NITROUS OXIDE ( nos / n2o ) advice forum

When I was at the track last and using nitrous everything went good, just my AFR seemed to be a bit high (high 12's) when at the top end of the rev range (between 5,400rpm - 6,2000rpm), mid 11's in the mid range, which is probably no worries as leaner is better at the high end. So I turned up the fuel pressure a bit and the bottle was on 920psi (as opposed to 1050psi when I ran at the track), so it should of put in more fuel, well I think it did but too much. When the nitrous activated the engine cut out within half a second and came to life again (what felt like a splutter was probably no ignition), so I backed off and was puzzled. Would too much fuel blow the spark out or not ignite at all? AFR was in the high 10's when it cut out. Wideband controller may not be calibrated correct either? Fuel pressure = 40psi, bottle = 920psi, jets = 50N-30F (100shot with 4 pulsoids) fuel jetting is high to compensate for hot supercharger intake temps. Cheers

Paul

Hi , Paul , what was the fuel pressure change, also ,are you using a boost type Regulator ?

Could be a spark/timing problem or too much N2O delay, 1.6--1 jet ratio @ 40psi i wouldn't think is not going to flood the engine

As for high intake temps just take some timing out .

Austin

Hey Austin, fuel pressure change was about 3 psi (was set at 37-38psi), I have a 1:1 boost reference fuel regulator.

Nitrous delay is 0.2 secs.

I have a total of 5 degrees retard with a 100 shot, 2 deg when starting at 40% (ramping over 3 secs) and another 3 deg when at 100%. Also the fuel pulsoids put out more fuel than what is set on the progressive, i.e. starting the ramp at 40% is supplying 55% on average, so I may reduce the fuel side of the ramp until it hits 100%.

I'll put up some photos of the data logging.

Paul

First screen, green = RPM, red = AFR, white = fuel ramp (40% start), blue = nitrous ramp (0.2 sec delay). So about 0.2 secs into the nitrous being activated the AFR drops down to about 10:1, then the RPM drops (ignition cut?) until it drops down below 3850rpm which is my nitrous start window, so pulsoids switch off and engine comes back to life again, then fuel starts it's ramp again only to cut out before the nitrous has started.

Second screen, yellow = boost, nitrous pressure = green( which is not reading accurate, the bottle was around 920psi).

Third screen, light yellow = TPS voltage. System activates at 3.5 volts, which shows I had my foot down for the duration of the spluttering.

I think it's an over fueling problem, and that's an easy fix if so.

No I never purged, I was doing this run on the motorway and was in third gear when activated/floored it. low nitrous density and rich fuel would make sense. I should of just left things how they were.lol

Paul

Good to know about not much/if any timing retard needed, should make more power now, I'll reduce it bit by bit though.

Paul

That doesn't look like a mixture issue to me, as it seems to be OK for a short period of time and only starts to become a problem as the nitrous starts to ramp up.

My guess is a spark strength problem.

I have an ICE 7amp ignition module, ICE 16volt ignition booster, ICE coil, magnicore leads (8mm blue one's), autolite plugs heat range equivalent to ngk 8's, cut back ground strap and 0.6mm gap. Never had a problem before but have never checked strength either.

Paul

You can have the best quality products but still suffer problems.

1st of all I'd dump the Autolite plugs and use NGK

I'd then measure the spark strength.

If the spark is exceptionally good 20 mm gap or more, I'd check that the spark doesn't find it easier to leak out of the system than jump the plug gap.

Logs indicate ignition problem as the RPM's drop ,would also check retard function is working ok and not causing a misfire,

Austin

When the RPM's drop the 2nd time around there was only fuel going in as the ramp starts over again, no nitrous at all. I'll get an ignition tester anyway.

Paul

I see the rpm drops below threshold before 0.2 delay times out , if everything tests out ok try without any delay .

At the moment i run a 200hp shot set up as:


1st gear start 45% - 100% build time 0.7 sec
2nd gear start 55% - 100% build time 0.7 sec
3rd gear start 60% - 100% build time 0.5 sec

No N20 delay RPM Window 2100 - 5250

13PSI boost fuel pressure 39.5 + 1-1 on boost

2.2 - 1 jet ratio AFR 10.6 -2* timing at 50%

Just thought i'd share as are set ups are not to dissimilar with the pulsoid to injector pipes so short.

austin

Thanks for that Austin, yeah our set ups are very similar.

