I've been slacking on posting here, but I have been working on the car whenever I can. The next project was supposed to be the AC compressor & oil pan in one unit of work. I made the decision I wanted a temp sensor in the pan, which led to an order with CRF and lead time to have them temp-bung the oil pan. I figured I'd take on another project while waiting.
I'd like to take the car to the track next year, and there are 3 main things preventing me from doing that:
1. Water temps could get out of control
2. Air temps are too damn high
3. ABS no worky
I'll deal with water temps via an upgraded radiator in the next few months (Masiv when it is available again). ABS will get the upgrade early next year. To manage air temps with the SC I have, water / meth injection (WMI) seems like the only option.
I'm currently in the process of installing a water / meth kit.
Water / meth kit
Before I bought anything, I did a ton of research. Really hoping the feds don't show up to the house for all those 'meth' google searches. I guess I should put a hold on any sudafed purchases for now...
There are a million kits, the option to piece together your own kit, and generally a ton of considerations, so it took a while to get a hold on what I wanted. The main things I was looking for were: simple and reliable once installed. This is a whole new system, which means opportunity for bugs and maintenance.
Spray n pray
Okay, where to start? There are basically 2 approaches companies take to controlling the spray:
PWM the pump. This is the most common approach. All companies other than Aquamist do this: AEM, snow performance, devils own, etc. This gist is that the nozzle is directly tied to the output of the pump, and the controller varies the pump speed to vary the spray. It's kind of a crude way to spray, but it obviously works; 99% of installs are using this approach. The benefits here are that the pump is only running when you are spraying. This makes sense for a street car which is rarely in boost. The downside is that the spray is not so precise, but based on my reading, it feels like super precision isn't really required with water injection.
Constant pump speed, PWM a solenoid at the nozzle. This is basically how your fuel injection works: keep a constant pressure, then vary the duty cycle of a solenoid to vary the spray. Aquamist uses this approach. There are probably some boutique controllers out there that do this as well, but I ignored anything that wasn't in a kit. The big benefits are that it's more precise, plus is generally 'safer' in that you wont have the nozzle leaking into the intake tract due to gravity, which is a common problem on the pump PWMing approach (e.g. read the AEM 30-3300 amazon reviews...). The downside to keeping a constant pressure in the lines is that you need to run the pump all the time, even when you're not spraying. Maybe not so practical for a street car.
Control
Beyond the actual pump & nozzle setup, what controller should I run? What parameters should I vary the spray on? Can I get away without a controller? e.g. Can I just deal with it in the ECU?
I really wanted to skip using a controller if I didn't need it. Say I had the eventual Haltech 2500, which has a built in water/meth function, would I need a controller? If not how do people set that up? The short answer: they (most people?) still use a controller by sending the ECU's water/meth PWM out to the controller. I didn't find anyone with a simple setup running from the ECU only. Maybe it exists, if you have seen it, let me know.
In any case, PWM out from the ECU into a controller was The Move, ideally such that I could vary the output from the ECU based on RPM and boost. You know, like a fuel map.
This narrowed it down to basically 2 options: Aquamist or AEM 30-3350. Both of them take one of the ECU's injector outputs as an input, and can be progressive based on injector duty cycle.
For a while I was sold on the Aquamist. The internet at large pretty unanimously regards it as the "best" WMI option. There are no reports of it hydrolocking any engines, it's controlled by injector duty by default, and the benefits of PWMing a solenoid at the nozzle were obvious. All good things. Buuut in the end I wound up with the AEM unit, despite AEM being right up there with Comcast on my list of top 5 least-favorite companies. The reasons:
* I didn't want to run the pump all the time. It was unclear if the Aquamist had a switch to turn the pump off when I wasn't using it, or if it was automatic. I dunno, seemed like some cognitive load there if I were switching it on and off.
* Aquamist requires that you run a gauge. I don't want no more gauges.
* Aquamist has built in 'maps' based on injector duty cycle. My plan is to control the WMI with staged injection from my AEM ECU, so I'd have total control over the map, and these built in maps would be annoying. The AEM controller is way dumber, which is nice. There is a knob for start duty cycle, and another for full spray duty. Easy, linear, and then I tune it in the ECU.
* Aquamist is like 1 guy, which made me nervous for availability and support reasons.
* AEM sells an optional solenoid to run at the nozzle that solves the leakage issue. It's cheap enough where it should just be included in the kit, I bet the amazon reviews would be a lot better if it were.
* The AEM tank actually fit in the space I wanted. I was planning on running the Aquamist baffled tank no matter what, but it is too long (13" square).
* I have it in my head that AEM's latest V3 nozzle is actually better in atomization than other nozzles out there. But It's probably just marketing nonsense I've internalized because I watched more videos with AEM stuff.
The verdict:
* AEM 30-3350, with optional solenoid and inline filter
* Run it off the 7th injector output using the staged injection feature of the ECU
Where to spray??
One of the many considerations is: where to put that dang nozzle? I wanted to sort this out before I bought anything. My location options in order of most desirable to least
1. After the supercharger. Install a sandwich plate between the SC and the manifold, put the nozzle in the sandwich plate. Mainlining the meth straight into the engine, it shouldn't waste any juice cooling down the metal bits like the SC itself or intake tract.
2. In the SC snout. Get a bung welded in on the SC snout and run the nozzle after the throttle plate. It's a pretty straight shot into the SC.
3. Before throttle-body. Similar to the SC snout way, but probably absorbs more heat before it gets into the manifold.
Unfortunately those options are also in order from hardest to easiest. I know the NSX community has a strong preference toward the post-SC sandwich plate. But the rest of the world tends to run the nozzle pre-TB. In fact the AEM instructions mention, in bold, to put it before the throttle plate.
Because it will be so much easier, I'm going to run the nozzle in the silicone hose between the airbox and TB. The jury is still out on exactly how I'll mount it, but I have a couple ideas and some parts in the mail. If it sucks and I don't get great temp drop or stabilization, then I'll consider the harder options.
What about the rotors? Can you spray into the SC? After reading a bunch on the internet,
I'm not super concerned with it. Nearly all SC setups with WMI injection spray into the supercharger, and there doesn't look to be any major drawbacks. The rotor coating may be stripped faster, but even that doesn't seem like a problem. I'll mostly be running water, so maybe less of an issue?
