Swapping out 3.76 Torsen for 4.08. Will I hate it with single turbo?
10-13-15, 04:05 AM
#1
Swapping out 3.76 Torsen for 4.08. Will I hate it with single turbo?
Hi,
My 3.76 Torsen is bad. We are swapping it for a 4.08 from a Soarer. What differences might I experience aside from more shifting? Does it sound like a bad move? I drive mostly stoplight to stoplight in NYC and 45minute highway commute to work a few days per week. I rarely hold 70/80 mph more than a few minutes. Is there anything I may like better with the 4.08?
Thanks
Sc300 NA/T 450-500hp R154
My 3.76 Torsen is bad. We are swapping it for a 4.08 from a Soarer. What differences might I experience aside from more shifting? Does it sound like a bad move? I drive mostly stoplight to stoplight in NYC and 45minute highway commute to work a few days per week. I rarely hold 70/80 mph more than a few minutes. Is there anything I may like better with the 4.08?
Thanks
Sc300 NA/T 450-500hp R154
10-14-15, 02:55 AM
#4
Well even the '96+ Soarer 1JZ VVT-i 5-speeds came with a 4.08 diff and in stock tune they build a tremendous amount of their maximum torque from only 2400rpm. Of course that's only "280" horsepower versus your 500.
Estomax is the perfect guy to comment on this, however, since he has that engine
^^ Yes, low end acceleration will improve and you'll have a greater chance for wheelspin once your boost kicks in. 4.08 should do fine for a stopgap solution until you can get your TT Auto diff rebuilt. Though if there is no LSD you may want to turn down the boost a bit for now.
... now on the other hand, if you really do have a Soarer 4.08 diff with an LSD and not just an SC300 5-speed 4.08 open diff, you may actually have the newer Torsen T-2 in that thing. Technically better than the T-1 in your TT Auto. I assume this is probably not the case and it's just an open 4.08 but if I were in your shoes and if it's a T-2 Torsen in there it certainly would complicate my sound decision making skills
Alternatively you could swap in a common 3.92 diff from an SC400.
Estomax is the perfect guy to comment on this, however, since he has that engine
^^ Yes, low end acceleration will improve and you'll have a greater chance for wheelspin once your boost kicks in. 4.08 should do fine for a stopgap solution until you can get your TT Auto diff rebuilt. Though if there is no LSD you may want to turn down the boost a bit for now.
... now on the other hand, if you really do have a Soarer 4.08 diff with an LSD and not just an SC300 5-speed 4.08 open diff, you may actually have the newer Torsen T-2 in that thing. Technically better than the T-1 in your TT Auto. I assume this is probably not the case and it's just an open 4.08 but if I were in your shoes and if it's a T-2 Torsen in there it certainly would complicate my sound decision making skills
Alternatively you could swap in a common 3.92 diff from an SC400.
10-14-15, 05:09 AM
#5
Well even the '96+ Soarer 1JZ VVT-i 5-speeds came with a 4.08 diff and in stock tune they build a tremendous amount of their maximum torque from only 2400rpm. Of course that's only "280" horsepower versus your 500.
Estomax is the perfect guy to comment on this, however, since he has that engine
^^ Yes, low end acceleration will improve and you'll have a greater chance for wheelspin once your boost kicks in. 4.08 should do fine for a stopgap solution until you can get your TT Auto diff rebuilt. Though if there is no LSD you may want to turn down the boost a bit for now.
... now on the other hand, if you really do have a Soarer 4.08 diff with an LSD and not just an SC300 5-speed 4.08 open diff, you may actually have the newer Torsen T-2 in that thing. Technically better than the T-1 in your TT Auto. I assume this is probably not the case and it's just an open 4.08 but if I were in your shoes and if it's a T-2 Torsen in there it certainly would complicate my sound decision making skills
Alternatively you could swap in a common 3.92 diff from an SC400.
Estomax is the perfect guy to comment on this, however, since he has that engine
^^ Yes, low end acceleration will improve and you'll have a greater chance for wheelspin once your boost kicks in. 4.08 should do fine for a stopgap solution until you can get your TT Auto diff rebuilt. Though if there is no LSD you may want to turn down the boost a bit for now.
