924Board.org

[Khal]

Pardon my ignorance, what's the difference between a "wet" or "dry" system? (just in layman's terms, not the actual difference in hooking either up to a 924)

Is it just the NOS being fed in as either a liquid or gas?
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'80 924 Turbo

[Paul]

IIRC, dry uses just NOS, wet uses NOS and additional fuel.
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[CBass]

[numbbers]

So, why not just add another cold start valve (injector) to the other end of the intake manifold. Just a simple drill and tap. Using two should provide plenty of fuel, and spread it fairly evenly.
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1980 924 Turbo

[My924gtc]

[plyhammer]

I am ready and willing to try this idea out but I need to find a cheap enough/used kit. Will keep everyone posted if I try it.

[plyhammer]

I have a nitrous oxide systems NOS drykit. I am ready to do the work. I will need some help in how to install this. I mean that I can install the kit, not that tough, but how to do it without the engine running lean? T into the fuel line (but where at) and how do I get the correct spray from the fuel and the nitrous selenoid? What ratio of jets should I use for each. It is a 79 NA I believe at it's best rated at 110 hp. The engine is in good shape and I am willing to document the entire thing with video. I just need the help in getting it in correctly. Like I said, I will be the guinea pig! If she blows, I guess I do an engine swap??? thanks

[CBass]

That's quite a lot of questions. Since you have a '79, you shouldn't have an O2 sensor, so it's not going to correct at all when you're on the juice.

You need a fuel solenoid, so that when you activate the system it will inject extra fuel. Then you'll need to rig up an injector, you can use a cold start injector, as long as you work out some way to control how much fuel is being injected and match it to how much nitrous is being injected. The easiest way to do this would be to buy the correct jets from Holley and plumb them into the hose that feeds your additional fuel injector. You'll have to place it upstream of the throttle body if you want to get equal distribution of fuel to all 4 cylinders.

You can cut the fuel line that goes to the cold start injector, put a tee in and plumb it with rubber hose easily enough. Just make sure you use a tubing cutter, and clean up the ends of the hard tubing REALLY well, you do not want loose metal particles in there.

You would REALLY be better off simply buying a Zex wet kit, as it's the easiest to implement. It comes with everything you need, and isn't that expensive.
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'81 931 in various states of assembly

[geddes66]

Go with a WET kit. Dry kits have to run lean at least long enough to get to the O2 sensor (I know, thats not long) and depend on the original fuel system to add the extra fuel. Do you KNOW that the CIS can send THAT MUCH extra fuel with only the O2 sensors input and NO movment from the air plate? Are you willing to bet yor engine on it?

Actually I don't think yours has an O2 sensor,being a '79, in which case dry N2O is out of the question.

My .02... go wet with a fogger nozzle just inside of the throttle plates. Buy a fuel cell, (so you don't have to touch your CIS) a 6PSI fuel pump and a solenoid. Run race gas in the fuel cell for the N2O. These things shouldn't cost too much and will safeguard your investment.

Leaning out = violent (engine) death with nitrous.

If you are REALLY experimental and cheap (Hey, I am too) set it up such that the nitrous sprays up directly aganist the Air plate, pushing it up and enriching your mix beyond what the somple airflow would dictate. Note: This is grossly inacurate and only good untill the engine would normally be using that much air at the normal 19% O2, not the 33% O2 the nitrous delivers. Then you will, once again, start to lean out.

Go wet.
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The Porsche is now my son's, my car is cooler, slower but cooler.

[CBass]

'79 has no O2 sensor. Dry kit is only an option if you can work out a way of accurately adding the additional fuel required. Not to say that it can't be done, there's just some trial and error involved.

Wet kit is the best way to go. Some of the kits are designed to work with a throttle position sensor, which the 924 doesn't have, but I think you could change the wiring so it activates with a WOT switch, which the 924 does have.

Feeding it with a seperate fuel system is a good way to go, but for a mild shot on a 924, I don't think it's really necessary. When I was looking at using nitrous on my 924, this is the system I devised, but I decided against nitrous in the first place.
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'81 931 in various states of assembly

[plyhammer]

Ok I t up the cold start injector line, run a 6 psi fuel pump to a fuel selenoid???? from the selenoid to mate up with the n2o just as it is entering where a normal n2o kit goes? I use the nitrous calculators that are on line to jet the n2o and the fuel pressures to attain around 30 extra horses and go from there? sound right? I am only confused right now on the fuel pump to the fuel selenoid. thanks

[geddes66]

That sounds right. You could go with a regulator and hook to your existing FI to feed the new sol. but not worth it in IMO. Keep us posted on how it goes.

Upon re-reading your last post, I am not sure what you mean by

"OK I t up"

Your new fuel sonenoid will need PSI just run a line to the pump then a line to the solenoid. Make an "arming" switch that turns on the fuel pump and a "GO" switch (usually a microswitch and relay set for Wide Open Throttle) to open the solenoids
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The Porsche is now my son's, my car is cooler, slower but cooler.