...The next modification is a tricky one that requires the use of a wideband O2
(oxygen) sensor to do properly. Most performance shops that rent dyno time will hook one of these up to your car while you are using the dyno (and if they don't, go elsewhere). The stock ECU (Electronic Control Unit--the computer that controls the engine) is programmed to dump a lot of extra fuel after the boost pressure reaches 12psi to keep the engine safe from detonation. This extra fuel, however, reduces power by lowering combustion temperatures that we can reclaim by "leaning" the air-fuel mixture so that there is a little less fuel and a little more air than the ECU is programmed to deliver. The "best" air-fuel ratio (AFR) to run the 3S-GTE at on pump gas is around 11.5:1. The least expensive way to lean the AFR safely is to get an adjustable fuel pressure regulator, an inexpensive fuel pressure gauge and a fuel computer such as the S-AFC. Some performance shops will tell you that you only need an S-AFC, but the safest combination is to use all three. Install both the fuel pressure regulator and the S-AFC. Set the S-AFC to zero adjustment across the board and adjust the base fuel pressure to 35psi (base fuel pressure is the pressure when the fuel pump is running but the engine is not, insert a paper clip in your diagnostic connector between +B and FP to produce this condition). Take the car to a dyno and hook a wideband O2 meter to it. Readjust the base fuel pressure to 30psi and add about 10% fuel at every point in the RPM range. Do a pull on the dyno and print out the AFR chart. It should start at around 14.5:1 and quickly drop to near 10.0:1 or even lower. Use the S-AFC to take out a little fuel in the ranges above 3500 RPMs where the AFR is under 11.5:1 but don't go under the stock (0%) level. When you (or the tuner) is finished, you should be at or close to 11.5:1 AFR under high boost and you should have picked up another 10-15rwhp to get you in the 240-245rwhp range. This is around 300 horsepower at the flywheel, which is 50% more power than you get out of the stock 3S-GTE. Not bad for a $1000-$2000 dollar total investment so far.On this web page if you'd want to read more.
...http://www.tunemytoyota.com/forum/showt ... p?p=118351
I've got a fuel pressure regulator on the car, it's been there since I bought it, is it a good idea to buy an apexi safc and control the afr, or am I better just getting an ecu? I'm thinking it'd be much cheaper with the same results using the safc no?