... now on the other hand, if you really do have a Soarer 4.08 diff with an LSD and not just an SC300 5-speed 4.08 open diff, you may actually have the newer Torsen T-2 in that thing. Technically better than the T-1 in your TT Auto. I assume this is probably not the case and it's just an open 4.08 but if I were in your shoes and if it's a T-2 Torsen in there it certainly would complicate my sound decision making skills
Alternatively you could swap in a common 3.92 diff from an SC400.
I was told it was a Soarer 4.08 LSD with known low mileage. I LOVED DRIVING with it yesterday. I was hovering so close to boost RPM's it was a blast. I actually use 5th regularly with the 4.08 and stay in boost more. I'll put the 3.76 back in for MPG and tranny heat but boy is it fun.....
Thanks Kahn!!!!
10-14-15, 04:23 PM
#7
Sure thing Studio! Now you've got me thinking about finding a Soarer 4.08 LSD diff myself and not rebuilding my diff with the 3.76 gears Probably not a good idea since I already take 1st and 2nd gears to reach 60mph and would probably hate that with turbos even at only 350whp
Love aggressive gearing myself but I am looking forward to less highway revs with only five speeds. Though it makes me wonder what R32/R33 GT-R's have as highway cruise rpms since they have at least 4.10 or 4.30 rear final drives.
Love aggressive gearing myself but I am looking forward to less highway revs with only five speeds. Though it makes me wonder what R32/R33 GT-R's have as highway cruise rpms since they have at least 4.10 or 4.30 rear final drives.
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10-14-15, 05:13 PM
#8
Sure thing Studio! Now you've got me thinking about finding a Soarer 4.08 LSD diff myself and not rebuilding my diff with the 3.76 gears Probably not a good idea since I already take 1st and 2nd gears to reach 60mph and would probably hate that with turbos even at only 350whp
Love aggressive gearing myself but I am looking forward to less highway revs with only five speeds. Though it makes me wonder what R32/R33 GT-R's have as highway cruise rpms since they have at least 4.10 or 4.30 rear final drives.
Love aggressive gearing myself but I am looking forward to less highway revs with only five speeds. Though it makes me wonder what R32/R33 GT-R's have as highway cruise rpms since they have at least 4.10 or 4.30 rear final drives.
Of all the ratios available, Lexus chose the 4.08 for an NA Sc300. It would have to be wonderful with an LSD version.
The 4.08 is ideal for my usual environment. On the long drives, I would eventually prefer the 3.76. I have the 400 for 8 hr. drives luckily.
10-14-15, 06:05 PM
#9
A problem they could have solved by offering the 1JZ-GTE here
I really think they kept the 4.08 for two reasons: it was the same part R&D'd for the Soarer 5-speed (simplicity on the assembly line) and also because it doesn't feel as aggressive as the 4.27 which might have been considered un-Lexus like. Yeah, we should have had a factory LSD option just like the MKIV NA.
I tend to agree with you: I love the short gearing (NA) for most of my driving and for highway acceleration. But on long drives I have become used to keeping my cruising at 80mph or below for max fuel efficiency. Fuel economy was always just a bit better with the 4.08 but I feel the tradeoff in power-band response makes the 4.27 a no brainer tradeoff for an NA. At 70mph there is only a 200-300rpm difference between the two. Much bigger difference at 70mph between 4.08 and 3.76.
With 500hp of boost though, especially with the 3.0L I think 3.92 and 3.76 are best. The 4.08 makes more permanent sense with the higher revving 2.5L turbo.
I really think they kept the 4.08 for two reasons: it was the same part R&D'd for the Soarer 5-speed (simplicity on the assembly line) and also because it doesn't feel as aggressive as the 4.27 which might have been considered un-Lexus like. Yeah, we should have had a factory LSD option just like the MKIV NA.
I tend to agree with you: I love the short gearing (NA) for most of my driving and for highway acceleration. But on long drives I have become used to keeping my cruising at 80mph or below for max fuel efficiency. Fuel economy was always just a bit better with the 4.08 but I feel the tradeoff in power-band response makes the 4.27 a no brainer tradeoff for an NA. At 70mph there is only a 200-300rpm difference between the two. Much bigger difference at 70mph between 4.08 and 3.76.
With 500hp of boost though, especially with the 3.0L I think 3.92 and 3.76 are best. The 4.08 makes more permanent sense with the higher revving 2.5L turbo.
Last edited by KahnBB6; 07-23-18 at 03:09 AM. Reason: Grammatical corrections and cleanup
