Developing better low range for a Subaru

[Dedman]

I have started this thread as a place to discuss ideas and thoughts on increasing the reduction of the Subaru low range gear set using custom made gears. How far can things be pushed? 1.6:1 1.8:1 2.0:1 this will be discussed here.

 

[Dedman]

Albin's Engineering who were the manufacturers of Scorpion Low ranges.



Scorpion is front (20/22) rear (16/23)


L series is front (19/23) rear (19/25)


Looking at gearbox pictures it looks like there's heaps more room for front reduction, so I don't know why there's so little reduction done there. However I haven't sat done and worked out the torque/stresses going through everything...

Interesting. I was so certain that the L-Series low range was more reduction in the first stage. Either way the 1st stage is where any additional reduction needs to happen. The second stage is already maxed out in my box with the L-Series low.

Calculating torques/stresses is not going to be an easy process as there are a heap of variable and very complex geometries.

When you contacted Albin's Engineering was that 2k to make the scorpion set using their designs or just to fully reverse engineer a gear set?

 

[Dedman]

SF low range:

L-series low range

L-series assembled

L-series casing clearance

L-series 4.44 diff clearance

 

[NachaLuva]

Talk to AllDrive Subaru, they are still working on a 1.59 (or 1.6) low range that is a direct bolt in with 4.11 diffs

 

[Red XS]

2K to make an existing design. NO reverse engineering. Hopefully shopping around will find somewhere cheaper.



Alldrive have been talking about their 1.6 for ever.


The figures are ones I was given. and the ratio matches and to me look like they match your pictures. But would need someone to count teeth to be 100% sure.

 

[Rally]

Needs to be strong enough to handle turbo engines. Clearing lsd’s will extract a compromise

 

[Red XS]

If the custom low range is made to the same strength of OEM's it won't be the part that breaks. It's the small driving gears in 1st, 2nd and reverse that will break. Or the axles, as they have the most torque multiplication going through them. With rally's setup I reckon you could break stuff easily if you were rough while in low range. But seeing how your setup is holding up is reassuring for a lower low range for NA's. Not saying don't put a lower low range in a turbo, just be very careful and never spool while in reverse...


Clearances in Alex's last pic are a lot closer then mine.


What's maxing out the second stage reduction Alex? LSD or ring gear?


So I take it the LSD will be the limit for front reduction too? Need a spare gearbox for measuring purposes lol

 

[Dedman]

Talk to AllDrive Subaru, they are still working on a 1.59 (or 1.6) low range that is a direct bolt in with 4.11 diffs

I have next to no interest in a 1.6:1 kit as I am already running L-series low range.

So after a bit of research today I think these are the tooth counts for the low range gear set

Ratio 1st Stage 2nd Stage
1.19 20/22 25/19
1.44 22/20 25/19
1.59 23/19 25/19


I did some back of the envelope calcs today and if changing only the 1st stage reduction then if the diameter of the larger gear was increased by 10% over the L-series gear you would end up with a 2:1 reduction. 10% is not all that much... If its a 10cm gear (pretty sure its smaller than that) then thats only a 5mm radius increase. If you went for a 1.8:1 reduction then its only a 5% increase in diameter.
Just wish I had taken some pics of the LSD clearance when I had the box apart...

 

[Dedman]

What's maxing out the second stage reduction Alex? LSD or ring gear?

Ring gear with my 4.44 ratio diffs the ring gear is fatter than the 4.11s

So I take it the LSD will be the limit for front reduction too?

The LSD will limit 1st stage reduction. Although pretty sure my diff would allow more reduction than an open diff. A Kaaz can't even run 1.59:1

 

[Rally]

I have wondered why ads went for the 1.6 reduction when they are starting from scratch. Maybe they investigated going more but found they could not.

 

[Dedman]

I have wondered why ads went for the 1.6 reduction when they are starting from scratch. Maybe they investigated going more but found they could not.

I always assumed they just grabbed a L-series or scorpion set and tried to copy it/use it as the starting point. The other possible reason is that perhaps it wont fit with a cusco front LSD if you go any shorter.

