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Read the PDF. Volts and amps are power. Resistance only plays if you calculate power using current squared times resistance. Power is defined as I*E. If power is constant when one goes up the other goes down. Same with gearing. Power doesn't change, and your trap speed attests to this. If we had a three or four speed gearbox, yes, lower final drive would make a much bigger difference.
"If you want force, you lose rotation. If you want rotation you lose force. Very similar to volts and amps in electricity."
In this statement, force goes up rotation goes down, which you compare in volts and current to electricity. In electricity, Ohm's law states that Volts and Current is proportional, meaning if volts go up, current will also go up.
But yes, I agree, if we didn't have an 8 speed gearbox, the final drive change would be effective.
Yeah I’m on jackstands, trying to pry the driver side and passenger side popped back in so I concentrated on one side only. I just broke everything loose on both sides but didn’t remove anything besides the bolt for the control arm to the hub (near the rear strut). I made a mistake and did not remove the plates under the axles covered by the plastic cover. As soon as I removed those plates, I was able to drop the diff lower (wow big shocker) lol so I dropped it as low as I could, popped the driver side out, jacked the diff back up and mounted it quickly, got the passenger to pop out, dismounted, lowered diff, and removed the passenger side with ease. Had I known or thought to remove those plates, this would have been done as I was able to drop the diff a lot lower. Prepping for install
/slightly O/T but the 350 will have an OSG TCD here shortly and like you, it will be on jack stands for 3rd member R&R.
Can you elaborate about "plates under the axles" that aided in dropping diff without suspension tear down? Are you talking about the diagonal stamped brace shown here?
Worst case I unbolt shock bottom, sway bar link, LCA pivot and strut bar, but if it can be snaked out without that and stabbing axles can be done without wrecking seals, I'll try it.
Thanks in advance!
/slightly O/T but the 350 will have an OSG TCD here shortly and like you, it will be on jack stands for 3rd member R&R.
Can you elaborate about "plates under the axles" that aided in dropping diff without suspension tear down? Are you talking about the diagonal stamped brace shown here?
Worst case I unbolt shock bottom, sway bar link, LCA pivot and strut bar, but if it can be snaked out without that and stabbing axles can be done without wrecking seals, I'll try it.
Thanks in advance!
Yeah brother those are the ones (each side). Sorry for the late response, im currently deployed and finally had enough bandwidth to load my gmail and saw this in my inbox. I surprisingly have enough bandwidth to load CL and reply lol. Before i left, i went back to the stock diff and did a few 1/4 miles (with r888rs). I could not get my times to what i had with the gs diff and r888rs. The difference is gs diff w/ r888rs 12.48 and stock diff 12.51 w/ r888rs. Mind you, DA was higher (1700+ in NC summer) when i had the gs diff. I have an xforce exhaust, vivid racing tune, and afe drop in dry filter.
Just wanted to share some results going from 2011 Torsen lsd to a 2007 GS450 open diff on my 2011 Lexus ISF. Fyi I love drag racing my car. My two local tracks are Sacramento and Sonoma Raceway.
October 28th at Sacramento. Dont mind the inaccurate timeslip receipt date. OEM LSD and 245/45/17 MT Street R tires.
November 8 at Sacramento. GS450 open diff with 245/45/17 MT Street R tires.
In a separate run yesterday, I trapped 120.56mph. So far the GS450 diff is helping my 60fts and times. I plan on racing a few more times this year. Goal is to hit 11.73 or faster.
Just wanted to share some results going from 2011 Torsen lsd to a 2007 GS450 open diff on my 2011 Lexus ISF. Fyi I love drag racing my car. My two local tracks are Sacramento and Sonoma Raceway.
October 28th at Sacramento. Dont mind the inaccurate timeslip receipt date. OEM LSD and 245/45/17 MT Street R tires.
November 8 at Sacramento. GS450 open diff with 245/45/17 MT Street R tires.
In a separate run yesterday, I trapped 120.56mph. So far the GS450 diff is helping my 60fts and times. I plan on racing a few more times this year. Goal is to hit 11.73 or faster.
Originally Posted by Jwconeil
Why not swap the torsen LSD unit into the gear set you want to run long term?
@Positron i was going to say.. I did a lot of work to get a RC F Torsen LSD into my 08' IS F..
Is the GS450 diff the same as an open diff found on the IS350 ?? If that gear set is better for your 1/4 miles times just drop in an OS Giken unit so you can plant the power down equally..!!
