Driving Aquamist 2c high speed valve with stand alone EMS

[max legroom]

I have a highly modified 2002 Subaru WRX, with forged internals, 9:1 compression ratio (stock is 8:1), and lots of other supporting mods. I'll be installing a Tec3 EMS (using full-sequential fuel injection) very soon and have an Aquamist 2C ready to go in at the same time.

There are 2 possible ways I can control the high speed valve. The Tec3 has a staged injection feature which links injector drivers 5,6,7 and 8 with drivers 1,2,3, and 4, respectively, using a load/rpm map to determine when and for how long to open staged injectors. Using this feature, the Aquamist high speed valve would be opened in sequence with only one of the cylinders, since only one driver can be connected to it.

The second possibility is to use one of the General Purpose Outputs to drive the valve, which could be configured to fire the valve with every cylinder.

Are there pros and cons to these two approaches? Which one would be best, and what size nozzle would be appropriate for each (assuming 15% water/alcohol mixture)?

[Charged Performance]

Yeah I can imagine if you are running any boost at all on the flat4 with that CR you are dying to get some detonation suppression or have a good account with a race gas supplier.

Theorectically, I suppose you could use the signals from drivers 5-8 even. Isolate the signals with diodes. Though at higher rpms the frequency may be too high for even the hsv. Maybe do a 5 & 8 or 6 & 7 signal this way.

Anyway I digress to your question. If you use just one driver, you will of course only be pulsing once every two rpms. On moderately tuned Subarus this should not been problematic given the long intake runners. However you are likely pushing much larger volumes of air and the related velocity may not allow for a uniform mixture. You could possibly get water leaner and richer cylinders, probably not the same ones every stroke while rpms are changing but still each cylinder would be water lean or water rich at one point or another especially at high rpm, high boost. This isn't good for detonation suppression or finding a stable timing setting. Again not a problem on moderate setups but high cfm setups could face this problem. The method I described above as well as your second method would mitigate this. My response here also assumes you are injecting at the throttle body. Clearly if you are injecting at an earlier point on a FMIC system for instance the water will have more time to become uniform before the plenum. Also the above is speculation since the plenum design and runner length has not been shown to cause a problem with getting uniform flow.

Provided the duty cycle could also be controlled the firing twice per rpm with each cylinder would be ideal since the mixture to each cylinder would be much more uniform. The issue again becomes whether or not the hsv could keep up with the frequency. It is rated at 250mhz or about 7500 rpms. However this also only leaves 4ms duty cycles. Take away 1ms to open and 1ms to close and you are down to 2ms of resolution for flow control. Not a great situation.

I think the best solution may be to go to 2 hsv's. Drive one with the 5&8 wires and the other with the 6&7 (using diodes to isolate betweent the paired driver wires). At a minimum that would result in 8ms cycles for each hsv allowing for 6ms of resolution for the flow control. In theory you could try drive these through one jet but are probably better of driving them through at least one jet for each hsv.

Just some thoughts.

[max legroom]

Thanks, Ed, for the interesting discussion. I will be raising the redline to take advantage of the new engine components and it is good to know that the hsv will not handle that frequency. I like your idea about using 2 hsv's and alternately firing them. Do you think the single pump that comes with the 2c will handle 2 valves and 2 jets?

[Richard L]

Hello John,

I like to point out the conclusion of the HSV not handling the frequency is quite misleading, here is my approach to the situation. The HSV's frequency response is almost identical to the WRX fuel injectors, if not slightly faster and higher flow.

Your WRX, an unusual approach to the norm - EMS-T3 is a complete takeover as I can see . Most people will be happy to buy a read-made (utec) or semi-made (reflash) package using existing downloadable map or asking a tuner to map it for them. Unfortunately 99.9% of the tuners out there are not adventurously enough to approach WI head-on, some use it as a safeguard for bad fuel and some just dis-approves it outright.

Injector speed: all 16 ohm fuel injector (wrx/sti) has an average opening and shutting time of around 2ms at 12V, the aquamist HSV is no different -this is not a design fault - it is to do with limited energy feeding into the coil to perform a mechanical action. The amount of energy applied to the valve is limited by voltage and coil impedance (resistance). As energy is power over time (V^2/R).

Assuming your are tapping into one cylinder of the T3, running sequential injection. At 6000RPM (100Hz), one of your fuel injector is firing at every two engine revolutions or an interval of 20ms (50Hz). The control-able range is between 2-28ms (taken into account of opening and shutting time). I cannot see any problems for the HSV or your injectors to run out of injection time. So far so good.

The main perceived problem is not the HSV unable to run fast enough but out-of sequence of the induction phasing intervals. In other word, the HSV is firing in phase with one injector and no water for the other three cylinders. This conclusion may hold true if the water jet is close to the inlet valve of the plenum chamber.

Let say if you place the water injector before the intercooler and immediately after it, the water droplets will take sometime to arrive at an individual cylinder, after passing through the satellite distribution chamber. The "no-water" gap is no longer clearly definable. Further factors such as rate of evaporation of drop size travelling at different speeds, rate of evaporation in the inlet tract and some speed reduction of the drop hitting the wall of the inlet tract. My conclusion is that it will not be a problem triggering the HSV with pulse from one injector. If you are still concerned about cylinder distribution, place two small water jets at few inches apart so that it will have the same effect of "filling-up" the gaps. One good method is placing another small jet in front of intercoolern and one after.