10.6 AFR seems quite rich for your 2.2:1 jetting, which probably shows my wideband is not that accurate at all. Time to not be lazy and read the plugs!

I might drop the delay to 0.1sec also, and have the build time a bit shorter, 1 sec perhaps (enough to keep traction). Thanks heaps.

Paul

Retested again on the motorway, 3rd gear, with the following changes. Purged nitrous before activating, lowered nitrous delay to 0.1 second, had the timing retarded to only 1 degree upon activation and a further 1 degree @ 100% (total 2 degrees retard), had the fuel starting at 30% and nitrous at 40% (as the logs will show), and dropped the fuel pressure by 2psi (it was actually set at 43psi originally, now 41psi), Nitrous bottle pressure = 910psi. Nitrogen boost system not on as the bottle is empty, this explains why it's running rich as the push system increases bottle pressure to around 1000psi.
GREEN = RPM
RED = AFR
BLUE = NITROUS RAMP
WHITE = FUEL RAMP
YELLOW = TPS Voltage
The three frames are 2.8 seconds each, total 8.4 secs of data. The 4th photo shows the TPS drops below 3.5volts (which is the nitrous arming window) and is the possible cause of it cutting out, or the shit load of fuel going in, which you can see the AFR dip down to 10:1. Haven't touched the ignition or tested it, but have got NGK B8EFS plugs that I have cut back ready to put in with some new leads for when I go to the track.
Can't explain the lean spike upon activation, maybe the sensor had a tiff like a dyno graph does when the nitrous is activated.
The jump in RPM when the nitrous starts would probably be the the high stall converter flaring up then settling.

Paul

Can't get the 4th photo up as "the board attachment quota has been reached"?

Paul

If photo 3 is TPS related can you lower the activation point or just check it for linear resistance, also just noticed the fuel starts first then lags behind the N2O are they at different pulse % ? , AFR is rich i would jet the fuel down , rather than pressure adjustments .


Austin

Hi Austin, I have lowered the TPS voltage a little, but I just didn't keep my foot down (my subconscience kicked in) as I was approaching traffic. The fuel starts 0.1 secs early, and stays 10% lower than the nitrous through its ramp. When I did the flow tests the fuel pulsoids were providing about 10-15% more flow than the % entered on my progressive controller which is understandable. I will be using the boost system at the track as it is the same bottle pressure all the time so I will tune to that, so the fuel shouldn't be as rich with the extra bottle pressure I'll be using. For the record, it's a US boost system and it has a very slow leak somewhere, hence why I never/or couldn't use it!

Paul

Found that the effect of my pressure drop over the 1/4 shows it richens up by 0.2- 0.3 afr , need to lean it out to between 11.0 - 11.5 AFR to keep top end MPH up ,did some testing last time out but ran out of time before i could run with a leaner setting ,may be one more try before winter sets in.


Austin

When I run the boost system my AFR leans out a bit at the top end so that's good. Hopefully get out to the track in a couple of weeks and crack a 10, otherwise the 200 shot is going in to make sure of it.

Paul

US boost systems are VERY DANGEROUS, especially when used with US bottle valves and you'd be much safer upgrading to our boost system.

The reasons they are very dangerous are;
1) US bottles only rely on a rupture disc (rather than a Safe Pressure Relief Valve) which means there is no pressure limiting system in the nitrous bottle until the pressure reaches excessively high levels.

2) Because of this the nitrous delivery to the engine can reach excessive levels and destroy the engine (as often happens) and worse still it can either reach levels that blow the rupture disc or the absolute worst consequence is that the disc fails to rupture, allowing the pressure to reach levels that can burst the bottle.

The cause of these problems are;

1) The excessively high pressures they use

2) The lack of safe pressure control at the bottle

3) The unreliability of the regulator concept they use

Our systems work at MUCH LOWER pressures, do not use a regulator and our bottle valves have safe pressure control as a secondary back up, plus the boost level is maintained by ACTUAL nitrous bottle pressure.

I might put one of your SPRV's tee'd inline between the boost bottle and Nitrous bottle to keep things safe.
Did an ignition test using the longest ignition wire, approx 35kv on the tester which is about 22mm, before it started to not fire at all.

Paul