I have a mate who has a NOS wet system for his car. To tune for the system, is it just a matter of pulling some timing out of it and leaving fuel alone, as it supplies it's own fuel? He wants a 100 shot, so how much timing should be pulled?

As a rule it is 2 deg for every 50hp. I would get it checked on a dyno to ensure teh AF's are still good. Look for around 12.5:1 under full power, he may need to adjust the fuel or NOS pills either way. Ensure all testing is conducted at the same bottle pressure, aim for 1000PSI as that is the optimum the kits are designed for. Also ensure it is not activated below 2800rpm as this puts undue stress on the internals. Lastly dont use a blow torch to heat the bottle as it can explode, and gives a false high reading due to a spike in the pressure.

Brett

I asked him if he had a bottle blanket. He reckons he was told he didn't need it. Does the bottle need to be heated in some way? He'll be getting it on the dyno, for sure.

100 shot is a descent shot. If it is an old tired motor it will need a fair bit of timing taken out. the 2 deg is the rule but you can usually get away with less than that. Just check for pinging when you are in say 4th gear cruising along and you drop it back a few gears and stand on it, that is when nos will dettinate the most.

The nos will cause extra valve/ cam float to so make sure there are a descant set of valve springs in the head. 90lb crowe or stock XR springs are fine.

It is easier and safer to use the fuel and nos jets that are reccomended and change the fuel ratio in the tune at full throttle.

A bottle blanket is not a must have it will just help your keep a constant bottle pressure. If he is running a zex system with the nmu, bottle pressure is not as bigger deal as with stand alone solanoid dirven systems because the nmu will adjust the fuel pressure to compinsate for the drop in nos pressure. All this means is that as the bottle pressure drops the shot will decrease in size. So if you were to do a 1/4 mile run with no blanket, you would leave the line pushing a 100 shot and probably cross the finish on a 50 shot.

Also unless he is putting a burst plate in the manifold, don't stab the throttle on and off really quickly activating and deactivating the nos. It will more than likely cause a nos backfire which can do some annoing damage to the air intake, manifold, TB etc.

A 100 shot should have a purge fitten to. The addition of air instead of nos into the cylinder can cause serious dettination and leaning out possibly killing the motor!

Good luck

It's an NX kit with the plate between the upper and lower intake. He's definately got better springs than XR springs. The jets that are to be used will be the ones that came with his kit. I don't think we'd have thought to use anything else.

Are the bottle blankets electric? Do they just run off a power supply from the car? I think constant pressure would be ideal.

What's the go with a purge. Do you need a seperate module for this?

Incorrect!!!!

You must ensure the N/A tune is spot on (ie dyno with no NOS) and ensure the A/F ratio is safe at WOT, before you even think about activating the NOS.

Then with the NOS, you need to jet the fuel rich to start off with, and drop jet sizes until its in the ball park (12.5:1)

If you mask a bad nos setup by altering the base n/a tune, then expect fireworks

Yeah, the tune is spot on. Last time on the dyno it was around 12.5 - 12.8:1. Tuning the NOS will be happening on the dyno as well. I think I've talked him into a purge kit and bottle warmer as well. He's hoping to have it all sorted by the drag season, but we'll see.

No what is said is not incorrect! Maybe i should have explained it a bit better, dumbed it down! I said use the recomended jeting which will be extremlly close to spot on then tune from there. I said noting about masking a bad setup with a tune. It is common sence, I would have thought, to have the tune right before even going for a full power run NA.

This is how it was done with my car and every other car that has been tuned by Rob. Changing the jets is time consuming and will not always get you on the money anyway.

I agree if the ratio is way out then they need to be changed but i am yet to see that, if you stick to the suppliers reccomendations for your jet sizing. I have nitrous on my falcon and know the issues that come with it on the car, stick to the reccomendations and you will be fine.

I would disagree with the above.
I run the Edelbrock RPM Plate system and used the jets recommended in the kit for a 75hp hit.
Then i tuned it. The WOT AFR was lower that 10:1. I had to increase the NOS jets several sizes larger, as an .11 is the smallest fuel jet i could get. This is an 8 port direct injection NOS plate that fits between the upper and lower of the RPM II, so i know what you mean by it being a pain to change jets.
Brett

Interesting thread this one.

I'll add my 2c

You do not ever, ever, ever change the tune of the engine to compensate for the tune in the nitrous system.

you get your engine tune spot on and treat the nitrous for what it is, a completely separate system.

if the fueling is not right you can change jets OR fuel pressure OR both to fix the tune.
It requires you to run two separate regulators to make changes with fuel pressure.

You never want to run richer then 12.5 with the nitrous on. You can get incomplete burn and end up with unburned fuel in the ring lands, if this fuel burns there, bad things will happen.
with nitrous to rich can be just as bad as too lean.

In some cases it can be of benefit to decrease the fuel jet size and increase fuel pressure to get the correct flow rate, it can help with atomizing the fuel.

You shouldn't change the gas jet unless you want to change the 'shot' amount. it's size is based on the amount of oxygen contained in the gas and the amount of oxygen you need for a given amount of power.