Building an IS350 6MT
11-23-15, 11:02 PM
#1
Building an IS350 6MT
After years of waiting and researching, I feel like everything is right for me to start this project and I'm pretty excited to say the least!
While there has been a lot of talk over the years about whether the 6MT in the IS250 can handle the stresses of the IS350 engine, among other issues. I feel that the RA62 gets kind of a semi-undeserved bad rap. I feel it wasn't necessarily the best transmission to use in the Lexus, I don't find it to be particularly horrible though I have definitely driven better. Still, I feel it is more than up to the task of sitting behind the 2GR-FSE.
So where does this leave me? With a few parts sitting beside my 2011 IS250 6MT and waiting to be installed:
Similar to the way you can transform between current and voltage in electronics, when working with gearing you can exchange speed for torque. High current flow requires thicker wires, but if you want to transmit power using smaller wires, you can do it using higher voltage. That is similar to the principle used in the RA6x series gearboxes like the one used in the IS250 (keeping the RPM higher to reduce the torque applied to the gears). It has often been talked about that the shafts aren't supported well enough or that the tapered roller bearings aren't strong enough in the RA62 to support the torque generated by the IS350. Instead of an input reduction gear, an output reduction gear is used. What this means is that instead of the torque being increased before the gears on the input shaft, it is done after the gears on the output shaft. This is one of the reasons why the input shaft requires less support (no center support bearing). It also means the gears don't need to be as large and can handle loads greater than gears of the same size would in an input reduction manual transmission. Overal, it is designed to be smaller and lighter than other gearboxes that can support similar torque loads. It is not an all-out strong design like a Getrag 233/Toyota V160 or even the R154, but it was never designed to be.
The RA62 is an Aisin AY6 transmission, and it has been used in many cars (both Toyota/Lexus and other brands). In Toyota and Lexus models it used in vehicles like the Tacoma (RA60), FJ Cruiser (RA61), IS250 (RA62) and IS220d (RA63). In other brands it was used in cars like the Chevrolet Camaro, Cadillac CTS and Holden Commodore. The two best examples of what the transmission is capable of handling are the FJ Cruiser and IS220d. The FJ Cruiser has 278 ft-lbf of torque in a 4,400lbs vehicle and the IS220d has 300 ft-lbf of torque in the actual 2IS body. The transmission is rated by Aisin to support 345 ft-lbf. The gears can take what the 2GR-FSE can throw at it.
So if we know that the transmission can handle the 2GR-FSE, what can't? The clutch. The stock clutch used with the 4GR-FSE is only rated for 250 ft-lbf. Well below what the 2GR-FSE puts out (277 ft-lbf). Thankfully this can be increased relatively easily with a heavier pressure plate in the 15% or so heavier range.
Next is the rest of the driveline, looking at the gearing that Lexus used for the 2GR and 4GR, you'll find that (expectedly) the torque output curve of both engines is quite similar and in fact the gearing between the engines is so similar that the RA62 with it's 3.73:1 final drive gearing in the IS250 6MT is actually almost identical to the A760 with it's 4.08:1 final drive gearing in the IS350 RWD. Nice. The differential used in the IS250 has been used by Toyota in vehicles with even more torque than the 2GR is capable of putting out, and in modified vehicles much more than that.
Jeff
While there has been a lot of talk over the years about whether the 6MT in the IS250 can handle the stresses of the IS350 engine, among other issues. I feel that the RA62 gets kind of a semi-undeserved bad rap. I feel it wasn't necessarily the best transmission to use in the Lexus, I don't find it to be particularly horrible though I have definitely driven better. Still, I feel it is more than up to the task of sitting behind the 2GR-FSE.
So where does this leave me? With a few parts sitting beside my 2011 IS250 6MT and waiting to be installed:
Similar to the way you can transform between current and voltage in electronics, when working with gearing you can exchange speed for torque. High current flow requires thicker wires, but if you want to transmit power using smaller wires, you can do it using higher voltage. That is similar to the principle used in the RA6x series gearboxes like the one used in the IS250 (keeping the RPM higher to reduce the torque applied to the gears). It has often been talked about that the shafts aren't supported well enough or that the tapered roller bearings aren't strong enough in the RA62 to support the torque generated by the IS350. Instead of an input reduction gear, an output reduction gear is used. What this means is that instead of the torque being increased before the gears on the input shaft, it is done after the gears on the output shaft. This is one of the reasons why the input shaft requires less support (no center support bearing). It also means the gears don't need to be as large and can handle loads greater than gears of the same size would in an input reduction manual transmission. Overal, it is designed to be smaller and lighter than other gearboxes that can support similar torque loads. It is not an all-out strong design like a Getrag 233/Toyota V160 or even the R154, but it was never designed to be.
