When you're at WOT doesn't the computer just got into PE / open loop mode, so the MAF isn't used?

 

Yes, the maf is used in openloop. The pcm just does not use the O2 and calculated fuel trims, instead uses the PE muliplier to richen the afr from the 14.7 that the maf alone should give.
Yes, the maf does indeed register the extra O2 from the nitrous. If you dont think it does.. please, by all means, go ahead and spray a 100 dry after you meter then come back and tell us how it did.
When used properly, with the right fueling and timing, a dry shot is perfectly fine. Nitrous use of any kind will shorten the longetivity of the load bearing parts of your motor but so will forced induction, heads, cams or any thing that increases power output over stock ratings. With that said, I have been spraying my truck with a 100 dry shot for ~50K before I pulled my heads recently at ~100K. The motor was beautiful on the inside. It was a lot cleaner than alot of non-spraying motors that had a lot less miles on it that I have seen. I even still had very visiable cross-hatching in the cylinder walls. So, I will continue to spray my dry shot.

 

With any boosted motor, blower or nitrous, changing you engine lube more often (every 2500 miles or so) is wise as well as the oil gets dirty a bit sooner and breaks down quirker too and normal change intervals may lead to shorter engine life. Also a aux engine oil cooler is a very smart move for any boosted engine too. YOur biggest danger with a 75 or so dry shot is not the wear from boost but the possible melt down from detenation as that boost leve will not have much effect on engine life at all as long as it does not lean out anyway. .

 

Hey BigKID, I was wondering if you had any pics. of how your dry shot was setup. I would like to know how I should set mine up so I can spray before the MAF. Cause I would rather do it the safe way like you.
Did you leave the whole intake on there an just place the N20 nozzle infront of the MAF?

 

Put the jet at the end of the filter if you have a cone... hopefully it's 8"+ away.... or put a jet or two on the side of the air box after the filter.

spray dry shots before the Maf ALWAYS... Some people have even relocate their mafs further away from the nozzle, closer to the throttle bodies.

Do more research before you buy a kit.... I have been looking into a NOS setup for awhile now and I am going with a 100-125 dry shot... I know pretty much what I want to do.. but I still have some debates.. so I am still researching more and making the BEST decision.

take some advise on this because if you make the wrong decision, nitrous is no joke to your engine, and you can seriously mess **** up.

 

I 125 hp dry is playing with fire. At that level you can easily lean out and toast your engine in a heartbeat.

 

Thats why you get scan software to make sure you arnt lean. There are also kits that connect to your 02s and will shut off the nitrious in a lean condition

 

How far does the N20 nozzile need to be from the MAF? Does it really matter?
An if detenation is occuring, could I hear it or feel it?

 

i think some were experiencing a slight freezing of the screen when it was to close to the maf. as far as detonation. there will always be some you cant hear. i am running a 150 shot. i keep tabs on my fuel and kr. the tranny will go first. just be cool with it and you will be ok.

 

Some basic info on nitrous....

Wet = nitrous+fuel introduced after any air metering devise such as a MAF via nozzles or spray bars.

Dry = nitrous introduced without fuel.

Dry nitrous CAN be introduced before or after the air meter (MAF) so long as the system is designed to function that way.

Dry nitrous before the MAF. In this case the nitrous is injected in a fashion such that the MAF is use to determine proper fueling. (see below for basic explanation of how a MAF works) The MAF reads the change in intake charge temp. It uses that data to determin changes in air desity and thus changes in combustable air. Lower temp = more density = more air = more fuel.

Dry nitrous after the MAF. In this case the nitrous is injected in a manor that does not require the air meter to compensate. In most cases, engine vaccum or tps is used to actuate a fuel boosting system. On a bypassing fuel system the vacuum circuit is usually controlling the fuel pressure regulator and under WOT boosts fuel pressure to a determined value to match nitrous flow. Some systems use tps and o2 readings to activate higher injector cycle time. In either case the injectors are directly influenced into flowing more fuel outside of the air meter's reading.

MAF location

I tend to get my best result wit about 8-12 inches of space between the MAF and fanspray. Distance will not be same in all applications as diameter of the intake and number of bends and fanspray location do play a role.

How much dry nitrous is too much?

Depends on your particular set-up .. many variables to consider ranging from state of motor build to converter size to fuel system stability. I have run 175 HP dry without any failure but watching fuel showed a noticable change in pressure (3-5 psi) and i had to let out.

Just some info ...

How a MAF works
The MAF consists of a heated element and it uses a constant to determine airflow relatie to voltage change. As more air travels across it the element cools and a change in voltage is registered the amount of energy require to heat or reheat the element. The amount of air passing over this element and how much it cools the element is directly corolated to the total air volume taken in. In the case of nitrous use the super cool -273* discharge will cool the element and so much that the MAF adds adequate fueling to support the nitrous being injected.

Richard