Too rich with the nitrous

[Dave]

You've got some good points, but in the end, putting both the nitrous and fuel into the runner is your best bet. With this configuration, you are all but assured that they will go into the cylinder they are sprayed towards.

The CAT is so slow that it I often wonder if it serves a useful purpose! Also, air temp sensors tend to add timing when they are cold, so that isn't a "feature" we'd want to exploit, thankfully they ARE so slow as to not create issues with systems that do "hit" them.

Nitrous will flow through the intake in pretty much the same manner/flow path as air (it is only slightly heavier than air), but that also means that if there is a flow balance problem with the intake, it can be amplified when the nitrous is on.

So far as the nitrous and fuel being "married", that lasts about as long as things are moving in a straight line, once it has to turn, fuel tends to drop out or splatter against the outside curve of the runner or other part of the intake, the more severe the turn, the more "loss" of fuel will occur. Then you have liquid fuel running through the intake. While not generally harmful in itself, the liquid fuel doesn't burn properly, effectively making things leaner, even though the proper lb/hr of fuel was injected. Most of the time, these "wet" systems have enough extra fuel from the system and the engine's injection to cover a lean hole and prevent a backfire or other damage. But the bigger the hit the less coverage you have and the more likely you are to have a lean-out/backfire. This is also why I generally recommend switching to a direct port system around 75-100 HP, which is about the point where distribution of fuel can start to become a real problem. It is also the point at which the smallest fuel jets will not be too much fuel. At 40+ PSI, even a .014" jet flows a lot of fuel!

We did do some experimenting with injection of the fuel in the runner with the bulk of the nitrous in the plenum, which made good HP, but was difficult to tune and still required gaseous nitrous at the nozzle to atomize the fuel. Exactly why it made better HP was never proven, but is thought to be due to two things, cooler/denser charge in the plenum allowed "more stuff" to get through the intake, the other is that the streams of nitrous pointed down the runners accelerated/entrained air improving the volumetric efficiency... But, in the end, the complication and marginal improvement of the system caused it to be abandon.

Hope that helps more than confuses!

Mike

Awesome knowledge here. I often wondered this myself... a lot of companies, I know, don't recommend a Wet shot if the fuel is going to be distributed through the intake manifold. I suppose my biggest comparisons are those of carb'd setups. IE a nitrous plate, or even the carb itself distributes fuel through the intake. Such as a dual plane might have would have more turns than anything other carb'd intake manifold.

Zin, any thoughts here?

Also, when going to a wet shot do you leave the jetting the same per nozzle? Say, right now we have a single fogger wet nozzle rated at a 55 HP shot. If we want to keep it a 55 shot but in a direct port 4 cylinder application, do we just simply divide the jetting in 1/4's? Or how does that work?

[zin]

Awesome knowledge here. I often wondered this myself... a lot of companies, I know, don't recommend a Wet shot if the fuel is going to be distributed through the intake manifold. I suppose my biggest comparisons are those of carb'd setups. IE a nitrous plate, or even the carb itself distributes fuel through the intake. Such as a dual plane might have would have more turns than anything other carb'd intake manifold.

Zin, any thoughts here?

Also, when going to a wet shot do you leave the jetting the same per nozzle? Say, right now we have a single fogger wet nozzle rated at a 55 HP shot. If we want to keep it a 55 shot but in a direct port 4 cylinder application, do we just simply divide the jetting in 1/4's? Or how does that work?

The big difference between a carb'd intake and our EFI intakes is that the carb'd intake was designed from the start to flow fuel, and so they tend to have more gradual bends and transitions, in an effort to keep the fuel in suspension, but since an EFI intake is not expected to have fuel going through it, they tend to have much tighter, and complex runners. Since nitrous is very close to air as far as weight goes, it follows very closely, not so much for fuel. I like to use the school bus(fuel) vs. Ferrari(nitrous) analogy, in a straight line at 60mph, not much difference, they'll both stick with each other, but, that hairpin curve coming up? well, at 60MPH the Ferrari is going to make it, but that school bus? Well, lets just hope there weren't any kids on board! Now, design the track to accommodate the school bus and everyone is happy, but design it for the Ferrari and that bus is going to be balled-up in short order!

As for jetting a single to a multi-port system. You'll need to divide the flow AREA to the 4 (or however many) nozzles. There is a formula to do this:

Jet size X Jet size, then square rooted, and then divided by the number of nozzles to be used. As an example: split up an 82 jet to 8 nozzles. 28 x 28= 784, square rooted= 28 So, eight 28 jets will have the same flow area/hp as a single 82 jet.

OK, now for the cheat! For 4 cylinders ONLY, just divide the single jet in half!

Mike

[Dave]

Thank you. Makes great sense.

[contraption22]

Mike (ZIN),

To bring back an old thread,

Is there any way to make a dry shot work without completely reengineering our fuel systems, short of a custom cal?

