School me on nitrous dry kits

We rely on the injectors to add fuel in N/A, blown or turbo applications. I don't see why we can't rely on them for small/medium nitrous applications. As long as the amount of nitrous injected doesn't need an amount of fuel that exceeds the injectors, I don't see why the dry kit is a bad approach. (propellerhead)

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I have to agree that definately makes sense! There is also a company called Harris Speedworks that makes nitrous set-ups and seems to have a large following in the F-body world. They make a dry kit with a WOT switch that sprays thru the MAF sensor that appears to be really nice, and its price is stupid like $250.00

Another side topic: Does the 2004 4.6 have a returnless fuel system? I haven't read up on this topic yet but someone told me dry kits are not made for returnless fuel systems

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This is true, thats why a traditional dry kit won't work. If it did this discussion would have ended, at least for me, with wet v/s dry.

Nevermind :edit

propellerhead said:

A traditional dry kit won't work on our 2004s? What's a traditional dry kit?

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From my understanding, traditional dry kits used the Fuel pressure regulator to bump the fuel pressure. With the returnless system you don't have the regulator.

I am also looking into a dry kit once my forged motor is done. I definately dont want to send fuel through the blower. I can do all my own tuning and have a 4 position switch for my tunes, so that isn't a problem. My only question is in regards to spraying before the MAF. I keep seeing conflicting stories on this. I would like to hear from someone that has actually done it, and were there any problems with freezing, or turbulence throwing off the MAF reading. If so could these issues be solved by changing the position of the nozzle. I plan on running only a 50 or 75 shot mainly to cool the intake charge.

Ughh head hurts.
1. Most current Dry kits do spray before the MAF. They do relay on the ECM dumping in the additional Fuel. As far as jetting, most people with dry kits go with between 25-100 with the vast majority I've seen spraying a 75 shot. However with big enough injectors you can spray upto and perhaps over a 300shot. Of course everyday driveable might be a tad bad.

2. I'd suggest a fuel pump upgrade regardless. Injector's if going with a dry kit and spraying a 100 shot I would do also.

3. False. There are lots of people spraying a 150 wet shot with 0 upgrades to the longblock.

As for the entire dry v wet that is your call it's your money. I would suggest a custom dyno tune no matter what kit you go with. I would also suggest starting out at a smaller shot. example you seem to want a 125 shot, I'd start at 75 or 100 jetting. Then as you get used to it increase.
Also most people will suggest a window switch and an on rpm of 3k or greater. I have ran for 2 seasons with 0 issues I never spray below 3k and currently I have mine coming in at 3700rpm.

Now remember on 2004's there is no schrader valve, so if you decide on a wet kit you will need to get a fuel rail adapter.

Jstreet- since you are blown I'd conisder a lower shot to start with. It seems fairly common for a FI car to see double the increase in hp as the shot rating.

Go direct port, or go home.

propellerhead said:

Another side topic: Does the 2004 4.6 have a returnless fuel system? I haven't read up on this topic yet but someone told me dry kits are not made for returnless fuel systems, or something like that.

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A 2004 is returnless, but the only way that would interfere with running a dry setup is if the dry kit were designed to rely on t'ing off a FPR vacuum line in order to provide a vacuum reference when you spray. The less vacuum the greater the load reference and therefore the increase in rail pressure.

Like I said there a bunch of people that have been successfully spraying through the MAF for a long time with no problems. You just need to place the N20 nozzle at least about 6-8" away from the MAF to avoid excessively cooling the MAF sensor elements. I have even worked on a few cars where they actually turned the N20 nozzle to where it sprayed backwards (upstream) away from the MAF. On their particular application it seemed to make the fuel corrections more consistant and there was no change in RWHP on the dyno.

Most of the information I have tried to contribute to this discussion thus far has been based on fact. However, I have a question/idea. Think of the density differnece between air at a high elevation on a hot humid day v/s the air at sea level on a cool non-humid day. If the ECM can correct for such a big difference in air then in theory or at least in my mind it could easily accomodate for a mild shot of N2O (say maybe 50hp) flowing past the MAF sensor. I'd like to see some sort of calculation based on the amount of oxygen at elevation, sea level, and with a mild shot of N2O. I wonder if there really is that much of a difference. I hope what I am trying to say makes sense???

this is why i love my 98. I love my Dry Kit.

