I bet if I stuck an SR20DE in my 240SX, I could go all season locally without anybody even batting an eye. Why? Cause it says Nissan on the valve cover and it bolts in stock. (The car came with this engine in every other country it was sold.) I can provide a bazillion pictures of this engine in this chassis, including a service manual in Engrish with drawings of this engine in the chassis and everything.
The guys in tech can't possibly know every car and every US engine that's on the market, so it's nearly impossible to police this kind of stuff.
I haven't been asked to lift my hood by anyone since I got my logbook for the car back in May. Of course I've only run regionals so far, but it's not like I'm an also-ran. I've finished in the top 5 overall and won STU in all but one race to date, as well as set track record at MSR-Houston.
Nonetheless, I could have been running a freakin Chevy V8 in the car all season and nobody would know..
But am I for non-US engines? HELL YES. Nissan's engine options under 3L are crapola for the US. everything is a long-stroke truck engine, or an ancient iron block designed in the 60s. for a supposedly modern class and philosophy, Nissan is stuck with engines from the stone ages.
Do I realize it would open up the class to all kinds of other uber-engines? You betcha. Bring 'em on.
Let's go back to the rules when they were originally made for the class: (This is STU-specific..)
Normally aspirated:
Under 3.0L displacement
12.0:1 max compression
0.6" max valve lift
6 spd max transmission.
weight = 1.1lb / cc displacement
Go.
Turbo?
stock turbo for the engine it came on. no conversions.
pick a tranny, 6 spds max.
weight is based on inlet restrictor size placed in turbo.
Go.
For whatever engine you have, you must a factory service manual in English in your possession.
Very simple to police. All of the components are easy to measure and/or verify with a factory manual. Voila.