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ZEX Nitrous Super SHO's!

Nitrous Oxide:  Down and Dirty in the V8 SHO

In a joint venture with my fellow V8 SHO enthusiast, Scott Waters, we explored the possibility of installing nitrous oxide kits in our 1996 SHO’s.  Inevitably, we purchased and installed 75 HP Zex nitrous systems on our cars.  So far, zero problems with detonation or any other signs of failure.  Scott and I also run with the exhaust disconnected (at the track) which makes for an absolutely thunderous ride.  (If you've never heard an uncorked V8, there's a file posted on my website, listed below.)  The lack of low-end torque from the open exhaust and the new Dunlop 8000's produced only a sparse chirp on launching but there was abundant torque steer. Getting the car to hook up at the drag strip is another story.  Having a free flowing exhaust is important when running a nitrous setup, but if it’s too free flowing, performance can be hurt.  My best time, on street tires, is 14.39 @ 96.87 mph.  I feel that the lack of backpressure from the open exhaust is hurting the car's performance while running nitrous.  I'll be searching for some sort of exhaust setup that will be free flowing, yet provide a slight amount of backpressure.  Scott’s car runs 13.8 @ 102 mph at the track, but then again, he has a UDP and drag slicks.  I’ll be gunning for Scott next year! 
Notice the bright purple bottle.  It's enough to make you giggly inside!!!

The kit comes with everything you need:  the 10 lb. bottle, mounting brackets, braided stainless steel line, Zex's Nitrous Management Unit, 55,65, and 75 HP jets, the remote arming switch, wiring and connectors, vacuum hoses and clamps and all necessary hardware.  You will need to buy about 5' of 3/32" vacuum hose, though.  (The hose supplied is too short to reach the FPR on our cars.)

To answer the question as to whether nitrous setups are dangerous: Yes . . . and No.  Yes, if you don't know what you are doing, or if you are a moron and forget to turn off the electric bottle warmer (from a friend on the Maxima list who knew a person who blew up his trunk because of this.)  No, it's not dangerous if you know how nitrous makes HP and how to apply it.  Research and knowledge is the key to making a modification such as nitrous.  This is what Scott Waters and I did.  We learned about the modification by speaking with others who have installed nitrous (Randy Mercante via Doug Lewis, primarily,) and we took the next step.  From speaking with Randy and Doug, we knew Randy's car was running a dry nitrous setup.  They had already done this up to the 120 - 150 HP level.  A dry setup is one that injects a determined amount of nitrous into the intake tract, before the TB.  A wet system introduces both fuel and nitrous either into the intake tract or into each cylinder directly.  The problem with a wet system is that the mixture can pool and be detonated by the heat INSIDE the intake plenum and not in the cylinder.  This causes the spectacular hood removals that some may have seen.  So, we knew we wanted a dry nitrous system. 

Nitrous:  The Basics

Here’s a little bit on how nitrous works. Nitrous Oxide (N2O) is comprised of two parts nitrogen and one part oxygen; 36% oxygen by weight.  This mixture is much more saturated in oxygen than the air we breathe, which makes it a benefit to use on cars.  Nitrous is very cold and in gas form at room temperature.  Nitrous is injected through the intake into the combustion chamber, (by simple bottle pressure at 900psi.)   During the combustion process in an engine, at about 572 degrees F, nitrous breaks down and releases oxygen.  (An added bonus is that the nitrous is so cold, that it can reduce intake temperatures up to 75 degrees; as we know, cold dense air = better power.)  This extra oxygen creates additional power by allowing more fuel to be burned.  The Nitrogen acts to buffer, or dampen the increased cylinder pressures helping to control the combustion process.  Nitrous isn't the dangerous part of the equation, the added fuel is.  If the added fuel doesn't have the added oxygen to match (i.e., when there is low pressure in the bottle or if the nitrous solenoid fails), the car goes instantly rich which can lead to detonation or worse.  If the fuel pressure isn't increased, then the car is instantly lean.  It's a balancing act.  So, the second component of any nitrous setup is adding the correct amount of fuel in proportion to the nitrous that is injected.  How do we do that without big bucks? 

Here is a good shot from the cabin showing the bottle valve and the Nitrous line running through the trunk floor.  Now all he needs is a back seat companion to turn it on!
Now Randy and Doug went all out by getting a dual mode chip, an MSD ignition setup (to control timing retard) and dual stage, progressive nitrous controller so he wouldn't smoke the tires, a larger fuel pump and injectors, and beefed up the tranny.  I couldn't afford that route and wanted to maintain the drivability of the car while being concerned for the durability of the stock tranny.  We still needed to solve the fuel pressure issue and still address the timing retard issue, which I am just mentioning now.  Timing was easy, since the V8's knock sensors would adjust +/- 2 degrees automatically for lean/rich conditions over stock.  (Timing has to be adjusted 1 to 1.5 degrees for every 50-75 HP of nitrous.)  Without a dual chip and a secondary ignition setup, this would limit our nitrous application to the sub 100 HP level.  That was fine because we felt the tranny would need to be beefed up at that level.    With the car adjusting timing automatically, that issue shortly became moot.  But adding fuel still was still a problem. 

Another concern was the platinum spark plugs.  Without getting too deep into this issue, the plugs have to be switched to the standard copper instead of platinum.    I prescribe to this for two reasons:  First, if a failure were to occur, for whatever reason (most likely an over-rich condition) you WANT a plug to fail.  Why?  Because it is much easier and cheaper to replace than a pistons or rings or something far scarier.  So by making the plug the weak link, your worst nightmare will be that you foul a plug.  Yeah, it's a pain to change the back bank, but it's better than changing a bent rod or piston rings.  So, I thank fellow NESHOC’er Al Primm for guiding me through my plug change.  The second reason you need to switch to copper plugs is that the intense combustion chamber heat can cause the platinum coating to flake off.  That’s a no-no as well.  The stock plug on the V8 SHO is AWSF32P (or PP, P+) for platinum.  The copper plug to use is the standard Ford AWSF22C.  The “22” simply means that the plug has a colder heat range and the “C” is for copper.  The stock gap of .042 to .046 works well.

