NITROUS OXIDE ( nos / n2o ) advice forum

My mistake I have a #60 nitrous jet.
Ahhhhh Ha that makes a WORLD of difference!!!!!
Making 20 at the engine from 30 HP jet is REASONABLY good and the difference ill be partly due to the dyno, the engine design, etc. and probably partly due to the pressure.

How is it determined that a #60 jet equals 30 hp? Or a #90 jet equals 45 hp? Is there a general formula based on pressure?
I worked out a formula that we drill the jets to, so that the number is double the HP and yes its relative to the pressure being approx. 950 psi. Anything less than that will result in less power from a given jet size.

To do that ten second test would I need to run the engine? Can I test the flow volume on the bench?
Do the test ON THE BIKE (but with the bottle on a set of accurate scales) and through the injectors/nozzles but remove the HT leads from the plugs and spin the engine over THOROUGHLY after the test is done, otherwise it will be KABOOOOM.

I had to refill the bottles three times . But I don't know exact volume.
Just make sure you know the weight before and after the test and we'll do the rest.

I found that I can use zx10 coil over plug arrangement. But the ignition seems ok and responds to timing changes.
DO NOT use coil over type ignition coils as they are GARBAGE. It's not the 'timing' I'm concerned about it's the strength. Can you remind me what brand of parts you have (with pics if possible) right up to and including the plugs, please.

We played with timing and volume.
VOLUME???? What range of timing and what produced best and worst results?

The runs seem to go like this . I did the static test and we got 51hp. Then we leaned it out some and got 53. We richened it up and it went to 50. Then we added timing changes and it went to 52 then we added fuel and played with bottle pressure. All the runs made about the same power. I changed the plugs after the lean run. Tiny black specs of death. So new plugs from then on.
Really it seemed a perfect 20 shot . Everything we did for twenty pulls changed temps and A/F but not the power.
Which tells me there is definitely SOMETHING limiting the power and I suspect its the ignition strength. Did you buy a spark tester from us or do you have one and if so have you tested the strength?

I am a little disappointed in the motor performance. I had 34 hp before the over bore. So I am going to try a different exhaust system next time.
I wouldn't worry about the NA performance when aiming for nitrous performance, can you send me a pic of the exhaust with bore size of that compared to the head size please?

The spark test was over an inch of very blue spark.
That should be plenty and was it repeatedly consistent at that?. Was that measured at the plug cap and did you measure BOTH?

Cr10 e plugs stock gap. I suspect that needs to go tighter.
If nothing else THAT would prove if the problem is ignition related, because if the power increases after the gap has been reduced THE SPARK STRENGTH IS the limiting factor.
The next time you run the bike on the dyno take another set of plugs and regardless of the result using the first set make the switch to an identical set (type, number and gap) and if the results are the same, reduce the gap on the 1st set and refit and retest.

When I went from a 100 to a 110 then 120 fuel jet it would break up when the fuel came in.
That is another indication of the spark strength being a problem.

By bench I mean on the bike with out running the motor.
Fine.

Are the jets the same for fuel and nitrous. I have from 40-230 WON jets.
Yes

For timing changes we added and removed a couple deg along the curve to see if it helped . It lifted the power through the mid range by removing timing. And really did not change much else. NO detonation or preignition that I could detect. But the specs on the lean run may have had a little.
OK and that's another indication that there is a limiting factor as the changes should have affected peak power as well.

All the testing was done without changing the nitrous jet. After the static test the power was 50 everything we did after that made little difference to the power . But changed the air fuel ratio. I had no problems with spark when the fuel settings are correct. Only after going up in fuel jet size or adjusting the pulsoid to make the mixture excessively rich did things change.
Yes I understood that to be the case.

At 8 to 1 it started to miss.
Now I have a number for it and it's SOOOO rich, it's hardly surprising in that case!!!

I really feel the limiting factor is the nitrous jet.
That's EXTREMELY UNLIKELY as it would have to be 30% smaller than it should be (I'd be very surprised to see in a 5% imperfection in size), plus other factors that I've mentioned lean towards ignition and would have nothing to do with the jet size. Do the gap change would prove it conclusively though.


I will change the nitrous jet and do a static test. If the power comes up even a little and we have a steady air fuel ratio . Then I am ready to run. I only need 48 hp. So the next test will be to hold the 50+ hp for ten seconds.
You may well still see more power by doing that but if the limit is spark it will peak out at a lower rpm.

