A/F Ratios

[MacedoMS]

I'm starting to see a trend where folks are popping motors left and right and I decided to add my $.02

Anyone planning to install N20 should purchase the following:

Hobb Switch (Fuel Pressure Cut)
Nitrous Filter
Window Switch
Wideband A/F Meter w/ Data Logging
Fuel Pressure Gauge

Feel free to add something if you'd like...

[MacedoMS]

I forgot to add the rest of my diatribe...

Everyone knows the old proverb, "Lean is Mean, Rich is Right." This is extremely important regarding N20. Anyone running N20 above 12:1 A/F Ratio is simply asking for trouble. We strive for a number in the area of 11:1 to 11.5:1, just to be safe. I have witnessed very large shots running in the neighborhood of 10:1 to 11:1 A/F ratios making HUGE power.

If I've forgotten anything, please feel free to add...

[MacedoMS]

Colder Heat Range Spark Plugs

[srsnow]

Something I would like to add to the warning about being too lean is that as odd as it sounds you can be too rich. In fact in higher horse power applications I've found that more people tend to hurt their engines from being rich than being lean.

This isn't usually a problem until you start dealing with real high compression ratios and a lot of NA horsepower. What tends to happen is someone runs extra fuel pressure and possibly pulls out an extra few degrees of timing to try and be "safe" and hurts a piston and thinks they were lean. Now adds more fuel and hurts more pistons now he can't figure out what is happening.

What starts to happen is the extra fuel can start to collect down in the ring land and once there it mixes with oil and nitrous to create this nasty little cocktail that has a very low detonation threshold. The high heat generated by the high compression can cause this mixture to reach a point where it will ignite and in doing so, depending on how much is there and the piston design can lift the ring land. Once the ring land lifts you can lose oil control leading to detonation which can a lot of times look like a lean condition. The most common place for this to happen is near the intake valve relief where the piston tends to be the thinnest.

Most of the time this is caused be the wrong fuel pressure for a given jet size. Other things that can contribute to this is too much timing retard or insufficient bottle capacity for a given amount of horse power. In my opinion any thing running 250-300hp in a 1/4 mile should be running either a 15lb bottle or two 10lb bottles.

This isn't something you will see in a street car or even a mild racing application but it something that can happen and anyone thinking about spraying a lot of nitrous on a high end engine should be aware of.

This is a very common thing that happens to guys and they are almost always shocked when I tell them that their problem was most likely caused by an overly rich condition. So I figured a topic about A/F ratios was as good a place as any to try and shed some light on this for anyone that has ever wondered if there was a such thing as too rich.

Sorry for the long post

[lxh89]

The ideal Air to Fuel ratio is usually 12.8-13.2:1; however, the ideal nitrous to fuel ratio is around 6:1 with less than a 250hp shot. Therefore, to calculate optimum A/F when on the bottle, do the following (having a dyno sheet handy will greatly assist). I will use my car as a reference for the calculations.

Find Brake HP: RWHP * 1.15 for manuals, RWHP * 1.2 for automatics
308 rwhp * 1.15 = 354BHP

How much nitrous you will spray: 150 shot

Now add Motor BHP + Nitrous BHP: 354 + 150 = 504

Now divide Motor BHP by 504: 354 / 504 = ~70.25%
Now divide N20 BHP by 504: 150 / 504 = ~29.75%

Now take Motor BHP % times Motor A/F Ratio + N20 BHP % times 6:
.7025 * 13 + .2975 * 6 = ~10.92

The ideal A/F for my car is 10.92:1

If you spray above a 250 shot, a N20 : Fuel ratio of 5:1 is recommended. With nitrous shots below 75-100, you can get away with a N20: Fuel ratio of 7:1.

These numbers are a generic way to target A/F so a couple tenths lean or rich won't have a great influence on power production.

Tony

[pdq]

All good points ! I like MacedoMS advice on safety precautions/measures.

I’d like to add : reading your sparkplugs, they tell you what is going on inside that monster you created and plugs don’t lie…..

There seem to be many variables to safely unleashing the hidden powers of nitrous oxide
(fuel, timing, electrical, tuning issues, etc.) . My .02 cents would be to absorb all the knowledge you can about nitrous oxide. The only problem it sometimes seems like a secret society. Yes, you can call many shops and ask questions and most will help but being realistic they have a business to run and sometimes they just aren’t available when you need them. From experience I would suggest this program for nitrous knowledge.
NO…. this is not spam... and … NO… I do not sell or profit from this program.

http://www.pdqmotorsports.com/page/page/3939350.htm

[MacedoMS]

All good points ! I like MacedoMS advice on safety precautions/measures.

I’d like to add : reading your sparkplugs, they tell you what is going on inside that monster you created and plugs don’t lie…..

There seem to be many variables to safely unleashing the hidden powers of nitrous oxide
(fuel, timing, electrical, tuning issues, etc.) . My .02 cents would be to absorb all the knowledge you can about nitrous oxide. The only problem it sometimes seems like a secret society. Yes, you can call many shops and ask questions and most will help but being realistic they have a business to run and sometimes they just aren’t available when you need them. From experience I would suggest this program for nitrous knowledge.
NO…. this is not spam... and … NO… I do not sell or profit from this program.

http://www.pdqmotorsports.com/page/page/3939350.htm

Reading spark plugs is a crucial part of tuning anything... Good point, PDQ! Spark plugs, spark plug gap and the condition of your ignition system play a huge role in longevity of your engine.

[MacedoMS]

Something I would like to add to the warning about being too lean is that as odd as it sounds you can be too rich. In fact in higher horse power applications I've found that more people tend to hurt their engines from being rich than being lean.

This isn't usually a problem until you start dealing with real high compression ratios and a lot of NA horsepower. What tends to happen is someone runs extra fuel pressure and possibly pulls out an extra few degrees of timing to try and be "safe" and hurts a piston and thinks they were lean. Now adds more fuel and hurts more pistons now he can't figure out what is happening.

What starts to happen is the extra fuel can start to collect down in the ring land and once there it mixes with oil and nitrous to create this nasty little cocktail that has a very low detonation threshold. The high heat generated by the high compression can cause this mixture to reach a point where it will ignite and in doing so, depending on how much is there and the piston design can lift the ring land. Once the ring land lifts you can lose oil control leading to detonation which can a lot of times look like a lean condition. The most common place for this to happen is near the intake valve relief where the piston tends to be the thinnest.

Most of the time this is caused be the wrong fuel pressure for a given jet size. Other things that can contribute to this is too much timing retard or insufficient bottle capacity for a given amount of horse power. In my opinion any thing running 250-300hp in a 1/4 mile should be running either a 15lb bottle or two 10lb bottles.

This isn't something you will see in a street car or even a mild racing application but it something that can happen and anyone thinking about spraying a lot of nitrous on a high end engine should be aware of.

This is a very common thing that happens to guys and they are almost always shocked when I tell them that their problem was most likely caused by an overly rich condition. So I figured a topic about A/F ratios was as good a place as any to try and shed some light on this for anyone that has ever wondered if there was a such thing as too rich.

Sorry for the long post

Good Points too, SrSnow! I have witnessed people blowing up airboxes and such because the shot was overly rich on initial hit. I believe a lot of this falls under activating the N20 at an unsafe rpm as well. I would recommend anyone using nitrous to use a window switch and set @ 3,000rpm minimum.