Wet VS Dry for EFI Applications

Wet VS Dry for EFI Applications

This tech article is intended for educational purposes only. My intentions in this tech article are to help you get factual information that is not based off someone’s opinions or what they prefer to use. After reading this article you should be able to make educated decisions to what best fits your needs.

What is a Dry Nitrous System?

A dry Nitrous System is a nitrous system that adds the fuel separate from the nitrous. The Nitrous will be discharged usually at the throttle body or mass air meter. The extra needed fuel will be delivered through the fuel injectors. There are a few different ways this is done.

FMU- Some applications such as a Chevy LT1 or Mustang Fox Body vehicles require a FMU. (Fuel Management Unit). This type of system works by spiking the fuel pressure regulator forcing more fuel pressure to the injectors. The Nitrous Discharge will be placed before the throttle body after the mass air meter.

Pre Mass Air meter- Some applications such as GM LSX based vehicles add the extra fuel through the injectors from a signal that is sent from the mass air meter to the PCM. The Nitrous discharge nozzle is placed before the mass air meter.

Tuning Devices- There are several different tuning devices on the market for changing the fuel tables to the PCM. 

Programmers- On some late model Ford applications you can run programmers that let you run seperate tunes. You can program a nitrous tune so that the computer adds X amount of fuel during set RPMS. 

Tuning software- For the LSX based applications there is tuning software such as LS1 edit, HP Tuners, or EFI Live. This software lets you change the actual PCM tune.

Piggy Back Programmers- Piggy back tuners splice into the system and alter the signal to the PCM tricking it into seeing a different reading than what is actually there.

Pro VS Con for dry systems


  • Bottle Pressure- Bottle pressure is not as critical on dry applications that are pre mass air meter or using a FMU. Since a dry system of this type adds the fuel by the amount of nitrous flow the mass air meter or FMU reads you will not loose any over all horse power due to the car bogging from the fuel still being delivered at max flowing fuel pressure. Low bottle pressure will result in not making all the potential horsepower nitrous creates. ( Excludes dry systems using piggy back tuners or programmers adding the fuel by tuning)
  • Less fuel vapors in intake plenum- Dry applications do not add extra fuel vapors into the intake plenum. Therefore in the event there is a nitrous backfire they are usually less violent.
  • No Purge- Dry applications that are pre mass air meter or using a FMU using a purge is not as critical. Not using a purge will decrease the potential 60 ft times due to the delay in the hit however the car will not add the extra needed fuel into it sees the nitrous. ( Excludes dry systems using piggy back tuners or programmers adding the fuel by tuning)
  • Even fuel delivery- As long as the injectors are in great shape and not over worked you have a better chance of getting a more even fuel distribution to each cylinder. (This does not mean the nitrous will be evenly distributed!)
  • No Fuel Solenoid- Since you are not using a fuel solenoid to add fuel there is no need to worry about the fuel plunger swelling due to methanol in the gas.


  • Tuning Hassle- Dry nitrous systems usually require a little more skill to tune and can be temperamental and problematic during tuning. Due to this reason not everyone can tune is a dry system properly.
  • Added Cost- Most of the time dry nitrous systems do not cost any less than running a wet nitrous system. In some cases they may actually cost more. Since you are relying on the fuel injectors to deliver the extra needed fuel you may need to upgrade to higher flowing injectors. You may also need tuning software to adjust the air fuel.
  • Electrical component failure- With a dry nitrous system you are relying on the mass air meter to deliver the signal to the PCM to add the extra needed fuel. With a piggy back tuner you are relying on the device to alter the signal. If any of these electronic devices fail your car will go lean possibly leading to engine failure. Mass air meter failure is not real common; however it is possible and has been known to happen.
  • Tuning by Nozzle placement- With a dry nitrous system tuning by nozzle placement can be quite risky. In the event that the nozzle where to work loose and change the direction of its flow path the tune would go lean possibly causing engine failure.
  • Fuel injector failure- With a dry nitrous system you are relying on the fuel injectors to deliver the fuel evenly. It is important that the fuel injectors are in good shape. You want to verify that the duty cycle is not above 85 percent, clogged from being dirty, or warn from use. If any of these items are a possibility there is a chance of uneven flow distribution to each cylinder or fuel injector failure.
  • Limited applications- With a dry nitrous system there is not a system available for all applications. Some vehicles will not operate properly with a dry system.
  • Fuel supply- With a Dry nitrous system you are limited to only being able to deliver the fuel from the same fuel feed supplying the engine. Up to a certain horse power level this is not an issue. However you may reach the point the stock style fuel system can no longer support the demand.

