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Summary: The LC500 rear differential has a final drive (not sure if this is the correct term, i am borrowing it from the motorcycle world) ratio of 2.94. The LC500h has a shorter final ratio, at 3.13. Why do you want a shorter ratio? Shorter gears mean more torque at every rpm, therefore more in-gear acceleration at the cost of top speed, at least in theory. There are multiple differentials that fit the LC500 including I believe some from the LS500 which all have the same exterior housings and are similarly plug and play, with different gear ratios (read the above links for more details on those).
However, to the best of my knowledge, if you wish to swap the entire differential (a much simpler and idiot proof job, as opposed to opening it up and swapping individual internal gears) and you want the Torsen LSD included, then you will need to use the one from the LC500h. Which one? Here are the part numbers:
41110-11050 - This is the entire differential from the LC500h including the Torsen LSD. This is a single self contained unit and all you need at the princely sum of about $4k USD. The drive shaft and axle seals are included with the package preinstalled but in case you need replacements, the part numbers for the seals are: 90311-47031 and 90311-47032
Installation is pretty straightforward, the exhaust muffler section comes off, the driveshaft, rear axle, and rear steer module (if you have one) is disconnected and the differential is swapped. Everything goes back in the same way it came out. The LC500h differential housing is completely identical to the LC500. The differential/torsen is completely mechanical, there are no electronic elements to worry about. No error codes, no weird behaviour from the car. Everything feels stock, and works without issue.
Is it faster? Unquestionably. It is far from subtle (but I would stop short of calling it a "night and day" difference). You will notice it the moment you step on the gas pedal the first time the car starts moving: There is a noticeable increase in torque/acceleration. Something I should also make clear: It is much more than something you could ever get from an exhaust and a tune on a naturally aspirated stock engine, which could cost similar amounts of money and compromise reliability, which this mod doesn't. I was trying to think about the best way to express it and my best attempt is that it feels like someone bored out my engine by another 500-800cc, so it feels like a 5.5 or 5.8L engine now. The power increase is across the entire rev range, and the best part of it is how much nicer it pulls from below 2000-4000rpm where this engine can feel a little anemic. At higher revs the power increase is less noticeable (probably because the engine is already producing a lot of power there). The lovely part of the way it feels is not only did I get more 'power', not only did I get it 'everywhere' in the rev range, but I also got a better car for street driving at the same time, which is great. If you would like some numbers I'll quote another forum member who did the mod and took some measurements in the earlier thread:
Originally Posted by anchaf3
Subjectively the car is much livelier and feels quicker. Objectively, the 60mph-100mph has improved. I was averaging 5.5-5.6 seconds now I consistently pull in the 5.2 range in the 60-100mph with my best being 5.15 seconds. As far as 0-60mph, I have had to get creative launching it because it now will break traction so bad with my pilot sport 4s tires. I can consistently pull 0-60 (with a 1 foot roll out) under 4.3 seconds now. The best time being 4.23 seconds. Before I would never break the 4.3 mark, and would usually be around 4.5, Occasionally I would have a dead hook launch with my old set up and get close to 4.3, but that very rare and under perfect conditions and having some luck. Overall it is quicker, no question.
I would like to add to his opinion that I believe the traction control systems on our LC500s are simply too invasive. I did once try to disable TC fully, with fully warm stock dunlop runflat tires on hot tarmac and was able to floor the pedal in first gear and get the car to accelerate smoothly from absolute standstill (without brake boost) with no audible loss of traction (I did not hear any tire squeal or hear the rpm spike from tire spin) even with this new differential. Unfortunately I did not have measuring equipment to measure that run. I did the exact same run next with TC enabled and it was flashing lights and cutting power everywhere so yeah, the TC sucks on our vehicles and is far too conservative
Drawbacks? First of all this is not a cheap mod, but then again this is not a cheap car, and there is no way that spending this kind of money on the car on any other mod(without forced induction) will get you this kind of improvement in performance. So from a bang for the buck perspective, it is still a good deal IMO. There are also cheaper ways to do it if you are so inclined, by swapping out internal gears. But swapping out the entire differential is also a good idea if your LC500 does not come with a Torsen LSD and you want to have one, an added bonus.
