Mixing and matching car models

I have a question about mixing of parts from various car models to make your own model utilizing the best stuff from each of the factory models. I thought that you couldn't do that.

For instance, here is a post that is a good example: (Sorry for using your post here, anonymous person, but it was exactly what I was looking for.)

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A few years ago, when I was running an all-S5 ('89) car, the concensus I was hearing was that the S4 ECU and AFM were superior to the S5 but the S5 intake and rotors were superior - so the hot setup was an early car w/ late engine. At the advice of one of the Fla. shops I went so far as to try to retrofit an early ECU and AFM into my '89 car.
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? I MUST be wrong on this, otherwise everyone wouldn't be doing it. But what exactly is the reasoning? I understand the rule is that you have to pick a car model, and that's what your car is. So you can't use parts from other models. Like you couldn't use a 5th gear from a GTUs unless your car was a GTUs. (Or you made your car into a GTUs.) That gear ratio only came in those cars. And if your car was a GTUs, then it didn't come with an early body, wiring harness, etc. Enquiring minds want to know!

If the cars are listed on the same spec line in the ITCS, then swapping assemblies is allowed (GCR/ITCS 17.1.4.C)

The 1986-1991 cars (S4 and S5) are listed on the same line, thus these RX-7 drivers are perfectly legal to swap in the S5 engine into the S4 car (or vice versa) and pick their favorite intake system (complete) to run it with. It would not be legal to choose just the S4 or S5 AFM and bolt that individual piece onto the other manifold (for example). It would also not be legal to "cherry-pick" the best rotors, seals, eccentric shaft, housings, etc and make an engine assembly that did not exist from the factory.

Since ECUs are free (in the context of this conversation) is it irrelevant. As long as they can graft the ECU of their choice using an unmodified wiring harness and ECU housing they're free to do what they wish. Grafting a different AFM, which would require modification of the wiring harness, is illegal, however swapping over the entire unmodified wiring harness to accomodate it would not be.

If the GTU is covered by this ITCS line, then swapping in the entire tranny is legal, but swapping in your preferred 5th gear (only) is not.

This is not a commentary on what they're doing, because I don't know. Simply referencing and clarifying the rules. - GA

Very interesting,
I heard from 3 different drivers that the cars they were running at the ARRC were not the orignal motors or frames that came with the car.
I am not sure but switching from an ITA car to an ITB car surely ain't legal.

It depends what kind of car - and what they meant - as to whether that is a problem or not. Oddly, even turning an ITA car into an ITB car is OK, if the VIN matches the model on the ITB version spec line.

It would help if we had specific examples.

K

I think I'll start converting my E30 to a Vanos M50. Heck....I'll even add 100lbs of ballest to get me upto E36 weight.