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Have some somewhat useful anecdotal evidence, despite current condition of my car.
The core engine mods:
Destroked from 2.26 L to 1.99 L
Long custom rods (ratio is 1.92:1 IIRC; I would reduce this to 1.8:1 or so)
High compression pistons (12.3:1)
On the head:
Custom cams, but I don't think they were done properly
Bowl work
Gasket matching and porting on the exhaust side
Others:
Modified stock intake manifold
Tubular exhaust manifold
Larger turbocharger
Larger turboback exhaust
Full E85 for fuel on stock injectors
More info:
The rings that came with the pistons aren't great, and the ringlands might also be damaged due to testing I shouldn't have done for the company that makes the tuning software I use.
Currently, I'm getting better than stock MPG (~25-28) on full E85, while the engine requires two quarts of oil per tank of fuel due to low compression (lots of smoke) so I'm sure it would be even better if I wasn't wasting cylinder pressure.
I think the compression ratio is what really gets the most bang for the buck as far as MPG goes, but if your only choice is to build the engine around the gearing for your transmission and the driving you do, I think you *can* optimize your rod ratio to hit the sweet spot of BMEP VS RPM that way (combined with other mods, of course). Kind of an expensive way to do it, but seems at least feasible.
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