gas mileage - EJ22 with 3.7 or 4.11?

[baccaruda]

My wagon runs an EJ22 in front of an RX 3.7 5MT tranny.

I'm considering swapping in a Legacy 4.11 5MT transmission instead, as I don't really need the RX dual range, and I was thinking I might get better gas mileage - since the EJ22 has such great low-end torque, I was thinking that it wouldn't be hampered accelerating through the steeper gearing of a 4.11 and that way I could run the engine at lower RPMs than with the 3.7.

If it matters, the car's tires are 215/75-R 15.

 

 

Whatchathink????

[bratsrus1]

Hey Andy This is Jerry, the 3.70 gears take less RPM than the 4.11 gears for the same speed. So if you are going 60 mph and have 3.70 gears your tach will be reading 3 grand. If you change to 4.11 gears at 60 mph your tach will read some where about 38 hundred you will be turning more rpm's but it will take less torque to push the car most likey better gas mileage because it will be like always going down hill on the flats. Thanks Jerry

[idosubaru]

super annoying for highway traveling. the XT6's have this "disease". the manuals run way more for the same speed compared to the autos - much quieter and nicer on the highway.

[Numbchux]

Hey Andy This is Jerry, the 3.70 gears take less RPM than the 4.11 gears for the same speed. So if you are going 60 mph and have 3.70 gears your tach will be reading 3 grand. If you change to 4.11 gears at 60 mph your tach will read some where about 38 hundred you will be turning more rpm's but it will take less torque to push the car most likey better gas mileage because it will be like always going down hill on the flats. Thanks Jerry

 

that would be true, were the 1-5 gears the same.

 

unfortunately, the EA82t trannies (not just the RX D/R versions) got such low gears, that despite the substantially taller axle ratio, they still turn noticeably higher rpms in 5th.

 

 

 

hard to say whether the mileage would change. as lower rpm does not directly translate to higher mileage. BUT, you'd definitely see lower rpm with N/A gears (IMHO the XT6 trans would be the perfect bolt-in solution. same 1-5 gears as the 4.111, but with a 3.9 axle ratio, still has the fully lockable center diff, and won't require driveshaft or linkage modifications to work.)

[Subarutex]

EA is ************, throw an EJ box in there.

 

Grab all the EJ linkage, I can show you how to make it look NICE.

[monstaru]

i'm with tex,cause i want your tranny sucka!!!!!!!

[baccaruda]

heheh. if i pull the RX box out of the wagon I'll very possibly put it into the EA81T coupe, which you should buy from me.

 

Thanks for the inputs, guys. I'll look into the individual gearboxes' final drive ratios for a while, I guess.

[TomRhere]

You got some positive and negative going as far as fuel economy.

 

The 4.11 will let engine respond to throttle input faster than the 3.70 will, that's a positive.

 

The 4.11 will off-set some of the power loss of turning those larger tires, that's a positive.

 

As Jerry said, your engine will run at higher RPM with the 4.11 for the same speed as it would with the 3.70, that's a negative.

 

Up to a point, a larger than stock tire can slightly increase mileage, but after you cross that point, a to large of tire decreases mileage. Some positive, some negative there.

 

You may not actually see any change in your fuel mileage under some driving conditions. But on others, like a long highway trip, it may drop. It's all in the positive/negaive and how it all adds up at that time.

[idosubaru]

Up to a point, a larger than stock tire can slightly increase mileage.

yes. i've done this on an XT6 and monitored the change. i've upgraded to 16" (XT6 stock 14") and they defintiely get a few more miles per gallon on interstate driving. keeping in mind that skinnier tires are better than wide for gas mileage. i forget the exact numbers, but i'm thinking 2-3 mpg better. this would certainly be easier than swapping front diffs.

 

some people on another thread mentioned that gear ratio does not affect gas mileage, or not in the way of "lesser RPM's=better mpg's". i disagree but not quantitatively.

[Numbchux]

As Jerry said, your engine will run at higher RPM with the 4.11 for the same speed as it would with the 3.70, that's a negative.

 

as I said above. this is only true if the only difference between the RX trans and EJ trans was the axle ratio. but that's not the case. the EA82t's got much shorter 1-5 gears (5th in the RX case is 0.871, whereas 5th in the legacy 4.111 case is 0.780), so despite the drastic change in axle ratio, the 4.111 trans will actually result in lower rpm's on the highway. but they got the same first gear, so 1st hi in the RX case is taller than 1st in the legacy case.

 

 

gary, an upgrade from a 14" wheel to a 16" wheel is entirely independent of the point that Tom was making about tire size. while using a larger wheel with the same outer diameter of the tire will usually result in less rotating mass and therefore better mpg (probably what you're experiencing), baccaruda's wagon is lifted, and running substantially taller tires, which has a completely different effect on the mileage.

 

also, lower rpm's does not necessarily mean better mileage. obviously cruising at 6k rpms in 3rd is going to be worse than cruising at 3400 in 5th (both are about 77 mph in a 4.111 5MT legacy).

 

BUT, similarly, shifting into 5th, and lugging along at 27mph turning 1200 rpms, the engine is going to be working very hard, and getting much worse mileage than if you'd stayed in 3rd and been turning 2100

 

 

 

there's a sweet spot. and the EA82t 0.871 5th gear is far to short to find that sweet spot with the EJ22 (unless you spend a lot of time at 50-55mph, which is about 2500 rpms)

 

but, I'm also not a fan of the EA82 N/A and EJ gears without a low range. just too much space between the gears for city driving.

 

of course, there is no way to get the taller 5th, dual range, and FT4WD/AWD without making a hybrid trans....

[baccaruda]

I usually do 65ish on the freeway in 5HI. 5LO feels luggy.

When I hit the onramp, I can easily accelerate to cruising speed in 3rd and then skip 4th entirely and choose 5th for cruising. The EJ22 pulls rather nicely in the upper half of its powerband.

Unfortunately, I've not yet gotten the tach to work (digidash). I have the correct wire (black with blue) connected to the dash from the ECU but it just reads 0. I'm planning to convert the dash to analog soonish so maybe that'll help.