ISFpowered

Trying to make a choice here. I知 in NorCal if anyone has a 3.7 I知 open to roll racing in a controlled environment AKA Mexico. I知 curious to know which has the advantage over the other if any at all. Dig racing obviously 3.7 takes it but what about roll racing from 20-150 or even 40-160?

Jwconeil

I only think Dig racing has like maybe a hair second jump 0-60. Most of the data we have seen shows that the 2.9 is a great ratio for this car. I too went down this road, but all the posted times had such minor differences that they could be accounted for simply by a slight change in weather. It痴 a pretty high cost to find another diff and then throw an LSD in it, so I decided it wasn稚 worth it. I壇 love to be proven wrong, simply because I知 about 3/10s off my goal of running elevens. If a diff could get me there, I壇 do it. After a dig, I don稚 think there is going to be much, if any, difference because our cars are always in their power and with so many gears.

ISFpowered

A friend of mine has a 3.7 diff and he runs 11.65. He posted it on YT but I wonder how we would do roll racing especially since we have the setup aside from the diff. My best time has been a 12.0 so the difference in quarter mile time is pretty significant but I wonder how we would do roll racing. Tough call but if he edges me out I知 swapping over to the 3.7 diff immediately.

Jwconeil

Was this him?

https://www.clublexus.com/forums/is-...-record-2.html

He looks pretty gutted when he ran that time, including no sunroof glass. I壇 be interested in his times with the 2.90, but if your trying to gauge what difference the differential may have made alone, see the link below.

See here - pg 14-15.

https://www.clublexus.com/forums/is-...or-not-15.html

This may be a better gauge of what a diff swap will do. He gained less than 1/10 in the quarter. This is a bit more objective. Ignore the title, the poster on page 15 had a 3.7 diff, not a 3.2.

Also see post 842 in this thread. He dropped 5/100s in the sixty by getting the same diff.

https://www.clublexus.com/forums/is-f-2008-2014/410966-official-is-f-drag-time-dyno-time-performance-thread-57.html

ISFpowered

Yes, it痴 Positron. I would definitely like to see how a roll race plays out though. Very interested in this.

lobuxracer

iTrader: (2)

If the cars weigh the same, have the same drivetrain except the final ratio, and both start with the engine near peak power, the final drive ratio won't make any difference at all. Gearing is mathematics, and if the engines are both producing the same power at the same time, the gearing won't make a difference. The exact same amount of power is being sent to the wheels so the acceleration will be the same. With 8 gears available, this is even more likely to be true because the difference in power between the two configurations will be near zero.

Joe Z

iTrader: (10)

For reference the newer 2021 IS's with Torsen LSD units are now coming with 3.133 Final-drive gearing..
(same for inbound 2022 IS 500)

Also back in 2020 they did the same on ALL the RC F's

Joe Z

Justind27

iTrader: (6)

I ran the is350 diff (mind you os giken super lock modded) which made it a 4.10 ratio, it topped out at 124mph in 3rd with 275/35r19 rear tires. The acceleration was stupid fun, top speed was only 125 mph, power transfer would be great if I used slicks and it likely would have seen close 11 seconds, it痴 all documented with track slip info back when. I壇 say go 4.10 but have the gov deleted with a tune and rock it for a little while, it was easy enough to swap the whole pumpkin

Jwconeil

TAS02 ran the IS350 gear and had the same ET. I know it seems counter intuitive, but nobody has swapped gears and actually went substantially faster. This is notable, because a few of our members have swapped Gears. First gear accelerated hard at the cost of traction. The gears pass very quickly, and you have to shift 2 extra times in a quarter. You then top out at 130, and there were reported drivability issues with the 4.09 gear. The ECU didn稚 seem to like it.

The gains have always been .05 or maybe even .1, but that isn稚 really proof of anything. My car will vary by a half second depending on track prep and weather (granted I live in Indiana, and our weather swings hard).

I threw a 4.10 in an old trans am and it made a wild difference, but our 8 speed ISF trans really negates most of recordable value, and your stuck with all the cons.

It will make the car much more violent and raw... so it値l feel much faster.

Im with OP... I壇 LOVE it to make a difference. I even started lining up part numbers to buy a diff and throw a Giken in it. IN A Drag scenario, it won稚 really help. In a road course scenario, it would hurt a lot based on how much shifting would be required.

Did Lexus ever publish why they went to a 3.1 gear? I知 sure there is value there, otherwise Lexus wouldn稚 have bothered.

ISFpowered - if you swap, keep us updated. I致e grown to appreciate your input on this chassis. I just wanted to share some of the research I did. It scared me off from the project.

McPierson

iTrader: (3)

In a drag: Traction... if you致e got wheel spin with the 2.9 it will be basically the same with lower gears.

if you have no spin then lowering gears will get you closer to the traction limit on the tires at lower rpm and you will go faster sooner out of the hole.

In roll racing you値l already be in the meat of the powerband and then it痴 just math like lobux and others have said.

there are probably reasons to regrear on the track if a particular turn is between gears. That痴 not likely worth it on an 8 speed. But I知 just a bench racer.