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Old 01-25-2011, 09:33 AM   #16 (permalink)
Master EcoModder
Join Date: Jun 2010
Location: Australia
Posts: 253

Delivery 'Boy - '86 Suzuki Mighty Boy
90 day: 37.15 mpg (US)

SkipSwift - '13 Suzuki Swift GL
90 day: 35.44 mpg (US)
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My legacy GT (1st gen wagon) did better than yours... Around 15l/100km around town, 10 on the highway.

Single best 'mod' I did for efficiency was a combination of boost guage and air-fuel ratio meter. Drive at the highest load you can without going into open loop. Normally equates to 0-1 psi below 3000rpm. Scored 40km per tank around town out of that one... Also my boost controller was an adjustable pressure relief valve, i found that open/closed loop depended on throttle and rpm only, not boost pressure. So using my boost controller set to high (not normally considered efficient) it could run up to 4psi (as opposed to 1-2) in closed loop going up hills, more than likely helped being able to run higher boost (and get more power) without using the stupid-rich fue mixtures subaru's are famous for...

Another thing you could try is the parrallel fuel rail mod and get the computer tuned to suit. One of the reasons mose people run them rich is because of the fuel rail setup (two separate rails, with one feed, one relief, and a joiner) creates a pressure differential between the first and last injector in the rail. A sad fact of life with most computers is that you have to tune to suit the worst conditions. So if one cylinder is running lean you have to run the rest rich to make that one ok... And the ignition timing for that cylinder is ideally also different from the rest too (but you can't set it right coz the others will ping). End result is overall richer mixtures and retarded timing without the safety that normally comes with it. Although that is mostly theoretical, subaru's have an alarming tendency to destroy #4 bearings and pistons more than anything other. Manifold design is fine... guess which injector is the last in the line for fuel pressure?

It might sound complicated, but the mod and tuning can be quite simple. Get an aftermarket fuel pressure regulator and a third fuel rail (sides are interchangable, you want to have two rails without the factory regulator). Split the fuel feed line and feed it into both rails, with the regulator after you join the rails together again. This gives you even fuel pressure and a way to adjust your open loop mixures. A potentiometer in the air temp sensor circuit can adjust ignition timing (to a degree, pardon the pun).

Another worthwhile mod may be to fan force your interheater (ok cooler, but you park up after going for a drive, put your hand in the scoop, and tell me that your intercooler is cooling down. Also try tell me that the computer will do something OTHER than add fuel and retard timing to get rid of the pinging when you tromp it. And you can't lie about it...). Again mainly for high loads, but if you enjoy them as much as I did, going faster and using less fuel is a double win.

I measured my intercooler temp after going for a thrash on a cold (6*c) day. Coolant temp in my water-air intercooler was 30*c. Then I fixed the pump and it dropped to 9*c. More power without a fuel consumption hit. Worth a try...
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Leighos (01-27-2011)