And how much slower is it actually, if you were to race the two side by side.

 

Why? Probably for Lexus to make a higher profit margin or mark off some money for people who don't care, probably going to have to go to Japan and find that out.

260hp & 236lb/tq vs 311 & 280lb/tq

is300 0-60mph 6.3-6.7 seconds
is350 0-60mph ~5.6 second

So about a second faster and the difference would increase as time goes on

 

From what I remember driving my 2016 IS 300 AWD, the seat-of-the-pants feel was not very different between a 350 and it. RWD and AWD will obviously be different because of the transmissions.

Motor Trend tested a 2021 IS 300 AWD and managed a 5.7-second run to 60, for whatever that's worth.

https://www.motortrend.com/reviews/2...wd-first-test/

edit: I'll also say this. Last night I went for a drive, and I noticed that, for whatever reason the 350 really wakes up above 4500 RPM, specifically in third gear. I do not remember feeling that in my 300 AWD. Futhermore, since the gearing is a little shorter in the RWD car, you are more likely to experience this without losing your license in a 350. The 300 AWD is not a slow car by any means, and a good driver would be able to keep up with a 350 no problem.

 

^^ I agree with what you stated 200%!

 

I think the reason it’s de tuned is to make the AWD more reliable with less horsepower and torque going through the system. The cost for de tuning would be zero as its an ecu tweak.

 

I don't think reliability was even a thought with the creation of the 300 AWD. When introducing the IS 300 AWD for the first time, the sole reason they did the detuning is to maintain the hierarchy of 350 > 300 without re-working the then-new 8AR-FTS engine to fit with the AWD transfer case/6-speed automatic transmission. With the IS 250 AWD, you had the same engine as the IS 250, the 4GR-FSE, that was compatible with the AWD system in the car. However, the new 2.0-liter turbo 8AR-FTS engine would not work. So, instead of reconfiguring things to fit, or simply omitting an entry-level AWD model, they took the less expensive route of detuning the 3.5-liter 2GR engine. That way, if a buyer should pay for the 350 AWD, they would get a boost in power over the entry-level 300 AWD. The 300 AWD simply took the place of the discontinued 250 AWD. Simply put, it was a way to create different power and trim levels. The 2GR-FSE and 2GR-FKS engines are mechanically identical between the 300 AWD and the 350 models - the only difference is the tune.

 

Likely because the module responsible for sending torque to the front wheels cant handle 280 torque... So, the lexus engs decided to detune it slightly to meet their internal reliability / failure rates. That would be my guess.

What supports this is the fact that 2015 is300 v6 has identical power/torque curves up until where that torque might become a problem after which it gets knee-capped. which is very obvious from this chart.

 

I've heard this theory before, but I don't buy it personally. What, do they manufacture transfer cases/ECUs/TCUs to different specifications depending whether it's a 300 AWD or 350 AWD?

I heard a theory once that engines/transmissions that can't handle the full power get sent to the 300 AWD pile instead of the 350 pile...

I'm still sticking with my theory that there's nothing mechanical separating the drivetrain of the IS 300 AWD from a 350 AWD, and it was purely a convenience choice on Lexus's part to de-tune the engine to create a new trim level. For what it's worth, I don't think your average owner would even feel that torque difference unless they knew where in the RPM range it was. When I drove a 350 AWD, I could feel it, but I already knew it was there. Honestly, the 300 AWD is pretty quick for a "base engine" car. Just tune it if you need 300+ horsepower.

 

i mean, it is a possibility too, but since toyota has "you pay for it, you should be able to use it" mentality (unlike tesla), detuning it simply for creating a non-competing model to is350 RWD sounds less possible.

It looks like A760H was in use since 2005 - they still use the same tranny for 6 speed awd versions of the IS300/350 today.
However RWD AA80E was in use since 2007 and its derivative - AA81E - since 2013.
There is no updated AWD version either for a760h, or for AA8X tranny, which indicates that Toyota simply did not bother to develop a new AWD version of it to handle higher torque. Instead they ended up using the one from 2005..

Since the requirements for torque were different in 2005 for that awd light-medium torque tranny, compared to what was expected in 2014-2015, I think it is reasonable to assume that a design limitation has its place in a760h, and toyota simply works around it by knee-capping v6 engine in is300 model, that otherwise would have exceeded what that tranny can handle within its set reliability margines. Could it handle 280 torque? absolutely? Could it handle it for 15 years? Probably not.

So, instead of spending millions on developing a new version, they slightly detuned it and called it a day.

 

Anecdotal evidence, but I had a 2021 IS300 AWD F-Sport as a loaner and its 0 - 100 kmh (0 - 60 mph) felt exactly similar to that of my IS350 AWD F-Sport. I tested this multiple times in auto Sport S+ and manual Sport S+ modes. It is likely that the IS300 AWD is made to short shift earlier than the IS350, and the gap between the two will widen as you redline through gears 3 - 6.

 

In my experience, all IS's will short shift a bit unless I use manual mode... except perhaps the IS 500. I pinned it in that car, and it went all the way to about 7000 in first gear.

However, yeah, the power difference between the 300 AWD and 350 is in the top of the powerband. Peak power is still over 6000 RPM in both cars, but the torque gets cut pretty hard just before 4500 RPM in the 300, and it never really gets back up to that level again. The 350 is allowed to continue building until it reaches peak torque around 4800-5000 RPM. If I am looking for it, I can feel that torque dip in the 300 as well as the peak in the 350 - in fact, that peak is one of my favorite things about my 350, like a reward for finding the opportunity to reach said RPM. As you said, it's a subtle difference, to the point where someone would probably say they feel the same, that is, until you get into higher gears and spend more time in that high-RPM range.

 

If your just daily driving not noticeable . Coming from 2nd gen is350 rwd to is300 awd top end where is slower to get moving with W.O.T . but I talk to tune by Loi if any body close to the Bay Area Cali. He can see if it tuneable to get the power back to Is 350 status. From there he will see if it can be remote tune by him or need to be in person. If remote tune them that open the door for a lot of us. I rather not have it like RR where you have to be in sport paddle and traction off to utilize it.

 

To cut their costs, it was cheaper to take the 350 and cut down the costs (delete the ML audio and AVS [to reduce costs], plus de-tune the engine which does not cut and costs but was necessary on their end to further differentiate the price differences between the 300 and 350) instead of spending a lot of time and money on re-designing a new AWD variant IS for the lower price segment. What was one of the factors that triggered this?, the fat 6 speed transmission needed for the AWD.

 

But the IS 350 AWD still exists in the product lineup.

 

Because they need a entry level AWD option to compete with MB/BMW/Audi; and it's cheaper to detune the drive train they already have, rather than develop a whole new AWD 2.0T powertrain. MB did more or less the same thing with the last generation C300/C350. As well instead of having 20 different flavors of the 350, with the 21+ the 300 is positioned as the 'luxury' entry level, while the '350 FS' is the sport entry level.
I have a IS300FS with the RR racing tune & a 'stock 350 tune'; and I borrowed the the 21 250FS for about a month this year. The stock 300 and the 350 feel identical power wise around town. On the highway though, the stock 300 dies at ~4K RPM while the 350 or tuned 300 keep on pulling till redline. It's definitely noticeable but not world changing. It felt a little faster with the tune on, but I really felt the difference driving around with the 'stock 350' tune for a few months then switching back the stock 300 tune.