I believe RMMGS4,

BTW, there are 2 limits on US specs car, depend on which one you hit first:

-RPM limit, ie redline
-Speed limit

I don't think you have any problem from changing to the 3.76gear with the speed limit, except you are hitting the REV limit (RPM limit due to the higher gear)

Maybe, the lexus speed and rpm limit were set very close to each other, that is why you get confuse, thinking that you are losing top speed, but in reality, you have just lower your redline (in a sense, because your engine rpm is closer to redline in every gear ) a bit, and when over in the redline in 4th gear (are you? Not sure which gear you are hitting, my guess is you are hitting 4th)

if you can raise your redline just a bit, you will make it to 5th and you are back to business then you will hit your SPEED limit like stock GS.

 

???

If you follow the direct connections from the engine to the wheels you will always have a direct correlation between the RPM of the transmission and the RPM of the wheels. Doesn't matter if you're running uphill in a tornado. The load on the engine may go up but the rotation stays the same. The speed would always be measured right at the output shaft of the trans which has a fixed ratio to the rear diff.

Now, if one of you're wheel is free-wheeling (ice, etc..) then you don't. In "old fashioned" cars I used to drive 50-60 MPH while getting out of a snow-bank!

So I guess I don't understand your point here. :shrug:

 

If you follow the direct connections from the engine to the wheels you will always have a direct correlation between the RPM of the engine and the RPM of the wheels. Doesn't matter if you're running uphill in a tornado. The load on the engine may go up but the rotation stays the same.

that is due to the transmission.

Going back to the 3.76 gear, that is external to the transmission

You can measure your the engine RPM, even that they are pretty linear, but you can't figure out the speed of the car, that is my point, the engine loading and transmission gear rotation totally mess up your speed calculation. That is why the ABS sensor is needed. And by changing the 3.76 gear, it's external to the engine and transmission, there is nothing the engine can do to recalibrate this, since the engine does not based their speed (mph) calculation on the engine speed or transmission rotation (I sure It can be done, like the Gtech, but that is not perfectly accurate, and does not account for wind speed and road condition...)

Stick with the good old ABS sensor, then you have truth speed (mph)

 

Hmmm, never checked on what gear I was in in when I bounced of the rev or speed limiter limiter. I am pretty sure it was in 5th gear. Sounds as if I might have to go out and do a test.

But I agree with most here in that I much prefer the lower punch out of the hole that the new gearing provides.

 

I guess I misunderstood your comment previously. You seemed to indicate you couldn't understand how the transmission output shaft could measure speed. I was just stating that (so long as you don't change the diff ratio or one of your wheels isn't spinning) it worked great!

While the ABS sensors are good, even the ABS sensors will get it wrong if you change the assumption about the overall diameter of the wheel.

Sorry if this is off-topic.

 

Hey this is important to me. I am considering getting this modification and I want to know if the top speed is really going to be reduced. It really doesn't make sense to me, as my calculations show that the top speed should still be 150mph at about 5600 RPM in 5th gear. My chart also shows that in 4th gear you should be right at 130mph when it hits the red line. However, the RPM for 150 MPH with the stock differential in 5th gear is the same RMP at 132 mph in 5th gear with the RMM gears. Hope you were in fourth. Check it out and let us know. I want the pick-up and the top speed!

 

guys...tonight i did a test.
i took my 2001 GS430 WITH SUPRA 3.76 LSD and my 19 inch 245 front 275 back rims/tires. up to about

133 MPH, same as what PEARLPOWER tested.....
at 133 mph, the RPM was AT about 5000 rpm and it just wont go any more...
BUT i "think" it was at 5th gear...not sure though..but maybe

is there a way to still go up to 145 mph or even 150 mph??
modifications??

BTW i took my 2001 GS430 with 17 stock rims up to

150 MPH for several times... and it just won't go any higher..

 

If you were going 133 mph and hitting about 5000 rpms you were in 5th. Too bad! I had hoped that the car would still get up to 150 mph with the RMM rear. Oh well! At least it is fast off the line!

 

If you can't beat them by 133,,then no sense in going higher. Besides, 99.9999% of my run-in's are over way before then.
You just cannot beat the low end the gears give. Picked up new 265/40's and they just spin like a top from the line when punched. When my new camcorder gets here, I'm going to really test the rubber.
Keep it safe.

 

Ok, I think Bananna doesn't understand what is being stated on correlation of rear end gear ratio to tranny outputshaft speed... Also, this statement is incorrect:

If you follow the direct connections from the engine to the wheels you will always have a direct correlation between the RPM of the engine and the RPM of the wheels. Doesn't matter if you're running uphill in a tornado. The load on the engine may go up but the rotation stays the same.

From the ENGINE to the wheels does change, with whatever gear the tranny is in. But that's nothing to do with speed sensing.

From the tranny's OUTPUT shaft, or basically, the driveshaft to the wheels, WILL always be the same. The output shaft of the tranny is where the speed sensing happens, thereby making that the same ratio, to whatever speed the wheels spin. The only way this can be altered, is with the gear ratio in the differential, or with higher/lower tire profiles, in relation to the wheel size.

SO, if you go with a higher gear ratio in the differential, like switching to the Supra Automatic diff, the output shaft spins x amount faster at 55mph than it used to. The output shaft sensor then thinks that the car is going faster, and shows a higher MPH than what you are really going. EXCEPT in the case of "smart" cars like the Lexus that uses the ABS to also correct.

The ABS sensors can also be confused by large differences in tire profile, so basically, if your stock tires are 21" tall (16" wheel, with 5" of additional tire depth) and you then put 15" wheels, with say 2" of tire depth, your speedometer would then be off a bit.. Saying you are going faster than you really are. More error the faster you go. If you go with really tall wheel/tires, then your speedo would say you are going slower than you really are, so watch out for smokey then...

By the way.. the quickest and best way to see how accurate your speedometer is, would be to borrow a GPS.. My buddy has one with maps of the USA, that he uses in his airplane, to help him navigate, and it shows true MPH based on time and distance covered.

 

95sc300t: I agree with you 100%. In fact if you read my *original* post you'll see that's what it says. Banana quoted my post while I was in the middle of editing it (after noticing my original mistake). He's just too quick with the reply...

 

OK, good.. 'phew" I was just making sure people wern't under the impression that engine rpm's somehow had something to do with the speedometer...

Now, I can't believe that nobody has looked into finding a hack to overcome this top end speed limiter... On a Suzuki 1300 Hyabusa, (A 200mph bike) its a VERY simple matter to disable the 170'ish mph speed control.. But, if the Lexus has it built into the CPU, then we might need a way to feed it false information about speed once we reach 130+mph, and go by the tach to know how fast we are going.

Of course, I'm not usually in THAT much of a hurry to get places... But if one were to goto a Solo1 race, 140 or so mph would be standard.. at least I was going that fast back a few years when I ran my Eagle Talon on the airport runways at Stapleton airport in Denver.

 

What kind of performance gain do you get from the new rear end? Has anyone done a 1/4 mile test? 0-60? Thanks.

Rob

 

My best 0-60 is 5.3 using a G-Tech, but that's including an upgraded TC. I will be taking the car to the strip once the season opens. At the track I hope to hit 0-60 in 5.2 sec and 1/4 mile should be in the high 13s depending on driver skill.



Regarding this speedo thing, I have read conflicting reports on this thread and previous threads over the past year on how speed is sensed on GS models, not SC, LS, etc.

Who can confirm "without a doubt" if the speed is measured off the tranny or the ABS sensors?

 

so the 0 to 60 mph WITH the SUPRA LSD only will be..????
5.5s???

someone can clearify this??