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Originally Posted by freebeard
Is it due for tires? Go tall and narrow, the RPMs will like it.
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Originally Posted by Miller88
It's geared way lower than that. 5th gear at 45 in 5th gear is close to 2000RPM. 6th gear at 45 is 1600. But it definitely gets less mileage in 6th than 5th at those speeds. At 65 it's almost at 2500 RPM in 6th gear.
It does have some sort of VVT system on it. I should be able to bring up fuel trims, not sure if the car will output AFR or not. And I can check ignition timing. My guess is when cruising at lower speeds in higher gears it just has to pull timing too much.
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Originally Posted by serialk11r
FB25 is dual cam phasing, and it's a low-revving economy engine so it should be tune pretty well from the factory...
Your gearing isn't that short considering the size of the car and the drag, you can try taller tires but I wouldn't expect too much.
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This just doesn't make sense. It's a low revving economy engine that doesn't get good fuel mileage when revving low. If that's true wouldn't putting taller tires just make it worse?
Timing advance becomes less important at low revs and higher loads (e.g. going 45mph in 6th gear). The flame is faster and the piston is slower in that case. So unless your timing is retarding below 7-10° BTDC or so I don't see how it would affect fuel mileage that much. Timing advance makes up for slower flames and faster pistons.
Have you done a compression test recently? Maybe you have too much blowby. ??