The RA62 is an Aisin AY6 transmission, and it has been used in many cars (both Toyota/Lexus and other brands). In Toyota and Lexus models it used in vehicles like the Tacoma (RA60), FJ Cruiser (RA61), IS250 (RA62) and IS220d (RA63). In other brands it was used in cars like the Chevrolet Camaro, Cadillac CTS and Holden Commodore. The two best examples of what the transmission is capable of handling are the FJ Cruiser and IS220d. The FJ Cruiser has 278 ft-lbf of torque in a 4,400lbs vehicle and the IS220d has 300 ft-lbf of torque in the actual 2IS body. The transmission is rated by Aisin to support 345 ft-lbf. The gears can take what the 2GR-FSE can throw at it.
So if we know that the transmission can handle the 2GR-FSE, what can't? The clutch. The stock clutch used with the 4GR-FSE is only rated for 250 ft-lbf. Well below what the 2GR-FSE puts out (277 ft-lbf). Thankfully this can be increased relatively easily with a heavier pressure plate in the 15% or so heavier range.
Next is the rest of the driveline, looking at the gearing that Lexus used for the 2GR and 4GR, you'll find that (expectedly) the torque output curve of both engines is quite similar and in fact the gearing between the engines is so similar that the RA62 with it's 3.73:1 final drive gearing in the IS250 6MT is actually almost identical to the A760 with it's 4.08:1 final drive gearing in the IS350 RWD. Nice. The differential used in the IS250 has been used by Toyota in vehicles with even more torque than the 2GR is capable of putting out, and in modified vehicles much more than that.
Jeff
Last edited by Jeff Lange; 12-13-19 at 10:02 AM.
The following 3 users liked this post by Jeff Lange:
11-24-15, 10:41 AM
#5
Enjoy the swap, Jeff. You've always been very knowledgeable in the parts department.
I'm sure you've ran across the guy in Australia i believe who swapped a 350 engine into his 250 manual? Not sure if he's active to PM any questions but its worth mentioning in case you didnt know about it or others wanted to see.
http://au.lexusownersclub.com/forums...version/page-2
I'm sure you've ran across the guy in Australia i believe who swapped a 350 engine into his 250 manual? Not sure if he's active to PM any questions but its worth mentioning in case you didnt know about it or others wanted to see.
http://au.lexusownersclub.com/forums...version/page-2
11-24-15, 11:02 AM
#6
I did speak with that guy in Australia, yeah, though he didn't provide me with any more information than I already had to be honest. They also decided to go with the Fidanza flywheel, but I've decided to keep the dual-mass flywheel with a rubber-dampened clutch disc. I feel it will help dampen the driveline more than just using a sprung disc, and I've never been a big fan of aluminum flywheels. Perhaps if someone made a different flywheel I would consider it, but alas, the RA62 does not have much aftermarket support unfortunately.
I hope to have (what I assume to be) the first LHD IS350 6MT.
Jeff
I hope to have (what I assume to be) the first LHD IS350 6MT.
Jeff
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11-24-15, 11:56 AM
#8
Thank you so much Jeff for attempting this!Its my dream to swap the 350 engine to my 250 manual!You really gave me hope when you said that it can be done even without having VDIM.Please confirm that while you proceed with your swap.You only bought the 350 engine,not the 350 trunny?Our trunny is a direct fit to the 350 engine?Sorry for all these questions but I m so excited!I wish you the best of luck!I m looking forward to seeing your progress!
11-24-15, 12:43 PM
#10
Mechanically the transmissions are interchangeable, yes, however they are not controlled in the exact same way in some cases (especially between AWD/RWD), and so the IS350 computer may not control an IS250 transmission correctly. That said, I have a manual transmission and so I have a completely different can of worms to deal with. I also have not researched the differences in transmission control systems at all between the IS250 and IS350 or RWD and AWD. The IS250 AWD has a very similar transmission to the IS350 AWD, much more so than the IS250 RWD to IS350 RWD. If you had an IS250 AWD and did the IS350 AWD engine and harness, I would expect it would likely be an easier swap than RWD, but still not just plug and play.
Jeff
Jeff
The following 2 users liked this post by WylieKylie:
Jeff Lange (05-17-18),
SevenInked (03-27-24)
11-25-15, 11:01 AM
#15
I've got most of the rest of the parts I need now for the swap, though I am still waiting for a couple. I will be changing all the engine gaskets and seals before moving forward and I have the new connectors to modify the harness for the 6MT as well. Jeff