Indepth study of WAI injection systems -restart

[Aquamist]

Thanks for chiming in, it is so nice for be able to discuss this - I want to learn more.

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I would like to add my experience to the discussion. From what we've experienced, the further away from the TB the better, with the exception of the BOV issue. Here are a few rough calc's and an example.

Using the numbers a couple of posts ago, 40lbs/min and a 2.5" ID pipe for simplicity, the air is roughly at 177mph or 3128 inches per second of travel. This means each inch of air passes the jet in roughly .0003sec. At the molecular level of evaporation, this is quite a long time.

For example, a 24" diameter tire makes about 845 revolutions per mile. With a 75" circumfrence, this means each 1" of tire is in contact with the ground for .0005 seconds. Since the contact patch is about 4" long, this means the 1" of tire is in contact for .002 seconds. This is still ample time for the rubber in the tire to create molecluar bonds with the surface(one a few forces generating grip) and break the bonds. Since certain tires can operate at twice this speed we know that the molecular forces can act very quickly.

Back to the jet placement, the evaporation and cooling of the charge, in general, due to mix and charge temp/velocity, begins almost instantaneously. Looking at the 24" pipe before the TB, my guess would be if you looked at the temperture profile of the air in the inlet track, a good deal of the cooling would occur before the TB. Given more water injected, it is even more important to allow for adequate mixing before any separation or sharp bending of the charge flow occurs.

I ran these on a napkin, so if I missed a decimal place or number, feel free to correct me.

[Aquamist]

That made a lot more sense. I have had experience experimenting with jet locations in the past on WRC cars. The exit of the intercooler was the preferred postion. BOV or dump valve is often the internal recirculating type.

I wonder if anyone with TB installation can chime in with their experiences?

[SnowTech]

Originally Posted by J Howerton

I would like to add my experience to the discussion. From what we've experienced, the further away from the TB the better, with the exception of the BOV issue. Here are a few rough calc's and an example.

Using the numbers a couple of posts ago, 40lbs/min and a 2.5" ID pipe for simplicity, the air is roughly at 177mph or 3128 inches per second of travel. This means each inch of air passes the jet in roughly .0003sec. At the molecular level of evaporation, this is quite a long time.

Pretty good calcs! But what you have to consider is the amount of time the air spends post TB and pre-cylinder heads. This will be much longer in a lof of cases where you have a fairly large aftermarket plenum chamber relative to a normal size IC pipe. So lets say we get a nozzle a full 2 feet before the TB, you then have about .007 seconds by those calcs before it is past the TB. You likely have much more than that long between the TB and the intake valve, which is where a lot of the cooling will occur.

The other thing to consider is that cooling in the combustion chamber is often just as important in these applications as it is in the intake plumbing. The cooler air charge before the intake valve will help get more 02 in, and basically help with volumetric efficiency. But the detonation prevention aspects of reduced cylinder temps are at least as important, particularly if we have a FMIC in place already. And when you look at the time spent in the combustion chamber, and the pressures, temperatures, and flow characteristics inside the chamber, every last bit of the liquid is going to absorb as much as it possibly can (unless something is very wrong).

In the end it is spliting hairs a bit, and a nozzle right after the IC might have the benefit of showing a bit more cooling on an IAT sensor. So really its more of a case by case basis. Most of our customers find that the biggest concern regarding placement is more of an installation and functional one rather than the theoretical, even when they do have an FMIC.

Great discussion guys!

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Originally Posted by SnowTech

In the end it is spliting hairs a bit, and a nozzle right after the IC might have the benefit of showing a bit more cooling on an IAT sensor. So really its more of a case by case basis. Most of our customers find that the biggest concern regarding placement is more of an installation and functional one rather than the theoretical, even when they do have an FMIC.

Great discussion guys!

Indeed, it is splitting hairs to a degree. If one were to instrument the 24" pipe after the jet you would see significant cooling, but you would also be measuring wet bulb temp, which is not entirely correct.

I might add one item to what you noted. If you are relying on a mix with ample water to cool combustion temps, the farther you can put the jet form the TB the longer time there is to strip the molecules down to smaller size to stay in suspension in the air making turns. The Subaru suffers much less from this with it's manifold design, but log style manifolds can have issues with heavy water mixtures distributing evenly. Much of this is theory without clear intake manifolds, dye infused mixtures, and much instrumentation.

