Next-Generation Lexus IS Sedan to get Twin-Turbo V6 F SPORT?

Posted by Kevin on July 4th, 2018

The Australian website Driving Enthusiast is claiming the next-generation Lexus IS sedan will be available with the 3.5L twin-turbo V6 engine from the LS flagship:

The rumoured 2020 Lexus IS 400 isn’t set to be a full-cream performance model by F division, but more of a sub-performance version by its F Sport sector. It’s believed it will feature a range of performance-inspired features, such as large wheels hiding big brakes, sports suspension, and the usual F Sport treatment for the interior.

As for that engine. Lexus introduced its first turbocharged petrol engine, codenamed ‘V35A-FTS’, with the LS 500. The 3.5-litre twin-turbo unit essentially comes in to replace the naturally aspirated 3.5-litre V6.

Let’s just be upfront — this news is coming from an unsubstantiated source, there’s nothing to back up these facts. However, the V35A-FTS twin-turbo V6 makes perfect sense in the next-generation IS sedan.

That said, 416 horsepower seems excessive in the standard model, and Lexus has yet offer serious performance upgrades with their F SPORT models. If the rumor is correct and the TTV6 is not meant for the next-generation IS F, then what powers that car?

(We could stack rumors on top of each other, and suggest a detuned version of the much-hyped twin-turbo 600-horsepower V8 for the IS F. Also, the image above was a rendering of the next-gen GS F and unrelated to the IS at all.)

Lexus IS: Third Generation
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Comments
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
L
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.
S
Levi
GS4 has a 5cm longer wheelbase than IS3, yet is almost 20cm longer overall. It means the remaining 15cm happen at the overhangs. Overhangs are what make a car huge and difficult to drive in tight spaces, because it is harder to estimate the overhangs, that to feel the wheelbase. If the new IS gets a slightly longer wheelbase, where all to added space goes to rear seats, but overhangs remain short, it would remain a 'compact' sporty sedan, with rear seats good for long trips.
This is why the LWB 3-series gets much more rear space than SWB 5-series despite being much shorter; in fact the sub-4.8m 3-Series L has more legroom than full-size SUVs like the GLS or Range Rover. It's ridiculously space efficient.
However, for the IS a lot of wheelbase stretch will be used to allow a FMR layout (if they keep doing it for the IS). I'm expecting at most 50mm/2in longer interior cabin to make the rear usable but definitley not spacious. But usable is all they need.
To me a 4GS with 50mm shorter overhangs and front axle moving forward by 20mm is a perfect size for 4IS. The side profile of the 4GS looks very compact for its actual size. I don't think maneuvrability is a concern for sedan shoppers since they are already sacrificing maneuvrability by choosing a sedan in the first place. The only place where a 4800mm IS could have major difficulty moving is Japan, but the compact-size 3IS is a whale on Japanese roads already.

S