GR Yaris Correct ratio 4wd

[Not.a.circuit.pack]

Hey all, I've not seen any posts about it, so hopefully this will be useful for someone.

I've had the Brena Racing correct ratio crownwheel & pinion in for a while now and have to say it's an absolute game changer. Essentially it gets rid of the ~.7% overdrive to the rear wheels. Yes, you loose the "70:30 rear drive", however everyone knows the torque to the rear doesn't turn the GRY into a drift car
What you get here - combined with Syvecs 4wd controller- is the ability to fully lock the rear clutch pack and a full 4wd capability. It was mapped on an uncoupled dyno and the wheel speeds were absolutely spot on. Now this thing launches even better, and it's totally enhanced the handling. If anyone is considering it then get in touch

 

[GottGry]

I've had the Brena Racing correct ratio crownwheel & pinion in for a while now

This is on a convenience pack car with no Torsen-like diffs?

 

[yan.ko]

Toyota part 41201-52010 provides the same. It’s a 41/18-teeth transfer gear kit, matching the ratio of the rear differential.

If you like to go for something stronger, XSHIFT makes very strong 32/14-teeth transfer gear kit (https://www.xshiftgearboxes.com/hypoid-gearsets/toyota-gr-yaris).

Additionally it might be even matched with Kalle Rovanpera 39/17teeth rear diff kit (Toyota 41201-59435), giving GRY super strong equal ratio setup capable of fully locking 4WD (when matched with Syvec or other 4WD cotroller).

 

[Fred]

Toyota part 41201-52010 provides the same. It’s a 41/18-teeth transfer gear kit, matching the ratio of the rear differential.

If you like to go for something stronger, XSHIFT makes very strong 32/14-teeth transfer gear kit (https://www.xshiftgearboxes.com/hypoid-gearsets/toyota-gr-yaris).

Additionally it might be even matched with Kalle Rovanpera 39/17teeth rear diff kit (Toyota 41201-59435), giving GRY super strong equal ratio setup capable of fully locking 4WD (when matched with Syvec or other 4WD cotroller).

View attachment 34743

Hey all, I've not seen any posts about it, so hopefully this will be useful for someone.

I've had the Brena Racing correct ratio crownwheel & pinion in for a while now and have to say it's an absolute game changer. Essentially it gets rid of the ~.7% overdrive to the rear wheels. Yes, you loose the "70:30 rear drive", however everyone knows the torque to the rear doesn't turn the GRY into a drift car
What you get here - combined with Syvecs 4wd controller- is the ability to fully lock the rear clutch pack and a full 4wd capability. It was mapped on an uncoupled dyno and the wheel speeds were absolutely spot on. Now this thing launches even better, and it's totally enhanced the handling. If anyone is considering it then get in touch

The Brena kit is very nice and highest quality, but quite expensive...
Where did you get it from and was it easy to install? Probably you need various shims?

 

[MRA3]

Toyota part 41201-52010 provides the same. It’s a 41/18-teeth transfer gear kit, matching the ratio of the rear differential.

If you like to go for something stronger, XSHIFT makes very strong 32/14-teeth transfer gear kit (https://www.xshiftgearboxes.com/hypoid-gearsets/toyota-gr-yaris).

Additionally it might be even matched with Kalle Rovanpera 39/17teeth rear diff kit (Toyota 41201-59435), giving GRY super strong equal ratio setup capable of fully locking 4WD (when matched with Syvec or other 4WD cotroller).

Don’t they do the same thing? Meaning, 52010 matchs the ratio of the rear by changing the transfer ratio, so it’s all the time 50/50.

If you put Kalle’s 59435, but you keep the transfer gear stock (not sure if this is true in the OG Kalle edition), you achieve the same result 50/50 par distribution, just on a different manner.

What I struggle to understand is, once you have the car 50/50, front rear par distribution. What the itcc or central clutches are for (apart from disconnecting the rear end when using the handbrake)? If anyone can enlighten me on this topic, and how changing the itcc modes can affect driving when already 50/50 via hardware.

 

[Fred]

Don’t they do the same thing? Meaning, 52010 matchs the ratio of the rear by changing the transfer ratio, so it’s all the time 50/50.

If you put Kalle’s 59435, but you keep the transfer gear stock (not sure if this is true in the OG Kalle edition), you achieve the same result 50/50 par distribution, just on a different manner.

What I struggle to understand is, once you have the car 50/50, front rear par distribution. What the itcc or central clutches are for (apart from disconnecting the rear end when using the handbrake)? If anyone can enlighten me on this topic, and how changing the itcc modes can affect driving when already 50/50 via hardware.

