Is there a rear differential gear available for my '87 that's higher than 3.7? What other vehicles use the same diff?

 

With the price of regular gasoline sitting at US$3.85/gallon, I want to continue my quest for better mileage.

I believe the answer to that would be no. Unless the R-180 was available in a lower numeric/higher gear. (but then you're into $$ for custom work to get it in).

What kind of mileage are you getting (or L/100km)?

Check out a SVX diff...

These differentials were also used in Datsuns, and the larger ring-gear units (R180 and R200) were used in Datsuns/Nissans.

 

The R180, a direct bolt in replacement in my Datsun 510 for its original R160, came in a 3.364 ratio. You may need to play a little with the axle stubs for Subaru use, but there should be info here for that.

 

A useful guide to Datsun/Nissan diffs and their ratios is at:

http://www.geocities.com/inlinestroker/ratio.html

SVX came with a 3.545 (or was it 3.454?) LSD rear diff. The driveshaft would prboably fit, but iirc, the SVX had its own axles, so you would need to do some custom axles.

the SVX has the only higher final drive ratio, but like mentioned above it has different axles. it would be a very very small difference in gas mileage anyway. getting different tires is probably a much better alternative - skinnier and taller = better mileage. tire compound makes a difference to but harder to compare.

SVX came with a 3.545 (or was it 3.454?) LSD rear diff. The driveshaft would prboably fit, but iirc, the SVX had its own axles, so you would need to do some custom axles.

3.545 is correct. However, if one changes rear diff's, they must also change transmissions. And for those who don't know, SVX transmissions suck.

they must also change transmissions.

not true, you can also run in RWD. which the title of this post suggests he is doing.

Yeah, you can use any ratio on the rear diff you want if you run in RWD.

Right now my mileage isn't great - maybe around 20mpg. It was better this spring, but they've recently changed all the regular and mid-grade pumps to ethanol-blended fuel in my city (9% ethanol blend), and that's negatively affected my mileage. It was 23-24 mpg before. I could tune my engine/carb for ethanol, but then I'll have problems if I ever travel somewhere that doesn't use ethanol. Premium fuel doesn't have ethanol, but it costs over 10% more.

 

I spend about $250-$300 per month on fuel right now, so a 10% improvement in mileage will give me $25/month in my pocket for other stuff I'd rather be buying.

 

I'm planning a transmission swap this summer (going to a d/r 5-sp), and I'm also going to put an spfi block into the car. If I don't run out of time, I might even swap over to an spfi system instead of the carb. Those things will give me the biggest improvment.

 

If I can take an R180 diff and swap stubs, it might give me the gears I'd want. I noticed that one of the available ratios is 3.36:1 - about 16% taller than the 3.9:1 that I have now. That would drop my highway cruising revs from 3000 to around 2600.

 

Skinnier tires are something I'll be eventually doing, but I want to use up my current tires first.

A properly tuned SPFI system would indeed be a big improvement. But then, if you set up your carb for specific driving situation (eg - level highway cruise) you could do nearly as well. I do like the SPFI system.

 

When I put the R180 in my 510, it really made a difference in my cruise. With my Z20 engine and 5-speed, it will cruise nicely at 80mph with less RPMs than it used to (with L16/4spd/origR160) at 55. At 55/60, the engine is purring at a nice, relaxed RPM. Did have a little problem with the swap, as I didn't grab enough parts (axle pieces), and ended up with a mishmash of axles left to right. But that was bad planning on my part, and PAP recycling cars too quickly.

 

IMHO, a 16% ratio change could equate to a 10-15% mileage improvement. Much of the fuel consumption at freeway cruise is due to just frictional losses due to engine RPM (and to some extent load factor).

an ideal set up would be to own two cars. a FWD XT is capable of 40+ mpg and have you other for the dual range fun.

I'm with Gary. A FWD 4cyl XT is the ideal gas meiser 80s Subaru out there. Low drag, low weight, 4 cylinders, mpfi, fwd, etc, all make it an ideal gas saver. Or, get a 4WD XT and put it in RWD w/ 3.7 on the rearend.

Is this in the hatch? Seems pretty low MPG. My '83 got 26 US/ 31 IMP MPG on the highway cruising 70-75MPH (trip to Oregon). 300,000 km on engine/carb, decent tuneup, rebuilt disty, new plugs, new fuel filter, valves actually could have used an adjustment, one of the last good Accel coils. Plus, I was running Pugs at the time with 195/60/14 's and carrying a load of camping gear and tools.

 

What is the state of tune (recent parts) on your car?

EDIT: Yes, it's the hatch, but an EA-82 HB.

