@msjulie I have an OutFront EJ-25 motor in my VMC Pre-A coupe (delivered this fall I think-hope-pray). I have lots of notes on why I went Subaru and which motor with which mods in my build thread (here's a link: LINK). I've used the thread to capture some of my thinking on each of the car's systems and share it. I was just working on a post about the engine management aspects of the car for that thread that I hope to have up soon. In a nutshell I have a US EJ-25 block with head mods and a Stinger ECU (now branded as Link I believe). The unit has 4 auxiliary outputs that will drive a cold start solenoid, fan on/off for temp, fan on with AC clutch, and that kind of thing. John has done a lot of tunes on these, and even more since working with Carey, so I'm confident he'll give me what we talked about. Carey has got a point, if you're building lots of Suby powered things then a stock ECU with the fly-by wire pedal is the easy button that guarantees the most customer satisfaction for the least amount of worry and has almost universal DMV approval. With what I have coming the base tune was loaded before the engine was delivered. Once the car is ready to be driven on the road, the engine will be fine tuned on the dyno before delivery.
I was lucky enough to ride in a sand-rail with an OutFront Suby similar to mine (no AC of course, and no cold start solenoid). It ran great! Turn the key, push the button, and rup-rup-rup down off the trailer. It sat there idling smooth as silk with an ambient temp of 50 degrees (and had sat on the trailer for a week before that start). It idled and purred through what I guess one could call the paddock area like it was mom's station wagon, then got to the dunes and RIPPED! It was like that all weekend with cool morning temps and searing hot afternoons, hot starts, cold starts, it just didn't matter. I was really impressed. I would also point one towards Michael Pickett's FI system he built for an air-cooled type one motor to calm fears that ECU tuning is really hard. It's like this: Some folks like Stan and Danny are good at, and want to tune carbs. I did it on race bikes and I don't want to do it anymore. I know the whole computer aspect of tuning Fi is a turn-off for some, but other folks like to fiddle with the timing and mixture from a laptop (I probably fall into this band of weird-o's although I don't anticipate messing much with this one). Many (most) don't want to fool around at all. ANY good FI system will be a better choice for the last group. A stock system will be the easiest to diagnose (CAN-bus port) when a sensor fails. It's the simplest option if one can live with a drive by wire throttle and what the stock ECU does to induce throttle lag, etc. That's what killed that option for me. I HATED what the ECU would do when trying to heel and toe my MINI. The direct coupling of accelerator pedal to throttle butterfly is something I miss and feel is critical to the vintage driving experience.
Lastly, there is always a lot of fear about cooling. The beautiful nose of a speedster doesn't allow for a Mack truck upright radiator. The piping is long, and designing a system that doesn't trap air is an issue to be sure. I have confidence that Carey and Greg have worked all this out over many-many quality builds. But I will add my two cents. Cooling isn't just a function of how much radiator and how much volume. It is also a function of how stressed the motor is during use. Part of what makes these such a nice application for us is that a stock, or near stock, EJ-25 is under stressed in the extreme. The car is half the weight of a fully loaded Suby station wagon. A free flowing exhaust and intake will also help (an engine is also cooled by the air that passes through it). So I'm not any more worried than I am with any of my daily drivers. With a good system in place it all comes down to maintenance and having a good sense of mechanical simpatico for your car.
Hope that helps!
-Michael