What is a wet Nitrous System?

A wet Nitrous System is a system that adds the fuel mixed with the nitrous. This discharge is usually injected into the motor at the same point of entry. On non direct port applications this discharge will be released at the throttle body. On some applications there will be a plate between the upper and lower intake plenum. For the most part all wet nitrous systems are fairly easy to tune.

Pro VS Con for wet systems


  • Ease of tuning- With a wet nitrous system tuning is much easier. To adjust air fuel all you need to do is change out the fuel jet.
  • Less add on cost- With a wet nitrous system since you are not relying on the fuel injectors to add the extra needed fuel. No need to upgrade injectors as long as you have enough injector to support the motor NA. Since you are adjusting the air fuel with the fuel jet you will not need any extra add on tuning devices or software other than to adjust timing if needed.
  • Less component failure- With a wet nitrous system no needs to worry about fuel injector, mass air meter, or software failure.
  • Wide range of applications- With a wet nitrous system there is a system for every application.
  • Fuel supply- With a wet nitrous system if you reach the horse power point that the factory style fuel system can no longer support you can run a dedicated fuel system to deliver the extra needed fuel. With A dedicated fuel system you have the ability to run a high octane race gas in the dedicated tank and regular pump gas in the stock fuel tank.


  • Bottle Pressure- On a wet nitrous system bottle pressure is critical. Your tune is based off of bottle pressure and fuel pressure. In the event your bottle pressure is low it will change the tune up causing a rich condition. When the car goes rich it will bog causing horsepower lost. For this reason a bottle heater is more critical.
  • Fuel vapors in the intake- With a wet nitrous system since you are spraying the fuel into the intake plenum mixed with the nitrous discharge there are more fuel vapors than usual. In the event of a nitrous back fire these fuel vapors will ignite causing the back fire to be more violent than normal.
  • Purge- With a wet nitrous system a purge is more critical. A purge system will greatly increase 60 ft times due to a sudden hit off the line. With out a purge system the air in the main feed line will cause a delay in the nitrous reaching the discharge. Since the fuel will reach the discharge sooner the car to go rich and bog until the nitrous reaches the discharge.
  • Fuel delivery- Wet nitrous systems that discharge at the front of the intake plenum can experience lean conditions to certain cylinders when the point of flow restriction occurs. Knowing the flow limitations of your intake is advisable. When reaching the point of going past manufacture suggested horsepower levels reading spark plugs is a must.
  • Fuel solenoid Failure- With a wet nitrous system in the event the fuel solenoid where to fail it would create a lean condition possibly causing engine failure. Solenoid failure can be caused by methanol cut fuel. Most solenoid manufactures are now using a piston material with a higher tolerance rate. Installing a lean cut off switch can help eliminate engine failure by turning off the nitrous system in the event the fuel solenoid where to fail. Fuel solenoid failure is not real common; however it is possible and has been known to happen.

Is wet or dry the safest?
One of the most common asked questions is what is the safest system between wet and dry. You will here a lot of misleading info while searching for knowledge. Many will argue that one is safer than the other. The truth is both have there liabilities. There is no safest system as far as wet or dry. Adding nitrous to your car is a risk. Wet or dry if the system is installed improperly; tuned improperly or used improperly the ending result will be the same for both style systems. 

Knowing what is right for you.
Knowing which system best fits your needs and capabilities is a must when choosing what is best for your application. I highly suggest asking your self what tuning resources you have around you, what are your tuning capabilities, what are your limitations, what are your future plans and what is in your budget.

Doing it right the first time
If you can not afford to do it right odds are you can not afford to replace the engine. Save up and buy your parts as you get the money. Do not cut corners and think that you are an exception to what is suggested. Once you get all the parts suggested and have the money or ability to tune then install the system. Knowing what you need is what the manufactures tech department is for.

Correct advice.
Getting advice from your friends and internet forums will not always yield the best advice. Know one knows better than the manufacture regardless of how big of a know it all your best buddy is. If you are uncertain of an answer you receive get a second opinion. Even some manufactures tech departments do not always give the best advice. 

I hope that after reading this most of your answers in regards to Wet VS Dry nitrous systems on EFI applications have been answered. If there is something that was missed please give our tech department a call at 254-848-4300.

Don’t forget to have fun along the way.
Nitro Dave