I would recommend Zex Anyday!

uhoh5.0 said:

Most of the information I have tried to contribute to this discussion thus far has been based on fact. However, I have a question/idea. Think of the density differnece between air at a high elevation on a hot humid day v/s the air at sea level on a cool non-humid day. If the ECM can correct for such a big difference in air then in theory or at least in my mind it could easily accomodate for a mild shot of N2O (say maybe 50hp) flowing past the MAF sensor. I'd like to see some sort of calculation based on the amount of oxygen at elevation, sea level, and with a mild shot of N2O. I wonder if there really is that much of a difference. I hope what I am trying to say makes sense???

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Yes, you are onto the right track. I have been tuning LT1's, LS1's, and BBC's for a while now, but admittedly I am fairly new to the mod motors and Ford PCM's. But so far from what I can tell, the GM and Ford PCM's are not all that different.

Here is my personal experience so far with these mod motors.

One of the things the PCM does to adjust fueling is calculate how far off current air density is from the VE tables referenced density. To determine the density of the atmospheric air, it is necessary to know is the actual air pressure (absolute pressure), the water vapor pressure, and the temperature. Since our cars don't actually have a baro sensor or MAP sensor, our PCM's don't have a way to finitely determine what altitude we are at nor what the outside absolute barometric pressure is. It has to make an educated guess using known gas constants and data sampled from the MAF and IAT collectively.

Here is something that seems to confuse a lot of people even tuners. A molecule of 100% relatively dry atmospheric air contains more mass than a molecule of pure water. So it is important to consider the individual mass of each of the molecules in the airstream flowing through the MAF. Nitrogen comprises about 78% of the air our motor’s inhaled air, and Oxygen comprises about 21%. Then there is less than 1% of other trace elements. Nitrogen has an approximate atomic weight of 14, so an N2 molecule has a overall weight of 28. Oxygen has an approximate atomic weight of 16, so an O2 molecule has a weight of 32. Then we have a water molecule, or H2O. Hydrogen has an atomic weight of 1. So the molecule H20 has a weight of 18. Notice that a H20 molecule is lighter weight than either a N2 molecule or an O2 molecule. Therefore, when a given volume of air, which contains only a certain number of molecules, contains some relatively light H20 molecules which in turn prove to yield less mass, it will weigh less than the same volume of air without any water molecules.

When humidity increases, and altitude and temperature remain constant, relative air density decreases. Humid air, with a relative humidity of 100%, contains about 0.023 kg of water per cubic meter of atmosphere. That makes up less than 1.9% of the mass passing by the MAF. The MAF doesn't care what is traversing the MAF sensor elements; it can be N2 molecules, O2 molecules, H20 molecules, etc.. It's all mass to the MAF, but the different types of mass effect the MAF sensor element cooling in different ways so that is important to bear in mind. Since the dry air molecules actually contain much more mass like I mentioned above, they have much more of an effect on the cooling effect on the MAF sensor elements than does the humidity (H20) in the air. Neither the MAF sensor nor the PCM know what is cooling the sensor element, they make an assumption based on the voltage required that is sent in return to the MAF to maintain a closely monitored target voltage through the sensor. This assumption is reflected in the Frequency(Hz) to Airflow(g/sec) lookup table. So humidity has the least effect on air density as compared to changes in altitude (Baro) and temperature.

View attachment 416887

Ideal Gas Law - P*V = n*R*T
P = pressure
V = volume
n = number of moles
R = gas constant
T = temperature

Suffice it to say, there are some fairly complex thermodynamic algorithms that go on within our PCM's that most people are completely unaware of. The BARO PID (Parameter Identification Display) and the fuel trims (mainly LTFT’s) are closely related. Humidity has more of an effect on STFT’s.

Another thing about the MAF sensor is that it is not an airflow meter like an anemometer. It is only good at determining changes in mass airflow and it always assumes a laminar flow, that is it assumes that the air that is passing through the sample tube or over the elements is wholly representative of all the air passing through the entire MAF housing. The MAF and PCM are also hardwired to assume that the air flow will be inconsistently unidirectional.

propellerhead said:

I read several FAQs and threads and got a bunch of knowledge. Here's my personal FAQ, as it relates to my 2004 Mustang GT with a fairly stock engine. Please fill in as required.

1. A dry kit sprays N2O before the MAF and relies on the car's EFI system to provide the additional fuel. Depending on the amount of nitrous used, the stock injectors and fuel pump might not be able to provide enough fuel. Hence, dry kits are usually good for 50-125 shots only. True?

2. Anything over a 100 shot in a dry kit will require injector and fuel pump upgrades. True?

3. Anything over a 125 shot in wet or dry will require upgraded pistons and other internals. True?

At this point, I'm leaning towards a dry kit since it has less parts, which means less things to fail (like stuck solenoids), which means a lower risk of kaboom. If #3 above is true then I don't plan on going above a 100 shot so a dry kit makes more sense.

