NITROUS OXIDE ( nos / n2o ) advice forum

Hello

Well I finally got the system installed in the FTO

Did the static tests, a bit rich but all worked ok. However the pressure gauge now showed only 3-400 psi even after 40 mins of having the bottle heater on.

I went to my local filler (Top Gear in Stockport) to get some N2O - he only had about 3 pounds left which he kindly gave me gratis with a promise to call me when more is delivered. So that's nice.

On the way back I decided the sensible thing to do was to give it a shot. The car took off like a scorched rat! Never known anything like it So much so that I got to thinking there was no way that was a 25hp shot, and switched it off.

So today I did some more static testing. It turns out there was no jet in the nitrous pulsoid at all! I changed this one recently as I found the original one I had didn't work - must have failed to swap the jet when I swapped the pulssoid. So must have been as much as the 4mm pipe could handle - I'm told about 75hp?

Anyway, with jets in I proceeded with the test. From 3000rpm start point (as redline is 8k) it would only go to 4500 or so. This was more or less the same changing from a 2:1 to 3:1 ratio. I don't want to go any leaner than that without checking in with you really.

Bottle pressure was down to about 600psi - I presume that could be a factor. I also think my pipes from the pulsoids to the crossfire are probably a bit too long.

I tried it on the road with this set of jets (35hp - n20 jet marked 70 and fuel marked 20) and could feel a difference in acceleration, but fairly subtle to be honest.

My plan therefore is to get a full tank so I have decent pressure, remount the pulsoids and try the static test again. If I get the same results on 3:1 I guess I'll try a road test and inspect the spark plugs - I don't want to lean it out too much. I know not all engines respond the same way to the static tests anyway.

Plan is once I've got the ratio right is to go to 50 - 75hp. I'm using a Minimax too, by the way.

Thanks for reading this far! Thoughts and advice please?

Tim

Get a wideband kit something like the aem uego.i had no luck with the static test on my Bmw so left it at 3:1 and when I fitted the wideband I was running 10:1 AFR so leaned it some more to around 11.5-1 AFR can't remember the exact jet ratio but a wideband is a valuable tool to tune it and to keep and eye on it

The static test will always work when carried out correctly on 99% of cars and is only potentially unreliable on 'some' turbo cars.

You can't achieve consistent results without a fixed (consistent) bottle pressure and for the guidelines & results of a static test to be applicable, the tests MUST be carried out with a FULL bottle at 950 psi.

Using an almost empty bottle and/or a bottle at lower pressure, will NOT produce the same results.

If the pressure is lower the jet ratio required will be different by a proportional amount, so if you are only at 600 psi, the jet ratio will be different by at least 30%, so a 3:1 ratio at 950 psi is going to be at least a 4:1 ratio at 600 psi as a rough guide.

Thanks Trev. Sorry for late reply, just seen this, didn't get the notification email for some reason!

Following on from this, I had a good chat with Lawson in Chesterfield when I went to get my bottle filled. I've progressed on to road testing the setup.

It runs very happily with approx 3:1 but really doesn't seem to like the "safe" recommended 2:1 starting ratio, it just misfires and stumbles.

It does this with a 50 or 75 shot , but not with 25. As soon as I change the jets to a 3:1 ratio (e.g. for a 75 there's a 150 jet in the nitrous pulsoid and a 50 in the fuel) it works fine. Just wanted to check in really, as a mixture too lean could of course have serious consequences. Pulling a plug after a run it looks nice and toasty.

I've tried to make sure everything is tip top as far as possible - changed the fuel filter, fitted a Walbro high flow pump, changed spark plugs, magnecor leads, new earth cables to block and chassis, and changed the oil, brakes and tyres for good measure. I'm running a bottle heater, so nitrous pressure is correct. For the record, I'm using a minimax too.

That all sounds fine, some cars do prefer to run in the 3:1 region and as long as the plugs are checked after the motor is CUT at the end of a decent run, that's the best indicator of a correct mixture.

Thank you Trev, that's reassuring.

I'm putting an AFR meter in shortly too, for good measure