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Old 01-11-2021, 06:04 PM   #11 (permalink)
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Economy plus head gaskets? Plus the boxer engine? Beetle wannabes.

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Old 01-11-2021, 09:02 PM   #12 (permalink)
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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. ??
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.
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Old 01-11-2021, 09:30 PM   #13 (permalink)
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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.
Interesting.

I've never had a Subaru but I've always gotten my best fuel mileage in the 1,000 to 2,000 RPM range, not 2,000 and up range. And that has been the case on a few different vehicles, not just one or two.

I wonder how that would be affected by load, as in pulse and gliding. Would keeping it at up over 2,000RPMs still be more efficient for pulse and gliding than at lower RPMs?
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Old 01-12-2021, 04:15 PM   #14 (permalink)
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I'm not sure if I'd 100% agree with it not being a high revving engine. This seems to love running up to the limiter. Even my old Focus with the Duratec I4 didn't seem to like much past 4500. But this enjoys it.

The FB engine definitely has a larger stroke, less bore and externally plumbed heads so they don't have the head gasket issues.


They did do a good job of putting underbody aero on it so not sure if that would get us too far. When I say it doesn't like lower RPM, it seems to "buck" under moderate acceleration under 1500 as well. The other two I test drove did the same thing.


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I had a 03 Forester X with the 4-speed auto and 2.5L NA engine (4EAT + EJ25) and my best efforts of basic aerowork, tire pressure, and driving speed of 50mph got me 33mpg. Otherwise, mid-high 20's was the best I could do.

I now have a 07 Forester XT with the same auto, but 2.5L turbo (with a few mods) and my best tank so far has been 27MPG doing 60-80mph. I haven't really had a chance to give it further road tripping for better, so tanks are 18-23MPG otherwise.

All this is to say: Good luck! Subarus were built with many things in mind, but economy isn't one of them. (or headgasket life)

I can get low to mid 30s out of it around 55 or so. Even highway trips can net me 29MPG as long as I keep it at 65.


So I think for now I'll do a grille block for winter months at least. Maybe I'll see if I can pick up a set of more eco minded tires. A 215/65-17 set of ecopias or something would be similar diameter but a bit narrower.
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Old 01-12-2021, 04:43 PM   #15 (permalink)
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So I think for now I'll do a grille block for winter months at least. Maybe I'll see if I can pick up a set of more eco minded tires. A 215/65-17 set of ecopias or something would be similar diameter but a bit narrower.
That's what I was going to suggest, a grille block and narrower, but same diameter tires.

Another help could be an engine block heater. I've put 1,500W circulating heaters on my engines. The higher the wattage the better. Even if you plug it in for 15 minutes you get more heat for less electricity because you're not giving it enough time to cool off and heat the environment. Or go for an hour or two to completely heat the engine to operating temps. Or go for a block heater around 700W and throw a 700W space heater into the cabin if it's too cold to drive (you either are cold blooded or you need to defrost your windshield).

This would mainly help if you have short drives, but if you drive at least 5 or 10 miles or more per drive then the benefits are less noticeable. Still, I don't ever warm up my engine before driving: even today when it was -20F (-29C) when I got into my car.
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Old 01-14-2021, 04:10 PM   #16 (permalink)
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I would like a block heater on this car. And i did actually ask the dealer to install one but they didn't do it. Apparently the exhaust manifold on the drivers side has to come off and they didn't want to go through that on a new car.

I think this weekend I should have some time to work on a grille block. Looks like we aren't going to get a very frigid winter this year
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Old 01-14-2021, 06:23 PM   #17 (permalink)
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I would like a block heater on this car. And i did actually ask the dealer to install one but they didn't do it. Apparently the exhaust manifold on the drivers side has to come off and they didn't want to go through that on a new car.

I think this weekend I should have some time to work on a grille block. Looks like we aren't going to get a very frigid winter this year
It sounds like one of those typical 150-300W block heaters. Those help, but don't do much. That's what I got on my Avalon right now. It's a pain because I can leave it plugged in all night long, for hours on end, get in the car and drive to work with the heater off and the engine still won't have reached operating temperatures by then.

I'm not saying a circulating pump heater would be easier to install, but it might, and you get more heating power.

Again, say you have the choice between a 150W block heater and a 1,500W circulating heater. You could plug in the 150W heater for 10 hours and the 1,500W heater for one hour and use the same amount of electricity. But in the end your engine will be far warmer with the circulating block heater.
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Old 01-14-2021, 10:35 PM   #18 (permalink)
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The circulating ones are the ones that go in place of the upper radiator hose? I've seen those but wasn't sure what to think of them. Any suggestions?

Letting the thing warm up definitely kills fuel economy. Normally I wouldn't let it idle for that long, but the high just puts too much wear on all of the clutch components taking off and shifting.
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Old 01-15-2021, 01:15 AM   #19 (permalink)
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The circulating ones are the ones that go in place of the upper radiator hose? I've seen those but wasn't sure what to think of them. Any suggestions?
No, I don't like those. They don't really circulate anything nor heat up the engine. So avoid them.

The kinds I'm talking about are one of two.

One has an electric pump built in. These are more expensive and harder to find. They go on the heater line, assuming you don't have a heater shut-off valve, and pump the water through the heater core and the engine.

The second type, which is much more common, is the "tank" circulating heater. These you splice into a heater/radiator hose that's down low on the engine and then into a heater hose that's up high, avoiding any (already there) valves or thermostats. The cold water feeds into the bottom of the "tank" heater which is mounted as low as possible and the heating element acts like a Percolator and causes hot water to flow up into the top of the engine.

Both of these are mounted to the frame or firewall somewhere. They also can be damaged if you have them plugged in and start the engine, depending on if your water pump pumps in the opposite direction or not. The tank heater also opens a path that lets water bypass the heater core in the cabin to some degree, which may or may not be a problem. On my VW diesel I installed a 120V solenoid valve that would automatically open when I plugged it and the tank heater and then would automatically close when I disconnected it. It worked pretty well.
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Old Yesterday, 01:13 PM   #20 (permalink)
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