[zin]

Mike (ZIN),

To bring back an old thread,

Is there any way to make a dry shot work without completely re-engineering our fuel systems, short of a custom cal?

Sure, the trick is to keep the boost pressure consistent. In a non-cal application, you'll most commonly, need to boost the fuel pressure above "normal", this adds the extra fuel for the nitrous. The amount of HP/nitrous is limited by the amount of fuel you can get though boosting the pressure. 80-85PSI is pretty much the max you can go, though some have gone higher, I think it is a good compromise with safety and max HP.

You need to test to see what your maximum fuel pressure is when @ full boost, then we can see what kind of "overhead" we have for adding nitrous. I'd start small, something like a 28 jet.

This is small enough to potentially do something but small enough to ensure we can't hurt anything. At the same time, it gives us an idea as to how much fuel we have to work with.

The best way to tune is by spark-plug color/indications. But, that method of cutting the engine off clean, isn't too kind to turbos, so a wide-band O2 is the next best thing. 10.5-11:1 is typical for heavy nitrous/turbo applications, but I would expect this application would prefer something in the 11-12:1 range. And, I would still look at the plugs for any signs of detonation, which is more likely to hurt an engine than running lean...

Another way to get the needed fuel is to fool the computer into adding extra fuel by modifying the coolant temp sensor's signal into making the computer think it's -20* out.

The first way I mentioned is the easiest, as there is a kit made to do just this, the NOS 05115, made for 5.0L Fords, though it can be made to work on anything using a vacuum/boost referenced fuel pressure regulator.

The second method is how we did our Neon (05182nos) and the Viper kits (05180nos). They worked great, but are a little more involved, but not too much.

Interestingly, you could do both!! Of course, you'd need a top-notch fuel pump to do it!

If anyone would like to know more, feel free to PM me or we could start a new thread...

Mike

[puppet]

What about a 3 way solenoid valve plumbed into the fuel return line? One leg on the valve can be restricted with a jet ... raising the fuel pressure. Could be switched with the nitrous system. Boost requirements stay proportional.

[zin]

What about a 3 way solenoid valve plumbed into the fuel return line? One leg on the valve can be restricted with a jet ... raising the fuel pressure. Could be switched with the nitrous system. Boost requirements stay proportional.

That's pretty much what the normal system does, but the problem you would run into is that a simple restricter jet won't maintain a particular pressure. It will spike it, but as the injectors open more and more, you'd loose more and more pressure, at a point that you need it the most. Boosting fuel pressure via the fuel regulator involves pressurizing the regulator, just like boost does, but to a higher degree, and without the counterbalancing pressure of boost, resulting in a "step-up" type of pressure increase, one that stays constant regardless of the injector flow rate (assuming an adequate fuel pump/system).

Now, if you put a Grainger type check valve in the line as the restricter "jet", it would work in the same way as the commercial system, adjusting the amount of by-passed fuel to maintain whatever pressure it was set to. One difference would be that the pressure the regulator's diaphragm sees from the fuel pressure boost would not be "balanced" by pressure on the "air" side of the diaphragm, which might be detrimental to it's longevity... But it would work.

Mike

[contraption22]

Started a new thread here.

http://www.turbo-mopar.com/forums/sh...196#post651196

[Dave]

I'm going to start playing with this soon. Problem is I don't know how much smaller I really can go with a 55shot. Per Zex, the fuel jet is .17". They only go down to .15". Not much smaller. I may try another brand which allows a smaller fuel jet............................................... ........

OR...........................

Bigger nitrous jet!

Mike, any thoughts on a maximum safe amount with a wet shot through an EFI manifold? I'd imagine no fuel in the manifold is best but I'd like to hear your thoughts? I'm mostly concerned with even distribution once we get to a bigger shot.

And we're getting a computer flashed for it... I'm thinking retarding 2* of timing for our current 55 shot? Venolia pistons with a stock CC G-head... I forget the static compression of that setup though.

[Dave]

Shabump?

[zin]

I'm going to start playing with this soon. Problem is I don't know how much smaller I really can go with a 55shot. Per Zex, the fuel jet is .17". They only go down to .15". Not much smaller. I may try another brand which allows a smaller fuel jet............................................... ........

OR...........................

Bigger nitrous jet!

Mike, any thoughts on a maximum safe amount with a wet shot through an EFI manifold? I'd imagine no fuel in the manifold is best but I'd like to hear your thoughts? I'm mostly concerned with even distribution once we get to a bigger shot.

And we're getting a computer flashed for it... I'm thinking retarding 2* of timing for our current 55 shot? Venolia pistons with a stock CC G-head... I forget the static compression of that setup though.

Your pretty much on target with your assumptions, dry is better than wet. Incidentally, if you go dry, you'll want to inject the nitrous just after the intercooler, this gives the maximum time for the nitrous to cool and mix with the air ensuring as even a mixture as the intake manifold will allow.

