Sorry for not posting for a while. I'm not a regular here.
The reason for the miata donor is the SCCA's deep understanding of the miata. The Spec Miata class is super popular and highly contentious. The SCCA has developed a very specific set of rules for the Spec Miata drive line/brakes/suspension/etc. So we could simply apply those rules to a locost/miata.
If we were to open things up to other donors/pieces we would have to get a similar understanding of those motors/trans/diffs/brakes/etc. This simply isn't viable for the number of cars the locost/GTL could field. You'd be amazed at the variation of what might seem like a simple one makde model driveline. Look at the 4age as a wild example. Design revisions in driveline and varying suppliers can create the opportunity to make an engine (or any other piece) that's "more equal" by mixing all the best pieces. The Spec Miata rules have already addressed this and it's taken the better part of a decade to get it right.
If we allow open rules (like the current GTL rules) for a locost in GTL, to keep the playing field level, the locost would either have to weigh around 1900 lbs and use an SIR in the 23-25mm range (thus being like the current generation of GTL cars), or it would have to use a far smaller SIR (guessing 18mm-ish) to make the power to weight ratio comparable with the current generation of GTL cars. Either option be VERY expensive for the locost builder and thus mitigate the reason for doing this in the first place. Like $10k-$20k for a motor. Current GTL motors are fully custom 15:1ish full race motors. Steel cranks, custom rods, custom pistons, Ti valves, custom cams, dry sump, extensive head work, etc. Big big money.
The Spec Miata drive line (about 120hp at the wheels) in a 1400lb locost would be bullet proof, cheap, and great fun. They're already bullet proof in a 2300lb Spec Miata. Removing 900lbs would make them last forever.
I know that the locost community is based on an open and creative approach to car building. And that's awesome.
However, open and racing equals one thing. Expensive. The goal of this exercise would be to provide opportunity to be creative (locost) while still keeping the costs under control (miata).
I know that for most of you who already have projects well underway or completed, this is a let down. But for some folks that can put together a miata powered locost, this could be a great opportunity to race competitively in a top tier SCCA national class for a fraction of the typical cost. And at the end of the day, isn't that what the locost idea is all about?
I've been approached privately by a few of you guys that are interested. My real goal here is to see what the interest level is like. So if this is something you might consider, please contact me at firstname.lastname@example.org
Also, look at some of the various locost series being offered in other countries. They are all similar in that they allow only one drive line and spec things like weight, track, wheelbase, etc.
Thank you again for considering this and helping to shape it.