I will take very careful bottle weight measurements and check the plugs between runs.
Wise move.

I think reducing the gap is a good idea. But I really did not have spark problems. I like the idea of starting with the stock gap. Then reducing it IF there is a power drop at top end.
Lack of spark strength does NOT show up as an OBVIOUS problem (it does NOT result in misfires for example), the ONLY way it shows itself is in LESS power than should be expected, that's why it can be a pain to diagnose.

I did test both coils.
Very good and it was AT THE CAPS?

BTW obviously there's no need for different coils IF the spark is adequate.

I do have my doubts about the ignition. Using an a/f ratio is sometimes tricky. A lean misfire will show up as a rich ratio for example. And it was not revving to the top RPM like it does without nitrous. I need to do More testing that for sure.
Agreed and they are ALL signs of weak ignition.

That was a great first dyno session. I will have the results in a week or so and spend time looking at them. I plan to go back in late February.
Sure was and good plan.

My plug wires are built into the coils. So all the test is done by attaching the spark tester to the wire like a plug and cranking the engine.
So you are using STANDARD OEM coils then!!!!! It is HIGHLY UNLIKELY that they will be adequate. The problem with testing the spark is that its down when there is NO ral load on the electrical supply system, plus as rpm rises the available charge time decreases dramatically, so the available spark strength falls.
Based on THIRTY FIVE YEARS OF EXPERIENCE, I'd be VERY SURPRISED if your ignition is not CAUSING YOU AT LEAST A TWENTY PERCENT LOSS of power, so you can look forward to MUCH better results next time out.
I would STRONGLY advise you to replace your existing coils and leads with Andrews or Dyna coils and Taylor spiral wound leads.

After a long talk with my engine guru. It has been determined the coils should be upgraded. The problems I had with E85 and the behavior on the dyno could be spark related.
Since I have changed everything else. Coils are cheap insurance no matter what.

The fun part of all this is learning new things and really learning old thing you take for granted.
EXACTLY what has kept me so INTERESTED for the past 35 years and there's NOTHING taken for granted more, than the ignition system.

Now I need to learn everything about ignition systems.
Yup, been there done that and so I can assure you that you have A LOT of improvements to come from improving the ignition.

So far I have found that even though I have lots of spark voltage I don't have enough spark duration.
Duration and therefore strength FALL as RPM rises, so having 'adequate' spark strength at cranking can only be considered 'a GUIDE' and RESULTS have to be relied on as the ultimate indicator of what is and is not working at full strength.

I think what is happening is my brief spark lights a little bit of the mix. But then the onrush of fuel puts the fire out. If the spark lasted longer more of the mixture would be ignited and that would burn the whole mix. Maybe?
NOPE that's not what happens - THIS is what happens.
The lack of time to charge the coil to full strength (as rpm rises), means there is less and less Voltage available at higher rpm.
Now this isn't such a problem WITHOUT nitrous, as the NA charge density (and therefore cylinder pressure) doesn't reach anywhere near the same levels as they do with nitrous.
However, when you add nitrous you increase the PRE-COMBUSTION PRESSURES and that requires MORE VOLTAGE, rather than DECLINING Voltage that we are stuck with.

The result is as follows;

Pressure rises and reaches peak pressure JUST as the spark is required.

The strength is inadequate so it CAN'T jump the plug gap WHEN INTENDED.

The piston continues to rise and FALL but WITHOUT the spark occurring.

As the piston FALLS so does the pressure in the chamber and at the point where the pressure is lower, than the level where the Voltage IS adequate to jump the plug gap IT DOES and a spark is created and the combustion charge ignited.

UNFORTUNATELY this is FAR TOO LATE and as a consequence power FLAT LINES or at worst FALLS compared to what WOULD be the case if the spark was strong enough to fire at the CORRECT TIME/PRESSURE.

Changing what I have now is going to be the fun part. I HOPE I don't have to replace the whole ignition system. If so I may have to limit the nitrous to the ignition system. At least for a short time.
Just replace the coils and leads with those mentioned in my first post and you'll be AMAZED at the results.

I've even had customer get such HUGE improvements NA, as to think they'd hit the nitrous button.