gr8one99SS

iTrader: (4)

whats a good air/fuel ratio on a n/a motor and whats safe for a dry shot? I am being dyno tuned sat. and i dont know much about tuning. thanks

white2001s10

iTrader: (4)

You're not telling us much, like how high your two stage dry is going to go, so I'll give a general answer.

For a stock 300hp motor N/A 13.0 - 13.4 is a good AFR.
For a 400hp - 500hp motor N/A 12.6 - 13.2 is good.

Every motor is a tad bit different, but if it seems to want much richer than this, then look for another cause like excess heat or excess spark advance at WOT.

Running a bottle generally wants at least 1 full ratio richer, and shows torque increases as much as two full ratios richer.

As an example, it you might run a 13.2:1 AFR for N/A,
and then run 11.7 AFR at the lower RPM, and 12.2 at higher RPM. The transition RPM is usually between your torque peak and horsepower peak.

If you're shooting a large dry shot like 200hp, then you might want to go 11.2:1 at low RPM and 11.8:1 at higher RPM.

These are just examples, as every combo is a little different, but these numbers will get you in the ballpark for sure, and give you a guideline to follow.
Your tuner will probably have a good idea about this as well.

RedHardSupra

iTrader: (1)

white, what do you base these numbers on?

white2001s10

iTrader: (4)

I sniff some N2O, then throw the bones out on to the table. If I see the right pattern in the bones, then those are the AFRs I shoot for on my wideband.

My experience is mostly with N/A and dry N2O systems, and those numbers come from a lot of experimentation and observation. As I stated different combinations respond a little different.
I've ran dry systems from 9:1 AFR to 14:1 AFR, and I like to use a lot of test equipment, plus I'm an oldschooler that also watches the plugs.

N20 dry or wet for that matter is a fixed flow into the engine.
As engine speed increases, the amount of N2O delivered per cylinder is less.
Once you pass peak torque, the VE of the engine also decreases.

So you have the % N2O per normal air decreasing, and the total amount of (N2O+normal air) decreasing as well. Burn speeds slow and power output drops, even though horsepower may still be increasing. There's no need to run so rich at those high RPM.

At the lower RPM up to peak torque, the % N2O delivered per cylinder is much higher, and the VE at peak torque is the highest of course. My observation is that the N2O likes to be rich then. It's not a matter of detonation, but it just makes a little more power.

Running very rich well below peak torque is not necessary, but often gives quicker times. A richer tune there will keep the tires hooked better, and keep the plugs cool. I've seen power get applied smoother with the richer tune down low, and without a loss of MPH at the 60 ft mark.
In the case of a 200hp shot, there can be the issue of keeping the tires hooked.

gr8one99SS

iTrader: (4)

thanks white. I have milled heads that sould be about 10.8 to 1 compression and plan on using about 125-150 shot of nitrous. What else do yoy need to know to give me some more of your expertise.