Your second choice of using the GPO - no problem at all - run at a fixed frequency of 32Hz or 64Hz, the HSV will deliver water effectively and evenly across the entire RPM range.

Why not running both (your suggestion) if you still have concerns, two HSV firing at opposite cylinder phase- intervals - cheaper to phase the mechanically (not bad) than electronically.

We need to talk about the faulty diagnostic functions you can perform with the GPIs later. If you are happy with my reply and would like to add some comments.

Even at 8000RPM, the inteval of the fuel injection pulse is approximately 14ms. The HSV will handle that with ease.

[Richard L]

my post merely reflect and comfirmed "charged-P's"

[max legroom]

Hello Richard,
Thanks for that clarification. Using two jets located a little distance apart in the intake path sounds like an ideal solution. I guess using 2 x .4 mm jets would be best, as that would give .32 sq-mm area, a little less than a single .6 mm jet. Do you think that's reasonable?

I thought about the utec and reflash options, but in both cases I'm stuck with the limitations of the stock ecu. I want to add wideband O2 and use MAP for load calculations, neither of which are possible with the stock ECU. I will also probably use some of the tec3's more esoteric features, like "Throttle position rate of change"... Sure, I could add a few thousand dollars of controllers (and design some custom electronics myself) on top of a reflash or utec, but putting all that together in a single unit like the Tec3 makes life simpler.

But the main reason I'm going in this direction is that I want to understand eveything about engine design and tuning. I did a lot of research last year, decided what I wanted the torque curve to look like when I'm done, then pulled my car into my garage and rebuilt the engine last winter. Now I'm ready to start tuning it to take real advantage of "my" engine. It runs well enough with the stock ECU (although open loop is less than optimal because the map is way too rich for the smaller combustion chamber) that I can drive it while installing the Tec3.

As for tuner's attitudes toward WI, i think in general you're right, many of them just don't get it.

[Charged Performance]

The two 0.4 might be a good place to start - step wise tuning is best unless you have a lot of WI tuning experience on a set up. But I do suspect that eventually you will eventually increase the size to two 0.5 or more. Remember you will have both pressure and jet size to adjust your flow rates.

Just a clarification by no means was I suggesting that the hsv is at all lacking as Richard said its performance is on par with most quality fuel injectors - just using one hsv to keep up with 2 injector pulses per revolution is asking too much of it. It should keep up with 1 per revolution fine. Hence the recommendation on the cross cylinder cycle injection.

I will be interested in seeing how the Tec3 tuning goes. If you haven't gotten it yet have you looked at the new hydra system from element tuning at all? http://www.elementtuning.com/main.htm

[max legroom]

Hi Ed,
Thanks for the advice on jet size. You're right, it would make sense to go with .5mm jets. I'm leaning toward using a GPO for hsv control, since that would allow me to stop firing the valve completely under light load/low rpm conditions and customize a map over the rest of the matrix. The .5mm jets should flow plenty of water, especially at high rpms when there's less time available, and if they're off at low rpms then I don't have to worry about exceedingly short on-times to keep water flow at a low rate.
It'll probably be mid May before I get everything installed and ready to tune (got other things I also need to do. Bummer...). I'll post my experiences as interesting things happen. In the meantime, other people's comments and experiences would be welcome.

[slowMX5]

I am running a TEC3 on a turbocharged MX5 (1.6L) with a stock 9.4:1 CR and 15psi of boost. I've been experimenting with a 2C over the last couple of months - with Richards help. I have ended up using 2 jets, one just post IC and the other just before the throttle body. I also started out with 0.4mm jets - but have since gradually moved up in jet size to deliver more water. Main reasons were the improved spray pattern once using 0.6mm jets and larger and the fact that when using the TEC3 to drive the HSV one can adjust duty cycle and hence flow. I am also experimenting with higher water flow rates (upto 400cc per min so far). At present I am using a 0.9mm jet and a 0.7mm jet, but will most likely replace the 0.7mm with a 0.9 or 1.0mm jet.

I have plenty of flow rates versus duty cycle for differing combinatins of jet size. My 0.9mm and 0.7mm jets will provide upto 470cc per min of water flow at 90% duty cycle.

Also when testing the flow I discovered that the jets continue to provide a mist down to about 15% duty cycle, any lower and the pattern suffers severly.

I have set things up using the GPIs so that the TEC3 only adds timing and leans the fuel when the TEC3 sees water flow. Currently it's flow or no flow - but I intend to try a linear relationship relating timing added/fuel pulled to flow rate soon.

If I can help any further then please ask.

[max legroom]

Hi Steve,
This is really interesting. It sounds like you've got a great car! I don't want to ask too many dumb questions, but it sounds like you've got a very well designed system using a GPO to control the hsv (I'm new to the Tec3, but I can't see any other way of tuning the water injection as you've described it except by using the GPO duty cycle table). My WRX has only a couple of inches between the intercooler and the throttle body. I apologize for my ignorance of the MX5 configuration, but how much distance is there between the intercooler and the throttle body, and what is the pipe diameter? I would also love some duty cycle information to understand how much water you're injecting and where in the load curve you're injecting it. Most people would think those jet sizes are very large for a 1.6 liter engine (and they would be right if you just pumped water through at a constant high pressure), but it sounds like you've done a great job configuring the injection duty cycle to control injection rate.
I'll post the findings with my configuration as I work things out, but I'd really appreciate more details on your setup.
Thanks for posting!

John G.