This video isn’t an answer to your question but nevertheless interesting!

 

[Fred]

Don’t they do the same thing? Meaning, 52010 matchs the ratio of the rear by changing the transfer ratio, so it’s all the time 50/50.

If you put Kalle’s 59435, but you keep the transfer gear stock (not sure if this is true in the OG Kalle edition), you achieve the same result 50/50 par distribution, just on a different manner.

What I struggle to understand is, once you have the car 50/50, front rear par distribution. What the itcc or central clutches are for (apart from disconnecting the rear end when using the handbrake)? If anyone can enlighten me on this topic, and how changing the itcc modes can affect driving when already 50/50 via hardware.

If you don’t use e.g. a Syvecs controller probably the only remaining function of the clutch is to disconnect the rear - as you wrote.

 

[ninjan00dles]

I have had 41201-52010 installed for some time now (no more overdriven rear). I honestly don’t feel a difference

 

[MRA3]

This video isn’t an answer to your question but nevertheless interesting!

Interesting. Big thing of the video for me is that they claim that rear diff and ITCC share the oil which is big news if that’s the case, because I think it was Fensport who first disassembled the ITCC pack and confirmed it was sealed for life.

 

[ninjan00dles]

Interesting. Big thing of the video for me is that they claim that rear diff and ITCC share the oil which is big news if that’s the case, because I think it was Fensport who first disassembled the ITCC pack and confirmed it was sealed for life.

They are indeed separate, that info is incorrect

 

[tonic]

I'm not entirely sure what problem this kit solves or if it's worth the compromise. Locking the torque split at 50:50 isn't some kind of miracle, it’s more like AWD technology from the early '80s. While useful on low-grip surfaces, it's terrible for tarmac. Since the front and rear wheels follow different paths in a turn, they should rotate at different speeds. Forcing them to turn at the same speed strains the drivetrain and reduces grip. That’s why manufacturers moved away from fixed 50:50 splits, some adopted Torsen center diffs and later - actively controlled ones.

JTEKT’s ITCC wasn’t developed specifically for the GR Yaris. Less performance oriented cars have used this system long before, but without an overdriven rear axle. Those systems simply adjusted torque bias between the front and rear from 100:0 to 50:50. I believe what Toyota presents as its newly developed AWD system, "GR-Four," is essentially the overdriven rear axle, which allows more torque to be sent to the rear when needed. This isn’t just Sport mode. GR-Four constantly adjusts torque distribution in other modes as well — for example, in Track mode, it shifts more torque to the rear under braking to help stabilize the car.

As for the overheating issue discussed in that YouTube video, it’s unlikely that the ITCC or rear differential is overheating. From information gatherred by 555 Engineering it seems that the AWD ECU applies a preemptive measure to protect the transfer case. While ITCC does have a temperature sensor it’s mainly there to maintain consistent torque distribution across a wide range of conditions, particularly in cold temperatures. A rear differential with a Torsen LSD generates more heat than an open diff but less than a clutch-based. I haven’t seen any data suggesting stock Torsen LSD suffers from temperature-related issues that need addressing.

 

[MRA3]

I'm not entirely sure what problem this kit solves or if it's worth the compromise. Locking the torque split at 50:50 isn't some kind of miracle, it’s more like AWD technology from the early '80s. While useful on low-grip surfaces, it's terrible for tarmac. Since the front and rear wheels follow different paths in a turn, they should rotate at different speeds. Forcing them to turn at the same speed strains the drivetrain and reduces grip. That’s why manufacturers moved away from fixed 50:50 splits, some adopted Torsen center diffs and later - actively controlled ones.

JTEKT’s ITCC wasn’t developed specifically for the GR Yaris. Less performance oriented cars have used this system long before, but without an overdriven rear axle. Those systems simply adjusted torque bias between the front and rear from 100:0 to 50:50. I believe what Toyota presents as its newly developed AWD system, "GR-Four," is essentially the overdriven rear axle, which allows more torque to be sent to the rear when needed. This isn’t just Sport mode. GR-Four constantly adjusts torque distribution in other modes as well — for example, in Track mode, it shifts more torque to the rear under braking to help stabilize the car.

As for the overheating issue discussed in that YouTube video, it’s unlikely that the ITCC or rear differential is overheating. From information gatherred by 555 Engineering it seems that the AWD ECU applies a preemptive measure to protect the transfer case. While ITCC does have a temperature sensor it’s mainly there to maintain consistent torque distribution across a wide range of conditions, particularly in cold temperatures. A rear differential with a Torsen LSD generates more heat than an open diff but less than a clutch-based. I haven’t seen any data suggesting stock Torsen LSD suffers from temperature-related issues that need addressing.