Edit - I just did all the backwards reading... Can't say I would want to swap into these gear ratio issues for daily driving..
@Positron i was going to say.. I did a lot of work to get a RC F Torsen LSD into my 08' IS F..
Is the GS450 diff the same as an open diff found on the IS350 ?? If that gear set is better for your 1/4 miles times just drop in an OS Giken unit so you can plant the power down equally..!!
The IS350 has a 4.08 gear ratio. Two of my friends have had them in their cars. One of them hit 11.75 at the track. Which is the time I am trying to beat . Both have said it's too aggressive around town and etc. That's why I settled for the 3.7 diff. I'll try to do the OS giken unit next year.
Overall I really like the driving style of the 3.7 diff. From driving around town, freeway pulls and 1/4 mile racing.
The IS350 has a 4.08 gear ratio. Two of my friends have had them in their cars. One of them hit 11.75 at the track. Which is the time I am trying to beat . Both have said it's too aggressive around town and etc. That's why I settled for the 3.7 diff. I'll try to do the OS giken unit next year.
Overall I really like the driving style of the 3.7 diff. From driving around town, freeway pulls and 1/4 mile racing.
These are the part numbers for various gear ratios that will potentially fit the IS F rear end. I take no responsibility for them actually working, so good luck, haha. Some of the associated hardware/seals that are included in the set may need to be swapped out, but the ring and pinion sets should fit the IS F diff.
2.474:1 - 41201-59165
2.764:1 - 41201-59305 or 41201-59345
2.937:1 - 41201-59235 or 41201-59275
3.133:1 - 41201-59245 or 41201-59285
3.266:1 - 41201-19645 or 41201-80445
3.357:1 - 41201-59215 or 41201-59335
3.461:1 - 41201-49155
3.615:1 - 41201-59055 or 41201-59355
3.769:1 - 41201-59065
3.917:1 - 41201-59035 or 41201-80029
4.083:1 - 41201-59175 or 41201-59315
4.273:1 - 41201-80028
Hey all, I come from the Honda scene and typically there is that one FD ratio that is perfect increased performance while still within daily driving liveability.
After reading through this thread, its unclear that there is a 'go-to' upgrade option for the ISF? The general consensus is OEM FD ratio is as optimal as it gets for daily and performance? Anything higher will provide marginal gains and noticeable affect daily driveability?
I heavily considered changing my gear ratio, but ultimately the gains are marginal at best. This doesn’t seem to be a very effective mod since we have an 8 speed trans that keeps the car in the desired power band. I’d imagine it feels peppier, so it may be funner to drive. We just aren’t seeing drastic changes with gear ratio adjustments so far.
Has anyone else seen anything to the contrary? I’m a few 10ths away from 11s, but can’t seem to find them anywhere.
After reading through this thread, its unclear that there is a 'go-to' upgrade option for the ISF? The general consensus is OEM FD ratio is as optimal as it gets for daily and performance? Anything higher will provide marginal gains and noticeable affect daily driveability?
The 3.13 gear ratio may be the 'go-to' upgrade option for the IS-F. It is the ratio that all RC-Fs changed to in 2020 and is used on the Track Editions to get that under 4 sec. 0-60 time.
Hey all, I come from the Honda scene and typically there is that one FD ratio that is perfect increased performance while still within daily driving liveability.
After reading through this thread, its unclear that there is a 'go-to' upgrade option for the ISF? The general consensus is OEM FD ratio is as optimal as it gets for daily and performance? Anything higher will provide marginal gains and noticeable affect daily driveability?
Probably 3.13 to 3.3 are the best middle ground. The 2018+ IS f-sports all come with 3.13 LSD now, so thats what I'm looking for.
Sorry to bump this but this was very interesting to read. Thank you for this.
On the 3IS350 we have kind of the opposite issue- we have the same 8-speed as you guys but the 3.13 diff and the result is that it's _slower_ to 60mph than the 2IS350 with the 4.08. On our measly V6s we could use a little more "hot rod" on the normal roads. There's not a lot of documentation on people doing that swap yet. I have the added bonus of having an LSD, so if I want to keep that and have 4.08, it obviously won't just be a pumpkin swap.
. Both have said it's too aggressive around town and etc. That's why I settled for the 3.7 diff. I'll try to do the OS giken unit next year.