Other drawbacks besides cost are a small but noticeable increase in engine braking off throttle, whether or not this will annoy you is highly subjective but not everyone will like it (it annoyed me slightly at first but I adapted after a while and it just feels normal to me now). The issue is slightly exacerbated by the fact that when coasting to a stop, the downshifts on the 10 speed are not the smoothest in the world, you get small changes in the rate of deceleration as you drop down the gears and the increased engine braking does accentuate this a little
Fuel consumption: Doing a 100% apples to apples comparison is difficult. When i first had the differential swapped, my fuel consumption skyrocketed because i was flooring it all over the place lol. Now that things have settled down a bit and I am back to my regular driving style, i would say fuel consumption has gone up by about 5-8%, for the same style of driving
How about top speed? Well on some other cars, you might lose a little, on this car, you lose nothing. The car is limited to 285km/h and the 10 speed is geared to reach that speed in 7th gear (at about 6000rpm). the only difference with this mod is that you will hit 285km/h at a slight higher rpm in 7th gear compared to before. In fact, with the improvement to in-gear acceleration, you will probably hit top speed a lot sooner compared to stock. You do lose a little 'top speed' in each gear due to the shorter gear but if anything it makes the car more fun to drive, especially in manual mode, because you're banging up and down that lovely gearbox even more. (Edit: I was wrong, limited top speed drops to 245km/h. Please read my post below to find out why)
Overall great mod, really happy with it. If you're ok with the cost, and can deal with a little more engine braking (Edit: or you actually spend time driving between 245 and 285km/h)...there really is no reason not to do it
Hope someone finds this useful, shoot me a question if I missed something and I'll try to answer if I can
Looks like the differential assy for the hybrid is available from some OEM parts dealers. looking at the schematics and part numbers it appears to be a direct swap. It might be an expensive swap, but i think it will yield good results.
Really interested in this idea. I swapped from 3.46 to 3.91 in my 06 GTO and it absolutely livened the car up. That's almost the same jump as 2.94 to 3.36
Here is the speed at 7300rpm in gears 1 through 8. I also threw in the speed at 1500rpm in 10th.
Setting the gears up to mesh correctly can be difficult. If the pinion is too far in or out you can end up with a whine or premature wear. If swapping the whole diff is an option that's probably the way to go.
Really interested in this idea. I swapped from 3.46 to 3.91 in my 06 GTO and it absolutely livened the car up. That's almost the same jump as 2.94 to 3.36
Here is the speed at 7300rpm in gears 1 through 8. I also threw in the speed at 1500rpm in 10th.
Setting the gears up to mesh correctly can be difficult. If the pinion is too far in or out you can end up with a whine or premature wear. If swapping the whole diff is an option that's probably the way to go.
So, I bit the bullet. I ordered the entire diff assembly for the hybrid, part #41110-11050. Should be in by the end of the month.
Got my car back today from the mechanic. Diff swap to the 3.357:1 from the hybrid was successful. Still breaking it in, so I haven’t launched it or went WOT yet. But most importantly, no error codes, and the speedometer is reading exactly the same.
From my 30 or so miles I put on it today it is definitely more alive.
I have logged several hard pulls and rolls on my Dragy app with the stock diff, so I’m looking forward to seeing how the new gear ratio affects the 0-60, 1/8th mile, 1/4 mile, 60-100, etc. I think there will be a big difference.
It is accurate. Using my GPS as the standard, the speedometer is 1-2 mph faster than GPS when using the stock 2.94 diff. Using the same GPS device, the speedometer is still only 1-2 mph faster than the GPS reading, when using the 3.357 diff.
Originally Posted by QwkSC
Do you mean the speedo is accurate, or not accurate?
Glad to hear the diff is a straight swap. That's convenient, no need to worry about gear whine or finding a good diff specialist.
It is accurate. Using my GPS as the standard, the speedometer is 1-2 mph faster than GPS when using the stock 2.94 diff. Using the same GPS device, the speedometer is still only 1-2 mph faster than the GPS reading, when using the 3.357 diff.
That's fantastic. If you get a chance to do a 1/4 mile run please keep us updated!
Note though that while the external cases of the differentials are the same between all models, the differential unit itself seems to potentially vary between different gear ratios. Not sure if this is a flange thickness difference or what, but there is the potential that a different differential unit may be required if you change the gearing. Getting the entire assembly like anchaf3 did is an option, but for the LS differentials, LSD wasn't an option, so if you want the 3.615:1 ratio, you'd need to either swap the gears into an LC diff, or swap an LSD into the LS assembly.
41201-59355 and 41301-11040 are the matched set for 3.615:1 with a Torsen LSD. 41201-59355 may fit the 41301-11020 Torsen, but it would need to be checked.
Replacing LC500 torsen diff with LC500h one!