Is there a temperature sensor in the transfer case so the ECU can detect when it gets too hot? Os is just calculated based on other values and when they reach a certain temperature ecu cuts and stops 4WD system working

 

[Altocumulus]

Is there a temperature sensor in the transfer case so the ECU can detect when it gets too hot? Os is just calculated based on other values and when they reach a certain temperature ecu cuts and stops 4WD system working

It's calculated based on other inputs.

 

[Not.a.circuit.pack]

This is on a convenience pack car with no Torsen-like diffs?

This is the same on either model - Cusco RZ1.5-2Way on mine rather than Torsen

Toyota part 41201-52010 provides the same. It’s a 41/18-teeth transfer gear kit, matching the ratio of the rear differential.

If you like to go for something stronger, XSHIFT makes very strong 32/14-teeth transfer gear kit (https://www.xshiftgearboxes.com/hypoid-gearsets/toyota-gr-yaris).

Additionally it might be even matched with Kalle Rovanpera 39/17teeth rear diff kit (Toyota 41201-59435), giving GRY super strong equal ratio setup capable of fully locking 4WD (when matched with Syvec or other 4WD cotroller).

Wow, I didn't know about the alternative Toyota parts. Would be interesting to compare.
The X-shift hypoid kit isn't something I'd want to swap for, already running Kotouc up front and twin carbon ats clutch. Very happy with the setup as it's perfectly 50:50 now when locked, as opposed to being close to 50:50 with the x-shift.

The Brena kit is very nice and highest quality, but quite expensive...
Where did you get it from and was it easy to install? Probably you need various shims?

Got it from Christian at IRC. Didn't need any shims luckily, but they do sets they can supply.

If you don’t use e.g. a Syvecs controller probably the only remaining function of the clutch is to disconnect the rear - as you wrote.

Yes, but I don't have it locked all the time. Ryan at syvecs did some lovely mapping of the 4wd controller that give a lovely mix of capabilities.

I have had 41201-52010 installed for some time now (no more overdriven rear). I honestly don’t feel a difference

Really? I've found it almost night and day difference. Maybe some of it due to the mechanical differentials?

Interesting. Big thing of the video for me is that they claim that rear diff and ITCC share the oil which is big news if that’s the case, because I think it was Fensport who first disassembled the ITCC pack and confirmed it was sealed for life.

I'm sure they 'share' the same oil, in that it's the same grade, not that the two units are connected together?

I'm not entirely sure what problem this kit solves or if it's worth the compromise. Locking the torque split at 50:50 isn't some kind of miracle, it’s more like AWD technology from the early '80s. While useful on low-grip surfaces, it's terrible for tarmac. Since the front and rear wheels follow different paths in a turn, they should rotate at different speeds. Forcing them to turn at the same speed strains the drivetrain and reduces grip. That’s why manufacturers moved away from fixed 50:50 splits, some adopted Torsen center diffs and later - actively controlled ones.

JTEKT’s ITCC wasn’t developed specifically for the GR Yaris. Less performance oriented cars have used this system long before, but without an overdriven rear axle. Those systems simply adjusted torque bias between the front and rear from 100:0 to 50:50. I believe what Toyota presents as its newly developed AWD system, "GR-Four," is essentially the overdriven rear axle, which allows more torque to be sent to the rear when needed. This isn’t just Sport mode. GR-Four constantly adjusts torque distribution in other modes as well — for example, in Track mode, it shifts more torque to the rear under braking to help stabilize the car.

As for the overheating issue discussed in that YouTube video, it’s unlikely that the ITCC or rear differential is overheating. From information gatherred by 555 Engineering it seems that the AWD ECU applies a preemptive measure to protect the transfer case. While ITCC does have a temperature sensor it’s mainly there to maintain consistent torque distribution across a wide range of conditions, particularly in cold temperatures. A rear differential with a Torsen LSD generates more heat than an open diff but less than a clutch-based. I haven’t seen any data suggesting stock Torsen LSD suffers from temperature-related issues that need addressing.

Fully agree - but where this really shines is on full power launches and very hard cornering where all 4 wheels are spinning up. Makes it much more fun and predictable (arguably not as smooth as when the 4wd controller is trying to get everything all straight and true by adjusting the bias). I've only had heat issues with the A052s on and a hammering. The mechanical diffs are certainly what add to that.