NITROUS OXIDE ( nos / n2o ) advice forum

I recently got my Impreza mapped on the dyno. I have a single point wet system with the crossfire injector placed in the intercooler 5 or 6 inches from the throttlebody.
Using a 100 nos jet / 40 fuel jet the car runs an AFR of 10.8.1. The car made 501 bhp which is a gain of 60hp on normal, this with the map boost, fuel and ignition trimmed back.
Is the AFR ok or does it seem too rich for nitrous ? I've heard that it's important not to run too lean with nitrous but also a view that AFR should be around 11.7.1 for my type of car.
These are dyno figures and the next step would be to check the AFR out on the road were I suspect it could run a tad leaner.
From where I am placed, to run a leaner mixture would it be safe to gradually increase the nos jet size?
thanks
Trev

You should be able to run a bit leaner but richer is certainly safer and as long as you can get the end result you are looking for, it's only going to cost you a bit more in nitrous and fuel, than if you had it running the leanest AFR it will run at.

The choice is yours, perfect mixture and save a bit of cash or slightly too rich and waste a little cash but avoid the increased risk of having to spend a bunch more on repairing the engine.

To add to The Wizard's comments, you've already made more power than the jetting is rated at. Without leaning out the AFR, you can further increase power by slowly advancing the timing within allowable limits as given by the spark plugs' condition. With 50 bhp jetting, you're detonation threshold should be lowered enough for you to do this and potentially make more power safely.

that's reassuring thanks.
I know one respected mapper who feels too rich, far from being safer can be as bad as too lean, 10.8 would be too rich for a high powered car in his view.
Of course my own mapper is happy with the fueling and I have to say the car has never felt or sounded better when running nos, under full load.

Turbobox is correct on all counts.

There are some people who think excessively rich is as bad as too lean with nitrous as well but I've NEVER seen any indications of that being the case.
In the case of nitrous use it's my belief that the cause of the problem is POOR components and ill informed people GUESSING that the cause of a failure is because it's too rich.
As long as ALL the fuel has been VAPORISED there should NOT be a problem. However, if some of the fuel is NOT vaporised it will actually cause a LEAN condition and THAT is why SOME people incorrectly blame the mixture ratio, rather than the condition of the fuel itself.

What would be the signs that the fuel is not getting vaporized?

In a wet system would this mean fuel puddling at the bottom of the intake manifold?

Yes, it is one sign of poor fuel vaporization. However, there is another state of misdiagnosed leanness from poor atomization where fuel in the combustion chamber remains liquid and unburned, then carried out into the exhaust system where it then burns and the AFR meter reads rich, and this is where these myths stem from. For example, the AFR could read 10.5:1, yet the actual effective AFR in the combustion chamber could be as lean as 14:1. It is vital that not only are your nitrous components are kept clean, but also your fuel injectors, fuel pump, or carburetor components.

The only true indication of engine conditions is reading the spark plugs directly.

The reason I ask is my static test indicates that I am running lean and I am questioning:

a) that the cross fire is not inserted deep enough in the i.d. of the throttle body boot (that it is not atomizing properly)
b) my fuel pressure is lacking or
c) perhaps the volume is not sufficient

I am having a hard time finding exactly what I am looking for (visually) when inspecting spark plugs, as it seems slightly ambiguous when looking for the telltale signs of running lean on nitrous.

1. Is there a good description what to look for that you can recommend, that would help me when inspecting spark plugs for lean running nitrous?

2. Is it easier to inspect plugs for lean nitrous after they have been in service or when they are brand new?

My next step is to replace the spark plugs with one step colder, as I was due for new plugs and was planning to up the nitrous power in the near future; provided that I confirm that the lean nitrous issue has been sorted out.

Thanks!

You're doing the right thing by asking questions! You'll never have anyone here insult or put you down unlike other forums.

What makes you think you are running too lean?

When performing the static test, the engine wants to eagerly rev past the redline.
Here's my conundrum:

My stock fuel pressure regulator is integrated in the fuel filter near the rear of the car, so the fuel pressure is regulated before it hits the fuel rail (which is generally different from the norm). Now my WON system fuel source is tapped in the fuel rail, so in my case the WON fuel solenoid may see a lower fuel pressure at 2000 RPM = static test rpm; than during WOT.

This may be the reason why the static test appears to show a lean condition, which may be totally safe at WOT.

I'm interested in what you guys think.

Regardless of WHERE the fuel pressure regulator is located, the fuel pressure will be the same at the injector. Most cars these days have this style of pressure regulation including my car. Your car may be modulating the amount of power at the pump in order to regulate pressure further for more precise fuel trimming.

What is the max rpm of your engine and what max rpm is it reaching during the test?

Also what jetting are you using again, 50bhp? The more jetting you use, the faster the engine will rev up.

I'm sure we can sort this out; your car may just not respond to the static test well and you may need to go to the road test to verify your jetting.

Interesting. The max rpm is set at 6400 rpm, I stopped the static test ~6100 rpm as it was still rising rapidly and I didn't want to hit redline where the fuel cuts out and chance having a lean backfire. That would be a bad day.

I currently have the 50HP jets until I can confirm the mixture is correct, then I plan on bumping it up to 100HP.

Today I ordered the new spark plugs which you recommended in another thread. After I've installed them I will do a road test, pull the plugs immediately and post up pictures of the results. Hopefully you will be able to decipher what the plugs show as far as my mixture is concerned.

Thanks for the help!

Can you post some pics of the installation please?

What car is it?

What jet NUMBERS do you have fitted?

You should drop down to 25 HP jets to do the static test, as adding more can cause misleading results.