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I don't spend much time trying to figure out how to improve fuel economy. I spend my time trying to figure out how to make more power. I would expect worse, not better, fuel economy from changing the fuel pressure regulator. The injectors perform fine with the stock pressure. If you want to play, salvage a regulator from a 7/9 series Turbo. It is 3 bar or 44 psi and yours is 2.7 bar. You will have 10% more fuel pressure. What I think will happen is that the 02 sensor will tell the computer to allow less fuel to counter the higher pressure. 10% more pressure is probably only 3% more fuel. If your injectors are more than 5 years old or have more than 50,000 miles, they may benefit from being cleaned and balanced. RC Engineering and Marren Motorsports do this service.
An improved exhaust can help fuel economy. Synthetic oil can, also. Use it everywhere. Power steering, transmission, engine, rear end. An underdrive crank pulley from MVP can also improve power and fuel economy by spinning accessories slower and reducing drag on the crank.
Generally, though, higher performance does not produce better fuel economy. And consider what you would have to pay for each of these modifications. Lets say you spend $1000 on parts that should improve performance and economy and you end up getting 1 mpg better. You go from 24 to 25. It is going to take a long time to recoup that $1000 in fuel savings. You really need savings on the order of 10%. Every now and then people post the mileage they get. Some people with non turbo B230F get 30 mpg on the highway even with automatic transmissions. Most people seem to get more like 25 mpg. City seems to be about 30% worse mpg.
One of the best changes for mpg, and, arguably, performance, is to a manual transmission. One of the next best changes is to a higher rear end ratio (but this hurts performance).
Philip Bradley
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