custom ring and pinion questions for sti R180 torsen LSD

[Ivemadeahugemistake]

Hello everyone, I am new to the forum but have been lurking for a few years and reading as much as humanly possible.

 

I have been working on a Subaru STI R180(3.9 ratio) for my ld28 240Z project and came across this post: http://forums.hybridz.org/topic/36312-turbo-diesel-questions/page-3?do=findComment&comment=289554

stating that his gear ratio is 3.36 is the lowest available for the R180 but more mpg gains could be had if lower ratios existed.

That got me thinking if it is possible to fabricate a 3.13, 2.9 and 2.72 ratio ring and pinion set for the STI torsen R180. The machine shop that I go to for most of my custom fabrication needs has all the equipment to fabricate ring and pinion gears. I have brought them the STI 3.9 ring and pinion as well as the stock 240Z 3.36 ring and pinion as a sample and they told me that they just need the proper specifications to fabricate them.

 

From what understand as the ratio lowers the diameter of the pinion increases and the gaps between ring teeth widen. Would the pinion be too large to fit in the housing? Is this the reason there are no lower ratios?

I assume that a 3.13 set would be a 31 tooth ring and a 10 tooth pinion, a 2.9 set would be a 29 tooth ring and 10 tooth pinion, and a 2.72 would be a 27 tooth ring and 10 tooth pinion. is this correct?

 

Thanks in advanced for any information

[johnc]

If you can get 40mpg with 3.36 ratio (as claimed in the article) you'll never make back the cost of the custom R&P with the hoped for additional fuel savings.

 

Experimenting with a taller tire would be a cheaper way to find out.

[Ivemadeahugemistake]

Hello John,

 

Unfortunately the reverse is true here in the Philippines. A single standard road tire goes for 5,000 to 8,000 PHP (100 to 180 USD) while more performance oriented tires like the Advan AD08 are around 10,000 to 12,000 PHP (220 to 270 USD). The quote I got from the shop to fabricate all three sets of R&Ps is 15,000 PHP for the billets and 10,000 PHP for labor (total of 550 USD).

 

It is cheaper for me to fabricate these parts than to experiment with different tires. Also the engineer who owns the shop owes me one for all the clients I’ve brought him so the deal I get is if the first sets don’t work out all I’ll have to pay for is the billets to do a second attempt.

 

I have to thank you John. If it weren’t for this thread http://forums.hybridz.org/index.php/topic/78123-subaru-wrx-sti-r180-side-axles I wouldn’t even be able to do this. Thank you for designing such quality parts.

[BluDestiny]

If you start making these R&P sets, there may be some people interested in a few sets for high land speed applications or drag racing. A reason for not having lower ratios would be because they were selling this as a quick little car. A lower gear ratio would make it slower to get to speed. 

[Ivemadeahugemistake]

Hello again gents,

So after a bit of google-fu I found this ring and pinion chart:

 

I have highlighted the R&P combinations that I assume would work in an R180, please correct me if I am wrong.

Any input on which will most likely work best would be highly appreciated so I can start on fabrication.

TIA

[NewZed]

From what understand as the ratio lowers the diameter of the pinion increases and the gaps between ring teeth widen. Would the pinion be too large to fit in the housing? Is this the reason there are no lower ratios?

I assume that a 3.13 set would be a 31 tooth ring and a 10 tooth pinion, a 2.9 set would be a 29 tooth ring and 10 tooth pinion, and a 2.72 would be a 27 tooth ring and 10 tooth pinion. is this correct?

 

Thanks in advanced for any information

Your thread is interesting, but probably not for your original reason.  

 

To those who question how an R&P can be cheaper than a set of tires - ivemade is in the region of the world that makes most of the world's stuff..  He just happens to be in the R&P region instead of the tire region.

 

To ivemade - the desirable R&P ratio is determined by the transmission ratios and the tire size.  Most cars come in about 12:1 on first gear x rear ratio (for example 3.062 x 3.9 for a 280ZX), and use about a 24 - 25" tire.  Many early transmissions had very low first gear ratios, like 3.592 (with the 3.36 rear gear - 12.07)  for the early 240Z, but that changed over time to higher first gears, and lower rear gears.  So you need to do the math from first gear to tire size to decide what R&P ratio you want.

 

It's interesting outside of your goal, because you know somebody that can make custom ring and pinion gear sets.  The ring gear size is not changed when the ratios are modified, it's the number of teeth, with the ring gear size kept the same, to fit the housing and differential carrier.  So if your guy really knows what he'd doing, all you need to do is give him a ratio and a ring gear size and he should be able to tell you what he can do, within a certain range, like 27:1, or similar.

 

As I understand things...

 

p.s. my use of terminology could be off.

[jthom5147]

I do not have measurements available but please note that from information reported on this site the ring and pinion combo cannot be swapped between old r180s and the "K" r180s found in the subarus. This is in regards to the inner diameter of the ring gear: 110mm vs 115 mm.

 

See here: http://forums.hybridz.org/topic/50499-differential-cv-lsd-hp-torque-r160-r180-r200-r230-diff-mount-faq/

 

But I'm sure you gearset manufacturer will take that into account during design.

 

Edit: although Google just told me that a newer Xterra came with an r180 with a 3.13 R/P. It looks like a short nose, but might be good as a reference.

Edited June 30, 2015 by jthom5147

[phil.barlow]

To ivemade - have you been successful in getting custom R&P sets made? I would Be interested in a 2.90 R&P set for a long nose R180. Bottom line: need tall gears, don't have room in the wheel well for tall tires. Thanks