spray questions

[96z28]

I have really been thinkin hard about bang for buck performance and it seems spray is the way to go. I have heard somewhere that dry systems were crap and that I should stay away from them. I have stock internals for now, I will be gettin forgerd sometime in the near futer. I was planning on hiding it where my jack and spare are in the hatch and getting fuel rail covers to try and hide the things that will go into my intake. Does anyone know another way to hide the system. I was also wondering what brand and stystem to get. I am really clueless about spray. I need to know if I need to get different parts such as fuel pumps and whatnot.

[lt1maro]

Well the first thing, you need to take into consideration is the condition of the motor. I dont know how many miles you are working with but conditions such as blow by with nitrous oxide will turn your engine into chicken noddle soup real quick. The maximum that most people suggest on our stock internal motor is a 150 shot. Im sure Injuneerwill chime in soon because his car is freaking sick and i think he knows everything there is to know about f-bodies . But also you have to consider your fuel pump and tuning and reading your spark plugs. If it is used correctly and tuned correctly it can be safe.

[96z28]

How much can I run on foreged internals? Also can you think of anywhere to hide my stuff.

[Injuneer]

Rule of thumb for reliability is not to add more than 50% to the engines HP with nitrous.... a stocker works out to 125-150HP. Build a 500HP stroker, and you can easilly spray 250HP. Build a 700HP engine and spray 350.

This is not to say you can't spray more, I'm sure people are spraying 200HP on stock 100K mile blocks, but the reliability isn't there. I spray 300 on a 500 HP engine, but I have a lot of dyno tuning time, and it requires highly leaded racing fuel.

Wet vs. dry will be the perpetual debate.... but just to clarify one point - dry systems are NOT "crap". I ran the NOS 5176 dry kit on my stock motor for 4 years, my current system is "dry" and the shop that built my engine runs a dry system on their 7.0-second Pro 5.0 Mustang. It's all in the execution.

The big problem with any nitrous system is "distribution"... you need to make sure you get good, equal distribution of the nitrous to each cylinder, and you need to get exactly the correct amount of fuel to match that amount of nitrous. Niether system is "perfect" in accomplishing this.... the direct port type systems come out on top though.

With a wet system using a spray bar, TB plate or similar in the intake, the problem is fuel distribution. The port fuel injection manifold isn't designed to flow liquid like a carb manifold. As a result, at high flows the distribution of fuel can get upset. As velocity increases, it becomes harder for the fuel to "turn the corner" to enter the intake runner, and you may find the more fuel ends up at the back of the manifold, while the nitrous is evenly distributed over the 8 cylinders. This forces you to "jet" (control the ratio of fuel to nitrous) "rich"..... and that means some of your cylinders are running excessively rich, in order to protect the cylinders that aren't getting as much of the fuel. That costs you power.

The direct port system overcomes this by delivering the fuel and nitrous directly to the intake port, and allowing you to individually control the fuel/nitrous mix to each individual cylinder. The part that some people don't like about the direct prot system - you are constantly spraying cold fuel and nitrous into the port, even when the intake valve is closed. The cold fuel can puddle on the back of the closed intake valve.

The dry system overcomes these problems by simply flowing only nitrous through the intake manifold. That means you will generally find a very even distribution of nitrous to the cylinders. The TB plate is the exception in the LT1 intake.... tests I have seen have shown it does an extremely poor job of distributiing the nitrous.

Problem with the dry system is that now you are relying solely on the injectors to deleiver the extra fuel. And, using the stock PCM, there's not much you can do in an LT1 to control this. You can't spray through the MAF - the PCM doesn't respond fast enough, and the specific heat of nitrous is not the same as air, so it throws off the calibration of the MAF (the LS1 appears not to suffer from this problem.... the PCM is much "faster"). So, you end up controlling the flow of fuel through the injectors by increasing the fuel pressure. The NOS 5167 kit applies a pressure signal to the vacuum compensation port on the fuel pressure regulator and, bumps the pressure from the stock 43.5psi to numbers as high as 85-90psi. This increases the fuel flow through the injector in proportion to the square root of the pressure ratio..... so you can flow 50% extra fuel through a stock injector by raising the rail pressure to 87psi. The "problem" is that this is a very crude way to control the fuel flow, since the flow is going to be very sensitive to the exact pressure and the accuracy of the pressure regulator sending the pressure signal. So, again you end up jetting the nitrous for a very rich mixture, to insure you always have a very rich mixture. You also have to change the injectors for a high pressure system, since the stock injectors don't like 90psi.

While I run a "dry" system, I don't use the stock PCM. I have a MoTeC aftermarket ECU that is capable of running one program for non-nitrous operation, and recognizing when nitrous is being sprayed and switching to a custom program recognizing the specific fuel and timing needs of the 300-shot. The computer is also capable of altering the A/F ratio and ignition timing to each cylinder on an individual basis, and capable of adjusting the timing of the injectors. Put in a large injector (64#/HR), run it at an elevated fuel pressure (58psi = 78#/HR) and even putting out 800HP keeps the injector at less than 70% duty cycle, so most of the fuel flow occurs ONLY when the intake valve is open.

