I too live in the Bay Area, Sunnyvale to be exact, and tried almost all of the gas stations in my area, sending logs to Halim. This was just over a year ago if I remember correctly.
There are 5 oil refineries in the Bay Area, in order of size (No. of barrels processed per day):
- Chevron
- Marathon
- Shell
- Valero
- Philips 66
Unfortunately there is no guarantee that a gas station you go to uses the gas from their own refinery and even if there were, the big difference between gas is only additives, and these do not affect octane in any significant way.
At that time I tried Chevron, Arco (Marathon), Shell, Valero, 76 (Philips), and Costco stations. They all performed identically, and identically bad.
I tried 1 step colder plugs, and they're an improvement, but nothing to write home about. I probably wouldn't bother if I were doing this again.
I experimented with mixing E85 to create E blends on the OTS 91 map (ACN 91 OTS map wasn't available at the time), and found that E20 improved things to just about acceptable with this map, but really a little more octane (E value) would have been better. When I went over E20 my HPFP ran out of pressure but that's an option if you don't mind blending for every tank.
I believe in CA we're left with four options to this problem:
- WMI (the route I took)
- Upgraded HPFP to handle higher E blends
- Blending race gas to achieve higher octane
- Use octane boosters like Boostane
Going the HPFP route and an E30 blend will allow you to run the (regular non ACN) 91 OTS map safely (do not use the E30 map because this assumes a good base fuel before the Ethanol is added; we don't have that luxury!), but probably not the 93 OTS map. You could add more Ethanol than E30 with something like a stage 2 HPFP, but then you might run the risk of damaging the top end of the engine because the oil layer of the cylinder and valve train can be cleaned off if there is too much ethanol. You can use a top end lubricant to help with this, but then that's something else again that you need to do.
A good, progressive WMI kit will allow you to run the 93 OTS map safely because it boosts octane, fuelling and lowers IATs. It's also really cheap for a daily driver. 1 gallon of 50:50 water:methanol lasts for about 2 tanks on the street (would be used much faster on track), and 5 gallons of Methanol costs bout $35 - Less than $2 per tank for street driving.
Blending race gas is a good option, but it's very expensive and it's difficult to find race gas (though certainly not impossible, I know of a few stations in the Bay Area). One thing to keep in mind is that octane doesn't mix linearly. What I mean by that is that if you mix 1 gallon of 91 AKI with 1 gallon of 101, you don't necessarily end up with 96. When I tried this I got closer to a 93 AKI result with 50:50 race gas, and that's an expensive proposition for a daily driver.
Octane boosters have been used effectively by some users on this forum, but I didn't want to go that route. It's in between the price of WMI and Race Gas blending, but it turns the inside of your engine, turbo and exhaust system orange, and the long term consequences of that concerned me.