 2007