Regarding you comments on working with a Turbo the weak points I see are the low range selector hub mounting splines and then the rest of the box. I don't see the low range gears being a weak point on their own.

 

[Rally]

I wanted to put the ads gears in when I did my locker, and I was told they were being tested to make sure they were strong enough. I was led to believe they would be ready around Christmas. I am glad I didn’t wait. Anyway, my point is if they are testing them is there a concern that actual steel they are using good enough

 

[Red XS]

Another concern Albin's/Scorpion mentioned is greater reduction will be harder to shift on the fly as greater difference in rotation speeds. 1.58 was their idea of the lowest you can go while being easy to shift. 4wd's usually stop when shifting into their 2+ reduction low ranges.

 

[El_Freddo]

If you're going to do this do it properly - so that it can be used on single range AWD boxes and have a market in the US too.

I'm happy to share this idea as I've got no way to make it happen from a money/time/skills point of view So hopefully you can make something of it, but it probably won't be cheap as it requires a new housing to be created.

My idea is to slot a high/low range setup between the centre diff and the splines of the driving gears and pinion shaft. It will require an extension of the pinion shaft to be created - I don't know if a splined section could work to make a "two piece" pinion shaft that then slots into the centre diff to drive the pinion shaft. This second piece of the pinion shaft in this setup is no more than a spacer for the high/low range to sit over.

Some sort of device to scoop oil into the bearings of the pinion shaft may be needed. With this setup the pinion shaft will be rotating at a different speed to the gearset lower shaft. So long as the bearings in there are good this system will work well.

The high/low range setup would be much like the L series setup - just beefed up to take the forces from the drive gears before power is then passed onto the centre diff.

This idea would have a pre assembled housing with the low range etc so that this is literally a bolt in mod with supporting mods such as modified tail shaft and selector.

One other issue I keep over looking is how to make the gear selector arm work - extending it would need a different angle which wouldn't work with the existing setup in the centre diff housing.

Also by having this setup there could be a selection of different low range options or with a bit more work a locking centre diff too. Coupled with our preexisting low range we should have some good crawlers - next stop is sorting strong driveshafts - maybe.

That's the idea - it would fit on turbo, single range and dual range gearboxes...

I can draw up a diagram if it helps

Cheers

Bennie

 

[Rally]

If you do that the price will surely be so high no one can afford it.

 

[El_Freddo]

If you do that the price will surely be so high no one can afford it.

I see only two other alternatives:

1) put up with what we already have or smash 1st/2nd with a lower low range.

2) buy a "real" 4wd... But we wouldn't be here if we wanted that option in the first place.

Cheers

Bennie

 

[scalman]

so subaru needs lower range ? would it be more capable with same power ? not brake from too low gears ? does it really needs it ?

 

[NachaLuva]

Another concern Albin's/Scorpion mentioned is greater reduction will be harder to shift on the fly as greater difference in rotation speeds.

I really don't care if I have to stop to select LR if it gives me a better ratio :biggrin:

I see only two other alternatives:
1) put up with what we already have or smash 1st/2nd with a lower low range.
2) buy a "real" 4wd... But we wouldn't be here if we wanted that option in the first place.

2) is not an option lol :lol:
1) can be mitigated with careful driving

so subaru needs lower range ? does it really needs it ?

It doesn't need it, but will be a big advantage on very steep or very rocky tracks

 

[Rally]

When I was towing my trailer in bendtethra with the 1.19 low range, I got stuck half way up because of the load, gearing and lack of torque. Maybe with the 1.446 low range I might have been ok. I doubt a 2 litre, even with a 1.6 low range, would have got out either. For me, the combination of 2.5 turbo and 1.446 is so much better, but even so I am a bit like Oliver, I want more. I have seen how much a 2 litre SF struggles, so better gearing should be a real improvement

 

[scalman]

well for towing then i guess 3rd gen outbacks 3.0R with 250hp are just fine. plus auto gives you kinda low range capabilities.
i found so lack of power when i was driving in Austria up to Alps mountains. i was barely moving on 1-2 gears i think, and all other cars was just passing me like it was nothing. must be my catalyst O2 sensor was making all worse too.