What we see in reality is much the same as you, a practical placement of the unit usually out weighs the theoretical best. I'd even add that placing the jet in a location for proper maintenance, within reason, is probably wiser in the long run than a hard to get to but theoretically better location.

[subieslam]

wow good info being shared. so that covers turbo cars... what about cars with positive displacement superchargers? inject pre- or post-blower? and why?

[SnowTech]

You can go either way there. We usually go pre-blower for two major reasons:

1) This allows you to cool the blower case and the air charge, which does a lot for under-hood temps. In many cases it actually gets a bit more boost from the blower as well. I had one customer with a Jag that claim he picked up 4 psig that way. The blower in that case was being drastically overspun (And Eaton making 20-24 psig on a 4L V8).

2) It is much easier from an installation standpoint as well in many cases, as there is no need to remove the blower etc.

We do NOT recomend injection pre-compressor on turbos or even centrifugal blowers, as they are a completely different system with much higher velocities involved and of course the thin compressor blades. If you look around online you can find pictures of the damage from over-injection pre-compressor with a high RPM turbo. On many of these applications you have the tips of the compressor blades moving at 900+ MPH. IF you then start hitting that leading edge with a droplet of liquid (even partially evaporated) you can cause issues.

The thing about spraying pre-blower on a positive displacement unit (like a Whipple, Eaton, KB, etc) is that these blowers do make a lot of heat relative to a properly sized turbo. So the injection volume is often much higher. An employee here had an '04 Mustang Cobra that we did a lot of work with. That car was fairly stock, at this altatude probably only in the range of 500HP and a bit more than stock boost. Yet it would handle a 625 nozzle just fine. A 375 probably would have been more appropriate had it been a centrifugal car at the same overall power and boost levels.

[Aquamist]

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[Aquamist]

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[Aquamist]

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We have done quite a bit of intensive data logging(I won't bore you with the details) on roots SC cars and some on centrifugal's, and same as turbo cars, it can be very application specific.

One rule of thumb that seems to hold is boost based water/meth systems on roots cars are difficult to get the most out of. You can get a high percentage of max boost near instantly at low RPM. So you have to either set the boost based systems to spray correctly in the midrange, in which you are lacking in some jetting on the top end giving up power, or you jet correctly for the top end and drown out the midrange losing TQ. The roots cars really like an IDC based system to meter injection though the entire rev range, or at a minimum a MAF based injection scheme.

Where you put the jets and what mixture you spray then gets more car and power level specific. I do agree with Snow, the roots cars put out a lot of heat and can tolerate more jetting.

[SnowTech]

Originally Posted by J Howerton

We have done quite a bit of intensive data logging(I won't bore you with the details) on roots SC cars and some on centrifugal's, and same as turbo cars, it can be very application specific.

One rule of thumb that seems to hold is boost based water/meth systems on roots cars are difficult to get the most out of. You can get a high percentage of max boost near instantly at low RPM. So you have to either set the boost based systems to spray correctly in the midrange, in which you are lacking in some jetting on the top end giving up power, or you jet correctly for the top end and drown out the midrange losing TQ. The roots cars really like an IDC based system to meter injection though the entire rev range, or at a minimum a MAF based injection scheme.

Where you put the jets and what mixture you spray then gets more car and power level specific. I do agree with Snow, the roots cars put out a lot of heat and can tolerate more jetting.

We have found that too. We started going with MAF based injection on positive displacement setups and also quick spooling turbos years ago because of the need to have a large jet without bogging on the low end. A boost based system can still be very effective, but it is a bit tricky to dial in and find the happy medium. This is one reason we also do a PW/Boost referenced system in so many applications as well.

I will look over the charts as time permits Its not a matter of patience, as I love that stuff. It's just trying to get everything done as the year comes to close.

[Aquamist]

It is confusing for anyone who enters the WMI application from the cold. This link may help you looking into various technologies available to date.

[JMlegacy]

I'm guesstimating that the MAF based PWM valve system used with pure water can see similar performance as non-progressive water+meth or 100% meth. Why? More water = more cooling but we all know that water cannot burn, so if we use a non progressive system with a big jet, the midrange will bog and misfire even though the top end would love it. With a airflow based progressive system the engine won't have to deal with a dump, it can scale it to match airflow.

I don't believe methanol adds that much "octane" to the mixture. I believe it simply cools the charge and cylinder that much better than water because we can use a lot more without misfire.

But all this is just my understanding and opinion. I'd love to see a dyno comparison of the two

[punkmonkey187]

very helpful