In case it hasn't been mentioned, A/F ratio is CRITICAL. Run lean, you detonate, and you crack a piston, burn a hole through the head, break off the ring lands, etc.

A final question - why do you want to hide your nitrous system?

[95z28]

Probabaly so the local ricers dont see it ??

Yet another knowledge filled easy to follow post, i think i learn something every day from this place. who needs school.

[MN6WS6]

Chiming in here...

Injuneer was the main person I went to on all the boards I visit to help me with my nitrous system. He knows more about dry systems than anybody I've talked to, including NOS tech support line. I run a 5176 on my 96 nearly stock LT1, and ran a 12.36 in the 1/4 on true radials, through the mufflers, with a pulley, K&N, and Crane Firewires as my only other mods (if you can even consider that as true "mods").

If you use nitrous, tuning is undoubtedly the most important thing. A properly tuned nitrous system will NOT blow a motor. With the NOS 5176 kit, you don't have to worry about it, it's already done. So the next thing you have to worry about is safety, which in this circumstance is the features that stop nitrous flow if something goes wrong. You absolutely HAVE to change the plugs and regap to .035. You absolutely HAVE to have an MSD 6AL or some other sort of soft touch rev limiter so that if for some reason you do hit the limit on the spray, it will cut ignition and not fuel and save the motor.

Now, with all that said, here's what you really NEED to safely run nitrous:

MSD 6AL (or other soft touch limiting ignition box) with the rev limit set below your ECM limit. Factory is around 5700, so when I was stock programming, I had my limit at 5500. This ensures that the 6AL cuts ignition and not fuel like the stock ECM does. Cut fuel on the nitrous, bye-bye motor.

Window switch. This only allows the nitrous solenoids to activate between preset limitations. On my car when it was on stock programming, I opened the window at 3000 and closed it at 5300, 200 below my MSD limit. This way, even if I did hit the limiter, the nitrous was off long before that happened.

Fuel pressure safety switch. I believe the 5176 comes with this, but it's been a long time since I checked. If not, you need it. This only allows the nitrous to flow if the pressure is above the set minimum. On the 5176 kit, you only want the nitrous to be able to spray above about 75 PSI (which is roughly where I have mine set). If for some reason the secondary fuel pump does not increase the pressure to 85-90 PSI, this switch will not allow the nitrous to flow. If you flow nitrous at stock pressure, see-ya, cause it's way too lean and it will burn up.

Taking everything into consideration, this is how my system works. #1, the arm switch has to be on. #2, you have to be at WOT (5176 kit comes with a WOT switch). #3, you have to be between 3000 and 5300 RPM. #4, you have to have sufficient fuel pressure. ONLY THEN will the nitrous come through the solenoid and to the motor. The way I have my system would be comparable to having 4 firewalls on your computer. Very slim chance anything's gonna sneak through that many safety nets.

Now, I know that all sounds like a lot of stuff, and in reality, you would probably be looking in the 800-1000 dollar range to equip your car with all the stuff mentioned. But if you do, you will have a safe system. I have run my system on my car for nearly 4 years, and have not had a single problem with it. I put down 370 RWHP and 454 RWTQ setup like that. That's all on stock ECM programming too.

[MN6WS6]

One more thing, I hid my whole system too. Why did I do it? So when somebody see's my car with the hood open they'd never know that it has "the beast in the bottle" installed.

[Injuneer]

I guess mine isn't really all that "visible".... when you pop the hood, the only thing you can see without looking down into the bowels of the drivers fender are the two hoses going to the Ram Air box......

[lt1maro]

I guess mine isn't really all that "visible".... when you pop the hood, the only thing you can see without looking down into the bowels of the drivers fender are the two hoses going to the Ram Air box......

Is there anyway you can put those hoses coming from underneath the intake elbow so it would not be visible at the top.

[MN6WS6]

I have a single nozzle on my dry setup (because I'm not running near as much nitrous as Injuneer is) and mine is below the intake rubber. You would never know it's there unless you were familiar with the LT1 engine. It's covered in split loom so it matches the rest of the wiring.

[Injuneer]

The dry kit is easy to hide. Some people have run the line up through the air silencer tube in the inlet elbow/bellows, and mounted the spray nozzle in there. In my original 5176 install, the nozzle was on the drivers side of the bellows, about 45deg down from horizontal, so it wasn't real obvious..... but I never had any interest in hiding the system. You can see the solenoids and the line running to the elbow in this OLD photo, but you can't see the nozzle.

[MN6WS6]

I forgot to metion I mounted my solenoids down on the backside of the radiator. You can't see them from the top side, you have to get under the car to find them.