As to max HP with a wet system... That's a bit of a loaded question! I've seen some folks get away with things that they really shouldn't have, but if I had to throw out a number, I'd say somewhere in the 100HP range, and no higher... Direct port will cure this problem as it is a question of distribution more than anything else, assuming the bottom end is built to handle the abuse. The number 1 issue with these systems (single point wet), is that the fuel won't get to all the runners evenly. At low HP levels, say 30-50HP, there is enough "extra" fuel from the injectors to "cover" a lean hole caused by the poor distribution. The problem is that as the system is jetted up and up, the amount of "cover" fuel stays the same, which inches that cylinder closer and closer to a backfire... So, that's why we will advise someone to either go direct port, or keep it smallish.

As you probably already know, a 50HP combo on a turbo car can easily pan out to be 75HP or so at the wheels due to the added intercooling and boost efficiency.

You are on the right track regarding adjusting the tune-up, and the timing seems fine too...

A little side note about ignition timing: All engines make best power when they develop peak cylinder pressure around 15-20* aTDC. This is true for just about every spark engine you'll deal with. We often run the total timing in the 35* (bTDC) range in order to achieve peak pressure in the 15-20* range. Nitrous is unique in that it chemically adds oxygen, more oxygen means you can burn more fuel, but since the ratio goes higher (N2O has approx. 14% more O2 than air), the burn rate also goes up. This faster burn means we need to light the mixture later to still achieve the peak pressure at 15-20* aTDC, to what degree depends on how much nitrous is added, and to a lesser degree, chamber design, etc.

We have found that retarding the timing 2* per 50HP of nitrous added, will pretty much guarantee that the timing won't be too much, in fact, it will likely be substantially less than it could be. Most will find best power with 1-1.5* retard from the engine's best "motor-only/non-nitrous" timing.

It is worth noting that the reason we start with more retard than needed is that it will result in only a loss in power and response due to the peak pressure happening latter, say 20-25*aTDC. Too much timing, just like with a turbo or supercharger (or NA for that matter!) will kill an engine faster than anything else you can do, short of a stick of dynamite or a .50BMG round!

Mike

[Dave]

Your pretty much on target with your assumptions, dry is better than wet. Incidentally, if you go dry, you'll want to inject the nitrous just after the intercooler, this gives the maximum time for the nitrous to cool and mix with the air ensuring as even a mixture as the intake manifold will allow.

As to max HP with a wet system... That's a bit of a loaded question! I've seen some folks get away with things that they really shouldn't have, but if I had to throw out a number, I'd say somewhere in the 100HP range, and no higher... Direct port will cure this problem as it is a question of distribution more than anything else, assuming the bottom end is built to handle the abuse. The number 1 issue with these systems (single point wet), is that the fuel won't get to all the runners evenly. At low HP levels, say 30-50HP, there is enough "extra" fuel from the injectors to "cover" a lean hole caused by the poor distribution. The problem is that as the system is jetted up and up, the amount of "cover" fuel stays the same, which inches that cylinder closer and closer to a backfire... So, that's why we will advise someone to either go direct port, or keep it smallish.

As you probably already know, a 50HP combo on a turbo car can easily pan out to be 75HP or so at the wheels due to the added intercooling and boost efficiency.

You are on the right track regarding adjusting the tune-up, and the timing seems fine too...

A little side note about ignition timing: All engines make best power when they develop peak cylinder pressure around 15-20* aTDC. This is true for just about every spark engine you'll deal with. We often run the total timing in the 35* (bTDC) range in order to achieve peak pressure in the 15-20* range. Nitrous is unique in that it chemically adds oxygen, more oxygen means you can burn more fuel, but since the ratio goes higher (N2O has approx. 14% more O2 than air), the burn rate also goes up. This faster burn means we need to light the mixture later to still achieve the peak pressure at 15-20* aTDC, to what degree depends on how much nitrous is added, and to a lesser degree, chamber design, etc.

We have found that retarding the timing 2* per 50HP of nitrous added, will pretty much guarantee that the timing won't be too much, in fact, it will likely be substantially less than it could be. Most will find best power with 1-1.5* retard from the engine's best "motor-only/non-nitrous" timing.

It is worth noting that the reason we start with more retard than needed is that it will result in only a loss in power and response due to the peak pressure happening latter, say 20-25*aTDC. Too much timing, just like with a turbo or supercharger (or NA for that matter!) will kill an engine faster than anything else you can do, short of a stick of dynamite or a .50BMG round!

Mike

Good stuff like always, Mike!

Thanks again. Onwards we go with the bottle then!

[zin]

Good stuff like always, Mike!

Thanks again. Onwards we go with the bottle then!

Thanks! Happy to help!

Mike