Well, that's still not the only solution, you could buy a power FC and tune it for such high compression. make the fuel mixture a bit more rich and you shouldn't detonate. Brash boy also makes some nice ECU upgrades.
You could get an adjustable Fuel Pressure Regulator, and try to enrich the fuel that way, but our fuel systems don't easily accomidate that option. you could go with bigger injectors too, but injector flow rate would have to be properly matched to your setup, plus, you'll probably need a better fuel pump.
True, the factory ECU is of the learning type, but you must realize that if you run those pistons, you'll still have problems, as the factory pistons are 11.5:1 compression, you suddenly change them out for 13:1 pistons, and you're still gonna get knock. There's only so much the ECU can do on it's own, and it won't be able to compensate for the extra squish in the cylinders, when the A/F mixture gets compressed that much, it'll detonate from compression alone, and the ECU can't fix that (since it's a physical change in the piston that causes it). while it may work without modification on 93 octane, you will probably get some knock and a CEL. too bad resistor mods and SAFC modules don't work, this would be an easy solution to the problem.
98+ octane fuel is far more stable, so the fuel won't pre-detonate. this is why your fuel choice is critical with the factory ECU. you could run something like NX Power Booster in a tank of 93 octane to get the same result, but in the end, it'll be just as expensive to fill up your celica.
Your fuel economy shouldn't suffer much, if anything, it'll improve a bit with a higher compression (it's more efficient, and the fuel will burn more completely) where it hurts you is in the pocket, as it will cost more to fill the tank than it did before the swap. fuel consumption rate should stay the same, unless of course, you are using fuel enrichment of some sort, in which case, you will be using more fuel in each combustion cycle to keep the mixture rich.
It basically comes down to two choices, pay more at the pump, or enrich the fuel mixture and increase fuel consumption, either way, it'll cost you more for fuel.
I suppose that's why the pistons are specified "For Racing Purposes only".
It may sound silly, but someone should write Super Steet magazaine, and ask them a tech question regarding these. Say you want to run 13:1 TRD
pistons in your 2ZZGE celica, but don't want to pay out the nose for racing fuel. Tell them the problems with S-AFC and similar units on our cars, and request a solution to the fuel enrichment issue. They actually have some good responses for their Tech Q&A submissions, and I'm sure they could come up with an idea or two.
Also, you could ask the guys at Monkeywrench Racing, they may have some ideas (one being the Power FC)
BTW guys, you probably won't get 20 HP from these pistons alone...
According to the site, the 2ZZ's in japan that showed those gains got the full treatment, including TRD
Flywheel, Header, Exhaust, Air Filter
and the cylinder head was also ported. All these mods were done in-house at TRD
direct shop in Hachiozi city, Tokyo.
The pistons alone, so long as you have a good Intake
and exhaust system, should be good for about 10 HP, more if the engine is tuned for them properly.