A few comments from my own experience. I've had a Snow Performance kit fitted to my
Mk1 Leon for over two years.
Yes, it does what it says on the tin. Used to cool the intake charge, the results are astounding. I have a FMIC, but I reckon running WMI with a stage 1 map and standard intercooler you'd not have to worry about intercooler improvements.
It takes time to get it right. I started out with the nearest sized nozzle for my set up, running 50/50 water methanol. Shortly after, we ran the car on a Rolling Road. We quickly proved that the car made about 35 bhp
less with the wmi running than with it turned on! Reason - too much methanol - it was quenching combution. I'll say this time and time again, don't get over-enthusiastic. It's easy to inject too much methanol. I went away and experimented with logging for months. I ran a 25% mix of methanol for a while, then 33% for a long while.
If the methanol is injected too early in the spool up, this will also quench the charge.
Always mix with distilled water. The methanol seems to make limescale precipitate out and clog the nozzle filters.
Treat Methanol with great respect. It's a nasty poison - google and have a good read on methanol poisoning. It can be ingested through the skin. Also, you can't see when it's burning, the flame is invisible. Mixes greater than 50/50 are flammable.
With much experimentation, I finally got my system (boost pressure driven) to the stage wher I could start advancing the ignition timing. Log and check, log and check. Too much advance = Correction factors. I finally got the system to the stage where I am running 8.5 degrees of ignition advance. I believe I am getting close to 30bhp extra from this.
My map is not written for wmi. At some point, I intend to get it custom mapped to suit.
I now have a safety system which will drop boost to actuator pressure should the methanol stop flowing.