Newbie9000

I just had a wet dream. Dreaming about being able to mix and mesh a Sc400 (1 UZ + a current now 2020 Toyota CVT) or swap the 4 speed for 8 speed
is it do able?

CLass of 1

That’s not a wet dream, that’s a nightmare.

CVT’s are not performance transmissions. End of discussion.

A RWD engine/transmission won’t work with a FWD transaxle transmission, either. This is dead on arrival.

Are you trying to achieve better fuel economy? Performance? If it’s the latter, you’re far better off equipping the car with a manual transmission (there are plenty of options) and learning to drive stick. If you want better fuel economy, I think a different car is in your future.

Nick

KahnBB6

iTrader: (5)

What CLass of 1 said ^^

A CVT is really, really not a good idea in an SC400 or SC300. Forget that you'd need an engine ECU capable of talking to the CVT so as to adjust the position of the internal bands. Those types of transmissions are not known to handle significant torque for many years without failure. Even more than that they are just about the worst feeling type of transmission that man has ever invented. Even if you *could* make it work would you really want your 1UZ to rev up to a fixed RPM while you accelerate so as to make it feel like you're driving a vacuum cleaner?

There are a couple of Lexus RWD "CVT" transmissions but these aren't what you're thinking of. They're more like self contained motor drive units with a start-stop assist motor and an additional acceleration motor. There has been success hacking and repurposing those as standalone EV conversion powertrains but not in bolting them to anything but the original GS450h or LS460h engines they were originally attached to.

If you have a 1998-2000 SC400 1UZ VVT-i then you've already got a potent and fuel efficient powertrain for the platform with a stock A650E 5-speed automatic transmission and factory 3.26:1 final drive ratio.

If you have a 1992-1997 SC400 then the improvement over the factory A340E 4-speed automatic would be a 5-speed manual conversion. You could lower the stock 3.92:1 final drive ratio to a 3.76:1, 3.615:1 or 3.26:1 but with the very last ratio you'll have a dog of a drivetrain that won't accelerate well against a 250-260hp 1UZ-FE V8.

If you really want a far more fuel efficient drivetrain than was offered in a USA-spec SC then you could seek out a complete 2JZ-FSE engine set with its factory transmission, engine harness and ECU attached and go to the trouble of swapping it into your SC400 (it will fit right in since it is a JZ engine and the car was designed for it). That engine has a narrow valve angle cylinder head with Toyota's D4S direct injection system and dual VVT-i on the intake and exhaust camshafts. It makes 217hp. There is ZERO high performance modification potential with it but technically it has greater fuel efficiency than any USA-spec 2JZ engine or a 1UZ-FE engine.

But it would be SO much work for that single goal only. And several parts for servicing it are JDM-only meaning you'd need to buy them from Amayama probably.

....

Now you can swap over any kind of transmission that you have an adapter kit ready to help you bolt it on with. A modern 8-speed automatic from, say, a Lexus RC-F could *probably* be made to bolt up with enough work to develop the parts needed to make it fit. But then you would need a way to control the transmission since automatics receive their control signals from the main engine ECU an your SC400's factory ECU is designed to send signals to its original four speed automatic.

An aftermarket standalone engine ECU would be needed not only to control whatever swapped over automatic you'd use but also to do a full map and tune of the engine itself.

This is why converting an automatic car to use a manual transmission... ANY manual transmission... is far easier than converting an older car (auto or manual) to use a modern automatic transmission.
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You could try getting a complete 1UZ-FE VVT-i and its engine-specific version of the A650E 5-speed automatic transmission from a 1998-2000 SC400 or the same from a 1998-2000 LS400 or 1998-2000 GS400 and then swap that over to your earlier SC400, plus the required 3.26:1 rear diff (from an SC400 98-00 or a few other Lexus models). That in itself is a ton of work to convert the wiring harness to work with your SC chassis. You'd then have a stock 290hp, 300ft-lbs of torque and around 26mpg on the highway.

But again... that swap is almost never done as it is a tremendous amount of work when you could just keep an eye out for a 1998-2000 SC400.

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Please though... please... don't try to bolt any type of rear-drive based CVT transmission to your 1UZ-FE V8. Those types of transmissions really are terrible to use and unreliable footnotes in automobile transmission history.