I know with superchargers compression ratio is a huge factor. But is it the same with nitrous? like i mean, if i was to use a 100-150 shot, what is a safe range that my compression can be without causing knocking. Also, i know with nitrous you should be using forged pistons, but what else would be needed to see thtat i dont completlt **** over my engine, and if an engine is build properly for a nitrous operation, after how many usages should it be rebuilt? thankyou, im kinda new witht hte idea of nitrous, so anyadvice would be helpful

 

If you want the motor to last, it will indeed be necessary to make sure the compression is not too high. What is the magic number? Well, depending on the amount of nitrous the more you intend to blast the motor with the lower you will need to keep the compression. With a 150 shot I would guess (note the word "guess" meaning I am not positive) you would probably be safe with stock compression ratios and limited use of the laughing gas.

Nitrous will actually decrease the intake charge's temperature. It is not a combustable gas like many people think. When decreasing the temp of air, density will increase, thus the volumetric efficency is raised. So when you have this increase in efficency the combustion pressure will be raised, therefore you will have to lower the compression in order to keep the fuel from spontaniously combusting in these highly increased cylinder pressures.

I would say around 9:1 compression with a 100 hp shot of Nitrous would be plenty safe.

 

I know guys running 11.1 on a 100 shot. A 150 is going to need more timing taken out of it, obviously.

I sprayed 75 shot w/ platinum plug and 10* initial timing w/ no problems. I went w/ colder plugs and back the timing off to 6 and spray 100 on a regular basis. When I upgrade the pump it'll go up to 150. It depends a lot on how your timing curve is.

 

oops, I forgot, I got 10:1 comp.

 

The most crucial part to a reliable N2O system is the proper use of a wet shot.

Allow me to explain, detonation is the condition of an explosion not caused by the spark plug. It can be too early or a condition when the explosion starts in two different places. This happens when the intake charge gets too hot. It gets too hot from too much oxygen or too much compression.

You see, too much compression simply heats up gas because of the nature of a gas. A gas is a bunch of molecules, and if you force them closer together, them collide more frequently, thus heating up. This is the most common form of detonation caused by supercharging and turbocharging.

On the other hand, oxygen burns hotter than gasoline, so when the mix is heavy on the oxygen side (i.e. lean), it burns too hot. This is the detonation caused by N2O. N2O is a molecule with two nitrogen atoms and one oxygen, although it is not intuitive, this molecule has more oxygen than atmoshere in a given volume. This means a shot of N2O is like a breath of high octane air into your intake. This means you have more air, but to prevent going lean you must add more fuel to match, this is a wet system. The other type of N2O system in a dry system, which is just N2O and you have to try to guess at the right amount of fuel through carb tuning, or bigger injectors. The problem with this is, if you get the right mix when you're on the juice, you'll run rich when you're not and vice versa. A wet shot only adds more fuel when you need it and just the right amount for a given shot. If you ask me, a wet shot is the only way to fly.

So you see, if you use a wet shot, and tune your timing carefully (start with a lot of retard), you should be fine with a 150 shot and 10:1 compression. Look at the hard core N2O guy's on this site, many of them run lots more compression and lots more N2O than you're talking about.

 

Wow, can’t leave this one alone…

Detonation is just when you have 2 flame fronts running into each other. What caused the initial ignition is not really important. A hot spot or source of ignition other then the spark plug causes preignition, which may or may not lead to detonation.

Oxygen doesn’t burn hotter then gasoline, oxygen doesn’t burn period, it’s an oxidizer, fuels burn. During combustion the fuel ignites, burns/mixes with the oxidizer to produce the combustion by products. In a perfect world you’d have hydrocarbons + oxygen going in, and CO2, H2O and energy/heat coming out.

N2O adds oxygen to the chamber, so you can add more fuel to be oxidized by the oxygen (If you don’t the process will look for an alternative fuel, and since aluminum is flammable, usually that is the next thing to go which is how you get holes in pistons when you go lean on N2O).

Wet shot – fuel is added with the N2O through the same nozzle, plate…
Dry shot – fuel is added through the existing injectors… usually by causing an instantaneous pressure rise in the fuel system or if the ECM can detect when the N2O is turned on it can be programmed to add the extra fuel. There is no compromise here.

In both cases A/F off the spray depends on your engine tuning, and in both cases A/F on the spray depends on your N2O system tuning, they are independent of each other. Both only add fuel when you need it.

The disadvantage with a wet shot is that you may not get an even distribution of N2O and fuel in all the cylinders since FI manifolds weren’t designed to flow anything but air. The disadvantage with a dry shot is that you’re guaranteed a good fuel distribution, but you still don’t know that you will get even N2O distribution so you may get a bad mixture in one or more of the cylinders.

The reason that most systems tend to recommend retarding the timing on spray is for a combination of reasons. OEM timing is usually set pretty close to the ragged edge of what would detonate, since this is usually where the engine gets best gas mileage. As a matter of fact, many have found that even using a timing retard on an NA engine will give you a higher top speed and a slight MPH advantage through the traps. N2O augmented engines are notoriously insensitive to timing WRT to power production (often you can retard timing 10* or more with no difference in power production), but because of the increase in power, cylinder pressure… it is more sensitive to detonation and detonation will cause much more damage then NA. This all adds up to you don’t have anything to loose running retarded timing and you have a lot to loose (as in carrying your engine home in a bucket) running too much timing.

 

WRT the original question, for ‘normal’ shots of N2O (lets say under 150-200hp) compression… is not a real concern, assuming the rest of the package is well tuned. Compressions like what are used stock in LT1’s and similar engines are pretty much the ragged edge what could be used with a stock cam and pump gas, and they work fine with N2O and no tuning headaches. I’ve run a 175 shot through a stock LT1 with the only real mod for the N2O being plugs 2 steps cooler with no problems or evidence of detonation.