 

The car is tuned up pretty well, but like I mentioned before, the local switch to ethanol-blended fuel hurt my mileage. I was around 24mpg before it, and now I'm down to 20ish. My wife's car (a 92 Loyale) was able to compensate better, and her mileage only dipped a little. I could tune my car and re-jet the carb for ethanol-blended fuel, but then it would be really out-of-tune whenever I travel somewhere that doesn't have an ethanol blend.

 

One other thing that affects my mileage is that about 25% of my driving is on dirt/gravel roads. This year has been soft and wet. I rarely ever use 4wd because the Subaru gets such good traction, even without it.

 

Just thinking about it, I might just go ahead and re-tune for ethanol fuel. I don't take the car out of town very often. Also, I have a roof rack on the car that is probably taking 1-2mpg from the car's potential. I like how it looks, but it might just have to go...

 

Anyways, I'll have to keep my eyes open for an R180 diff at the local JY.

i would do a spfi swap if you have the funds. any sort of fuel injection is going to get as good or better mileage than a carb. but if you really are considering a spfi swap, you might as well fork over the extra bones for a EJ18 or EJ22 swap, hard to justify to the woman, but worth it. id go EJ18 for the swap if i were you.

 

you have to strip down a wire harness for either of those swaps so you might as well strip the one with the most power......im biased but thats besides the point. with an EJ22 you would get about 26 mpg highway only. with a EJ18, you could get 30. but if you want it simple and easy, grab a 3.70 rear diff(lsd or not) and throw it in there. you might see a marginal boost in mileage but you drive on gravel roads so i doubt it.

 

most gas stations switch to ethanol blend in the winter. but you should be fine as long as you dont get too crazy with the timing. dont re-jet your carb or anything like that.

 

~Josh~

Maybe do a SPFI swap. My SPFI wagon gets 32mpg w mostly highway driving. That's running regular gas, at an altitude of ~6500 feet, and with a 10% Ethanol blend (virtually all Colorado gas stations use 10% ethanol blends...)

Do you have Chevron Over there because they haven't started to use ethanol yet

Our province is transitioning over to ethanol-blended gasoline right now. With the way it is working out, all of the regular and mid-grade pumps in my city, regardless of brand, have 9% ethanol in them. Basically, as long as I use this as car locally, I'm guaranteed to be driving with 9% ethanol in the tank. For absolutely best performance, I could (but probably won't) tune my car specifically for the blended fuel.

 

An spfi swap is a lot cheaper for me than an EJ swap. I already have an '88 DL for a free parts car. It would take me forever and cost a ton to find an EJ18 or EJ22 that I could swap in.

 

I took the roof rack off tonight. I'll see over the next couple of tanks how much it changes the mileage. I also cleaned all of the non-essential tools and spare parts out of the back of the car.

 

Anyways, back to the original topic - Which vehicles have R180 diffs in them?

...

Anyways, back to the original topic - Which vehicles have R180 diffs in them?

Datsuns/Nissans, mostly "Z"s. Did you check out the link that I posted on the first page?

Just swap the RING AND PINION and dont bother with the diff swap.

 

any R160 R&P will fit in your stock R160. Find a WRX or SVX rear diff, and use that R&P. Both of those are 3.545.

Datsuns/Nissans, mostly "Z"s. Did you check out the link that I posted on the first page?

 

It was blocked from work. I just looked at it now from home - excellent!

 

The odds of finding an SVX or WRX here are close to zero - I'll have better luck finding a Z, and playing around with axle stubs.

EDIT: Yes, it's the hatch, but an EA-82 HB.

 

 

Is this the car in your sig? It's an OHC engine? Maybe try a Weber. Properly tuned, they can give you better mileage as well as more power.

Have you considered using waste oil in a diesel car? Free fuel.

We are running 10% ethanol in Vancouver, with only a minor drop in mileage. My brother just put a single range 4WD tranny and diff from an XT into an '87 sport coupe SPFI. The ratio is 3.7, and with stock tires, he is getting in excess of 40 MPG. Granted, he does a large %age of highway driving, (using cruise), and tries to keep it below 70 MPH (110 kmph). It is fine out on the highway, but around town it does feel like you are starting out in second gear, about the same as running 15" tires.

There are many factors affecting mileage, driving habits, engine tune, dragging brakes etc.. I deal mostly with wagons, and a 2WD 5sp will get high 40's, a 4WD 5sp will get around 40, and autos will get low 30's. 3.9 does seem to be the best fit for the non-turbo cars.

If you are still getting poor mileage, ease up on the pedal or look for the gas leak.