Quote:
Originally Posted by Isaac Zachary
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. ??
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Nah, you didn't get what I was getting at. The FB25 has bad efficiency at low speed partially because Subaru just doesn't build very good engines, but it's still a low revving engine.
Because it's a low revving engine, you can't play with the VVT. On my old Scion FR-S with the Subaru FA20 engine, I was able to squeeze 1 extra mpg by setting the intake cam to max retard and retarding the exhaust cam a few degrees to maintain overlap for internal EGR. With a low revving engine and short duration cams, you can't reduce pumping losses effectively with this strategy.
I had the same experience with my FA20 btw, efficiency was abysmal below 1500rpm even after I leaned out the fuel map.