GCR 9.1.3.D.1.a.4 says, in part, "Air intake source shall be within the confines of the engine compartment or stock location." Define "the confines of the engine compartment".

GCR Technical Glossary (Appendix F) defines "engine compartment" as:

Engine Compartment – The loosely defined volume, nominally enclosed
by panels on top and sides, which is the normal location of the engine in
a car.

"Loosely defined", indeed. Question is, how loosely?

"So where's he going with this?" you may ask. I had an email exchange with someone, asking about the compliance to the ITCS of the Jackson Racing intake system for the Miata. He had seen it in other Miatae for sale and wanted to know if he could install it on his own car. Photo, installed:

http://www.miataturbo.net/attachment...as-2u5q0ox-jpg

This appears to pull intake air from above the radiator support. At first glance, I'd call it non-compliant, however nowhere is there a clear delineation of "engine compartment" for the front or bottom, and in this particular case the "top" is the hood, and this parts sits under that.

We briefly touched on the subject in the 2008 discussion of the ARRC CRX fender well intake protest. Within that, we recognized that there was some ambiguity, but never truly delved upon it.

Stock 1.8L engine compartment:
http://carphotos.cardomain.com/ride_...ata_engine.jpg

Stock 1.6L engine compartment:
http://www.practicaltech.ca/jpg/auto...engine-bay.jpg

Since the top of the "engine compartment" is inferentially defined by the Technical Glossary as the bottom of the hood, and this part fits within that without modification, isn't anything under the hood part of the "engine compartment"? If so, where does that allowance end in the forward direction?

And what about "prohibited function"? The regs clearly indicate that pulling air from outside the "engine compartment" is clearly prohibited, and the regs further clarify that you cannot run a minimal radiator to make open space to route air to the engine intake. But what if you are not modifying anything to grab air from that area?

About the only thing I can suggest is that it's non-compliant because the "engine compartment" definition in the Glossary states "the normal location of the engine in a car", and there's no way that the area above and in front of the radiator is a normal location for the engine. But it's not clear where that "normal location" definition ends, nor is it clear if that definition changes based on make/model (and if it does, then any space that the engine does not "normally" occupy - basically all the clear space around the engine - would not be allowable places from which to source air.)

Is it the aft edge of the radiator? Does that change with the allowed radiator design change? Is it the aft edge of the radiator support? Of the forward edge of the rad support? And if that part were trimmed back an inch to that plane, but still pulled air from above the radiator and radiator support, would it then be compliant?

I'm torn. Without using much intorturation, I see how this could be allowed, as-is.

I'm sure no one else on this board will have a strong opinion on it, but figured I'd ask anyway...

GA