Am I on the right track?

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1. the internals are the weak point going above 125, the fuel system can handle it.

2. see above, i have seen a gt run a 150 shot with a perfect tune. the fuel system can deliver the fuel, but the internals have a hard time.

3. good idea to upgrade for 150+

a wet or dry 100 shot is perfectly fine on a stock engine, get a window switch though. wet kits are safer imo, solenoids have a very little chance of failing, they all have lifetime warranties. on dry kits you can go lean if the nitrous does not hit the maf just right because your fuel system will not compensate for the extra oxygen. wet will make more rwhp as well. the wet-kit is not very hard to install at all, the only problem i ran into was that my 03 did not have a shrader valve.

LaserRed:

So what is your opinion based on your knowledge of the MAF system and the computers ability to adjust to airflow in reference to a dry kit that sprays a small shot (like 50 to 75hp) thru the MAF sensor?

What wrong with just going wet that seems to make our motors run the best. I had a friend with a 100 shot (dry zex kit) race me. I had the 125 wet and we roll raced and did it from a dig and i put it on him real fast in the first 100 feet but then i pulled him slow for the rest of the 1/4. We had the same bolt ons except for gears i had 3:73s and the driver was good also. What makes you want to go dry anyway?

Oh ya nitrous broke his piston
and mine 2
where i live the climate is always dry HOTT HOTT weather its 75 degrees out right now at 12 pm and our altitude is 3400.

uhoh5.0 said:

LaserRed:

So what is your opinion based on your knowledge of the MAF system and the computers ability to adjust to airflow in reference to a dry kit that sprays a small shot (like 50 to 75hp) thru the MAF sensor?

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Something that small I think will be OK. But at first you should closely monitor your a/f ratios. A wideband on a dyno would obviously be the best way, but if you do not have the means to a use a dyno or wideband then at least get it on a scanner or datalogger and go make a couple of spray WOT runs.

When you are relying on the MAF to adjust fueling enrichment for a dry shot, it is best to get the nozzle as far away from the MAF as possible. The reason is you want the N20 and air to mix as throughly as possible as to provide the most consistant temperture drop as possible. If you have a stock type fender airbox, I would really recommend placing the nozzle in the air box behind the filter. That seems to provide the best results and avoids surging due to the inconsistant and uneven cooling of the MAF sensor elements.

Another thing is that the IAT can get cooled too much and apply excessive timing advance and/or excessive fueling variables to several tables used in open loop (WOT). You could relocate the IAT upstream of the N20 nozzle, but much of this can be worked with by way of tuning, but sometimes it can get tricky.

That's why I personally chose to go wet. Both the fuel and N20 are sprayed without going past the MAF or IAT. Even though the problems would be minimized with a 75 dry shot going through the MAF, a wet shot would completely eliminate any doubts as to the MAF and IAT and you tune the fuel with the fuel jet obviously. The wet kits are extremely simple to install as well.

I know there is more of a chance of a nitrous backfire with wet. But if everything is setup properly and you use the system properly, there shouldn't any backfire anyway. But, if by the odd chance there were, I would rather spend 1.5 hrs R&Ring the intake manifold than rebuilding the motor due to an abnormal lean condition.

Go right ahead, spray 150 dry. I will laugh when a rod is sticking out of the pan

LaserRed01GT said:

Why is buying a dry kit a "cheap out"?

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Because you can spend a few hundred dollars more and get a safer kit.

Nitrous Oxide is N2O so be weight it has more oxygen per unit than air. Most wet systems are set up for around a 5:1 ratio.

the98stang said:

Go right ahead, spray 150 dry. I will laugh when a rod is sticking out of the pan

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Honestly, why do you feel the need to make such a uneccassarily immature response?

the98stang said:

Because you can spend a few hundred dollars more and get a safer kit.

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"Safer" is a relative term. Either dry or wet can be setup to be as "safe" as is possible when injecting nitrous oxide into an internal combustion motor.

LaserRed01GT said:

Honestly, why do you feel the need to make such a uneccassarily immature response?



"Safer" is a relative term. Either dry or wet can be setup to be as "safe" as is possible when injecting nitrous oxide into an internal combustion motor.

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How is that an immature response? The engine is BOUND to blow with a shot that big, especially if it's a dry shot (assuming the car has stock rods etc).

It is PROVEN that dry kits aren't as safe as wet kits. Just because it hasn't happened to you or others on the board, doesn't mean the kit is the safest available. I have spoken to many pro racers that use direct port systems, and they all agree that it is the safest kit available, especially when running larger shots.