I think the Personal License Program is one of the best ideas Ron has initiated! Most of us want to modify our own cars, but the cost for doing so with either the certification program or sending in the throttle bodies is prohibitive--especially if you have 5 cars--and tend to buy cars for your progeny!
Just finished grooving car #1, a 1996 3 cylinder Metro with 120K miles. Pre mod = 40-43 MPG. First used the medium bit, as the throttle body bore is pretty small--resulted in more power and small gain in MPG, 46 on the freeway.
Ron advised using the larger bit, did so. Also a) rerouted the small hole that was right in the middle of the groove up higher in the bore, b) plugged the PVC valve with an appropriately sized sheet metal screw and c) capped the throttle body hose ports to the EGR and blocked the EGR ports with a metal sheet. After doing the computer conditioning took a trip of 191 miles on I-5. Took 3.4 gallons, or 56 MPG--although I really nursed it, using a Scangauge. BTW, the Scangauge takes some time in getting used to the groove--first few fillups it consistently read more gas used than it took at the pump. Power is up, too (though power is a relative term for a 3 cylinder engine!). Pre Mod, going up Snoqualmie Pass (east bound), could barely maintain 55 MPH on the steep section just before the summit. Post Mod, 65 was easy.
I've experimented with home-built HHO, and will probably do more in the future, but the problems of leaks, freezing in winter and keeping it filled amounted to a pain. And the gains were nothing compared to the Groove mod--which is such a comparatively simple process--and once done, needs no continual maintenance.