Note the purple "box" mounted on the driver's side strut tower. This is Zex's unique Nitrous Management Unit.  Bottle pressure is fed into the unit and distributes nitrous to the intake (between the MAF and the TB) and to the FPR.  This is probably the only place you can mount the NMU.  
OK, that's nitrous in a nutshell.  So Scott and I were looking for something that would give us a little kick, not break the bank, have a low probability of failure, and adjust the fuel pressure automatically (which we still haven’t addressed yet.)  I credit Scott with doing the research and finding the right product that fit our needs.  Introduce ZEX Nitrous Systems, a division of Comp Cams . . . 

The system is designed for the import crowd . . . Honda, Toyota, etc. but it seemed that it would adapt remarkably well to our needs.  The kit is self-regulating and adjusts fuel pressure according to bottle pressure.  The system is activated off the TPS, which means there are no throttle switch brackets to rig up.  The Zex Nitrous Management Unit monitors the TPS voltage.  When that voltage increased to 4.6, the car is at WOT and the nitrous is injected.  You want the nitrous to kick in at WOT because that’s when the most fuel is being added.  When you let off the throttle, and the voltage dropped below 4.6, the nitrous was shut off.  A unique part of the system is that the Nitrous Management Unit taps into the FPR by means of vacuum tubes to increase fuel pressure.  The system works off of a manifold in the Nitrous Management Unit and is controlled by metering jets, similar to carburetor jets.  One jet is installed inline with the nozzle that is plumbed into the intake before the TB.  The other jet whose size is in direct correlation to the selected nitrous jet, controls the fuel pressure and is installed inline with the FPR vacuum plumbing.  On the V8 SHO, there is only one FPR on a single fuel rail.  (Note:  The V6 SHO’s have dual rails and two FPR’s, so this kit would probably not work well on the Gen I & II cars.)  The stock FPR has a small vacuum hose that runs between the FPR and the intake manifold.  On a stock system, as added pressure is built within the manifold, pressure is exerted on the FPR's diaphragm to add more fuel.  With the ZEX control unit, a metered amount of nitrous is injected to the FPR to add fuel pressure.

If you look closely you will see the braided stainless steel line that goes into the rubber tube connecting the MAF and the throttle body.  This is the nitrous spray nozzle, containing the nitrous jet.
So briefly, there is a master-arming switch in the cabin that turns the whole system on.  When you romp on the throttle, the unit senses 4.6 volts that is generated at WOT and opens the manifold for the nitrous.  The 10 lb. bottle, mounted in the trunk feeds the nitrous over a braided SS line to the engine bay where the control unit is mounted on the driver's strut tower.  The manifold inside the control unit delivers nitrous to the car's intake manifold and to the FPR.  This gives you the proper nitrous and fuel mixture and you are off to the races.  When you back off the throttle, the voltage drops and the nitrous to the intake and to the FPR are cut.  You look in your rear view mirror at the ponycar 4 to 5 car lengths behind you . . . and you smile . . . “Life is good.”

Frequently Asked Questions about Nitrous:

A quick Q & A about nitrous systems, and the system Scott Waters and I are using (portions thanks to the Zex and NOS websites):

Q:  Is nitrous oxide flammable?

A:  No.  Nitrous by itself is not flammable, but the oxygen present in nitrous will cause combustion to take place more rapidly.

Q:  Will nitrous cause detonation and what kind of gas should I use?

A:  Not directly.  Detonation caused by the lack of fuel (lean) during the combustion process or by using too low of an octane of fuel.  Regular pump fuel is just fine for nitrous systems at this level.  Zex recommends 93 octane while NOS recommends 92.  Using a higher octane decreases the chance of detonation, which may be necessary in higher combustion (race) engines.  

Q:  Where can I get my bottle filled and how much does it cost?

A:  NOS has a toll free number 1-800-99-REFILL, and it gives you the location of the nearest dealer with refilling capabilities.  Nitrous sells anywhere from $2 - $4 per pound.  The standard 10 lb. tank will cost $20 to $40 to fill.

Q:  How do I know how much nitrous is left in a bottle?

A:  The best method is to weigh the bottle to determine how many pounds of nitrous are left.  Both Zex and NOS have bottle gauges that measure bottle pressure and can be mounted on the tank or in the cabin.  Usually, bottle pressure starts to drop with 20% nitrous remaining, and you’ll usually start to feel the car surge.

Q:  How many runs will I get out of a full bottle?

A:  If left open, the nitrous will last about 3 – 3.5 minutes.  At the strip, you’ll only be using the nitrous for less than 15 seconds at a time.  You can expect about 12, ¼ mile runs on a full bottle.

In our opinion, this is a relatively inexpensive and worthwhile modification.  The kit costs about $595 through Zex or $500 through Summit Racing.  It’s is a simple installation if you don’t mind changing the plugs out.  There’s no need for any supporting modifications and will run well on an otherwise stock V8 SHO.

All information, opinions, and recommendations are furnished without any guarantees on the part of the author.  Tampering with or altering any automotive emissions control device is, and modifying an emissions controlled vehicle may be, in violation of United States federal and applicable state regulations.  The author disclaims all liability incurred in connection with the use of the information contained in this article.

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