[A1337STI]

15.1 C 3. As utilized only on engines originally equipped with forced
induction, induction charge heat exchangers (known as “intercoolers”
or “charge air coolers (CACs)”) are unrestricted in
size and configuration. Air-to-air CACs and radiators for airto-
liquid CACs must be cooled only by the atmosphere, except
for standard parts. Body panels, fascias, or structural
members may not be cut or altered to facilitate CAC installation.

in SM there is no mention of intercoolers at all so i'de think this applies
16 (street Mod) B. Competitors may pick and choose between all Stock, Street
Touring, Street Prepared, and Street Modified allowances when
preparing an SM car. Apparent conflicts between inherited rule
sets from 16.1.A shall not prohibit any specific inherited allowance.
Allowances inherited from 16.1.A may not incorporate SMspecific
allowances. Foreign spec parts may not be used

(prepared)
17.3 D 3 Only air-to-air intercoolers may be used. They must fit completely
within the bodywork. They must be cooled only by the
atmosphere. The use of coolants such as water, dry ice, ice,
etc. is prohibited.

So nothing from stock to prepared seems to allow the exteral use of water on an IC if its not a factory part. the factory STI sprayer is a 3 second blast per button push. as long as you get the same manufactor free part swaps you should be legal in sm with the STI sprayer, but not an altered one. (course i could be missing some rule somewhere)

Modified doesn't specifically say that non factory IC sprayer, or the external use of Ice/water is / or is not allowed.. ?!? i have not really looked in that part of the rules much though.

some non factory IC sprayer is something i've been hoping to do but it looks like its Mod class or not allowed in autox. (ruling snafu ? or maybe they don't you to run on 80F charged air when its 90F out?)