3.727 LSD differential swap

[84FordMan]

If you follow me on Facebook you may have already seen this.

Yesterday I took delivery of a 3.727:1 LSD differential assembly out of a 2013-2014 Genesis Coupe 2.0T MT

The Coupe and Sedan share both the same differential housing and the same guibo (Or driveshaft flex disc if you will). The only variance being what's used inside the housing. My 4.6 came with a 3.13 non-LSD differential. Different years and engines have different gearing (3.538, 3.727, 3.909), but I believe we have all come to the conclusion none of the first gens came with an LSD?

The Coupe and Sedan also use the same TCS/ESC hardware, but the Sedan has a bit more intuitive programming when it comes to power/throttle cut. So I expect no issues out of the electronic nannies. Quite excited to see how much difference in acceleration/feel there will be going from 3.13 to 3.727.

The differential will go in the car within the next few weeks.

 

[daviderle]

Exciting times! I can't wait to see how this unique monster will turn out? Other than possibly serving as the template for the 'N division', it should be the fastest road worthy Genesis anywhere in the world.

With all the planned upgrades in place and If I am a betting man, I would speculate that the 0-60 would be in the low 4s and the quarter mile somewhere in high 11...

Remarkable project! keep up the good work...

 

[206rspec]

This would work on the 5.0 as well? Not sure if they differ from the 4.6?

 

[dmitriylm]

Same deal with the 5.0's. The 5.0 diff already has higher gearing though.

 

[dmitriylm]

With the 3.727's do you know the impact on acceleration and cruising rpms? How much faster will the car be? Gas mileage should take a hit right?

 

[daviderle]

Gas mileage should take a hit right?

They are going to bolt on a super charger as part of this project, therefore, one would speculate that gas mileage is pretty much not a concern with the new setup!

 

[dmitriylm]

They are going to bolt on a super charger as part of this project, therefore, one would speculate that gas mileage is pretty much not a concern with the new setup!

Haha, I understand that for a supercharged build it might not matter but I'm still curious of the benefit on a naturally aspirated 4.6. A bump in acceleration plus the mechanical lsd sound great if the impact on mileage isn't significant.

 

[206rspec]

whats the ratio on the 5.0?

 

[dmitriylm]

whats the ratio on the 5.0?

I heard the 5.0 is 3.90 which explains why its so much faster than the 4.6 aside from any power difference.

 

[chrev]

Now i'm wondering if the 5.0 dif will work on my 4.6.

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[84FordMan]

I have done some more research and here is what I have found:

- The TCM is not a Hyundai part, it is a ZF (In the case the Tau with the 6-speed, Lambdas had an Aisin-sourced transmission) part. Hyundai is locked out from making changes to gear ratio.

- This is the crutch of the issue, the input speed sensor measures engine RPM, the output speed sensor measures driveshaft RPM, the rear wheel speed sensors measure actual wheel speed. The TCM takes all this data and the fixed data point of gear ratio, it knows exactly at X RPM, in X gear, wheels should be at X speed. Changing the gear ratio without addressing the TCM, will cause ISS/OSS DTCs to be thrown and the transmission will most likely go in limp mode.

So with that being said, I will just be transferring the LSD over into my existing carrier. I will still keep the 3.727 ring and pinion for a later install, because the TCM will be cracked down the road.

 

[84FordMan]

Final update:

Working with another guy dismantling a 2009 4.6, we have discovered something.

The Hyundai Torsen T2 limited slip differential will not bolt up in the Sedan carrier, mainly because the Sedan uses a 7.25" ring gear and the Coupe uses a 6.75" ring gear.

He is working to see if Quaife, Torsen or OS Giken have an LSD that will fit inside the Sedan housing with it's larger ring gear.

The larger ring gear of the Sedan also means the differential is capable of supporting more torque than the Coupe (to that end, I have seen Coupes running nearly 400 WTQ on the stock diff with zero issues).

And to confirm...

The 4.6 Sedan differential is open, not limited slip.

 

[daviderle]

Thank you for finally putting the 8 year speculation to bed, once for all.

 

[84FordMan]

It also explains why somewhere around 10MY or 11MY that Hyundai stopped putting the full differential ID on the tag and started just putting the gear ratio.

 

[Joe29365]

Very good info. What is your name on Facebook so I can send you a Friend request 84FordMan?

 

[84FordMan]

Very good info. What is your name on Facebook so I can send you a Friend request 84FordMan?

Yes you may.

Edward J McIntosh III

 

[Rey]

Do some figuring: Going to a lower numerical rear in a general sense has the most effect on first gear launch. Acceleration from any fixed speed is dependent on rpm in the particular gear, so basically a lower rear end ratio simply means you do have to downshift to obtain the same rate of acceleration.
You will be pulling more rpm in top gear, which means lesser gas mileage.
Consider that Hyundai programs some heavy torque management (limitation) in first gear by reason of the transmission ECU. So, unless you are able to "defeat" this torque management you may well still experience that first gear "bog" we know so well
I have a 3.73 rear in my Cadillac CTS-V. It was a stick and topped out at about 45 mph in first. Went to a 3.23 with first gear topping at 55 mph. This made first gear more useful to me.

 

[84FordMan]

It's more than just that, the final drive ratio is flashed into the Mechatronic unit and even the GDS cannot change it. Now it may be like MB's 7G transmission where a virgin unit can be programmed with the ratio you desire, but no one has come up with the cash to find that out (Last price check I did was about $2,500).

Even if you swap the ratio from another Genesis Sedan it will still throw fault codes and put the transmission in limp mode.

 

[chrev]

Anyone know of any LSD options for the 2011 4.6?

 

[84FordMan]

Anyone know of any LSD options for the 2011 4.6?

None as of yet. The ring gear size is slightly larger in the Sedan than it is in the Coupe. We will need to find the bolt spacing/pattern of the ring gear and the spline count of the axles, with that information we may be able to find an existing unit in Torsen or Quaife's product line.