Question for the engine gurus out there...
 

Why is it that when I launch (WOT) from a standstill the revs go to 6300rpm or so (which is fine) but then drops down to 4700 when it shifts to 2nd gear? and the same when it shifts to 3rd gear and so on?

There are a couple of guys on Youtube that are pulling mid to high 5 seconds on 0-60mph runs with their bone stock GS4's. I noticed on their cars that their rpms only drop to maybe 5100rpms when shifting to 2nd and the same with 3rd...what gives with my car? Why can't I keep the revs high(er) like that?

I'm sure that I am quicker with my current mods than a stock GS4, it's just that I feel like I'm not get there as quick as I should because my RPM's drop around 400rpm more...which at ever gear shift makes a HUGE difference when "driving enthusiastically".;) What do you guys think?

Simple things to check:
-Be sure you have pwr mode selected.
-Reset your ECU

maintenance items:
-Get better gas-try a bottle of fuel system cleaner
-change air filter, clean MAF, and throttle body (reset ecu again)

Did you change the gear ratio? SupraTT rear end?

Yes, I have done all of these things and then some...:sad:

...yes, I have changed the rear to the Supra TT rear. How does that change the shift points of the car?:uh: I would think the shift points stay the same since I just change the rear (all mechanical). How would the car's electronics know if I put shorter or taller gears in the rear. I am NOT making adjustments to the transmission at all. I do have the Precision Industries torque converter but I don't see how that would make it drop (rpm's when shifting to the next gear) moreso than stock. It's as almost if something with the timing? Please explain if you think otherwise...Obviously I know you know a lot about cars Jeff. I just need clarification.:thumbup:

I also have the 3.76 Supra TT rear in my car so that should put us at the same gear ratio, but I do have a pretty high stall TC. I'll have to go drive around in my car to compare. I shift at close to 8000rpm and my rpm usually drops to around 6500-6800rpm after each shift. I'll get back to you when I find out.

Have you checked the simple stuff such as:

Are they manually/gate shifting the car? If so you can rev it out further so it would appear that the car is shifting faster.

Possibly they have tiptronic? I don't have tiptronic in my personal car but it could possibly be giving them a few more rpm, similar to gate shifting the car.

your car is either
a. fine and you just imagining things, because the only thing that can change on how far the rpm drop after the shift is the transmission gears.
b. Your stall converter it tighter under load while accelerating(which is better anyway) and the other peoples stall or trans slips a little alowing the RPM to stay higher after the shift.

I have tiptronic (e-shift) on my GS4. The guy on youtube did not have his in manual mode; it was just in regular drive. I compared mine in the same fashion and mine (rpm's) drops lower than his after each shift.:uh:

...this could be it. However, I don't know THAT much about TC's to know the effect it has on how the transmission shifts.

FYI...It's NOT that his car rev's quicker or shifts quicker; it STAYS higher up in the RPM range throughout the shifts. Maybe I can find the video and I'll post it up.

I will check on my stock LS400 for recovery point after shift (same engine and gearing as GS400)

Couple of things come to mind. When you change your gears the ECU gets different RPM vs MPH information. One known result is the top speed limiter drops from 149mph down to around 128mph. It is possible other things are effected such as torque converter lock up. Maybe the stock setting unlocks the converter on shifts to improve performance and reduce locking clutch wear/tear. Perhaps with the gearchange this unlocking no longer occurs and your converter stays locked. Just guessing of course but something must be going on.

I think that it is electronically limited to 149mph with the stock setup; meaning you could go faster mechanically speaking if you remove the electronic limiter. As far as changing the gears to 3.76 or 3.92 I feel that you are mechanically limited to 128mph...it will be maxed out at redline in overdrive due to the gears nothing having to do with the electronics limiting it. I could be wrong though but it is logical to me.

Let me know what you find after taking your LS400 for a spin...thanks.:thumbup:

i understand exactly what your saying about your car theres only a few things that can cause that, transmission gearing different (which is very unlikely) Stall converter locking/unlocking like the person before me was saying. ITs posible your converter is staying locked at all times, it usually should only lock in O/D 5th gear in your case. That could be converter itself or transmission ECU.

Putting in the 3.76 rear will still allow a top speed of 177mph at 6500rpm. I have the same 3.76 rear end gearing but rev the engine to 8000rpm which should technically net 218mph in 5th gear at redline.

Taking into factor of a stock A650E transmission gear ratios you will get approximately the following speeds:
3.23 GS4 stock gearing will allow a top speed of 206mph @6500rpm in 5th gear
3.76 gearing top speed of 177mph@6500rom in 5th
3.92 geairng top speed of 170mph@6500rpm in 5th
4.27 gearing top speed of 156mph@6500rpm in 5th

Thanks for the response. So, how can I tell if the TC is staying locked all the time? If it is staying locked at all times is this a malfunction with this part?

Regarding the tranny ECU...wouldn't I get a different CEL code for that? I always check (and just checked this morning) my tranny fluid, it's bright pink (like I just changed it yesterday) and at the full line when hot (after driving for 20 minutes).

The reason why am mentioning this is because if the tranny ECU was the culprit and making my car shift erratically wouldn't it burn up my tranny fluid and brown it? The fluid seems to be fine especially since I havn't changed it in 2 years. Amsoil synthetic ATF FTW!!!:thumbup:

Nice work Jeff! I stand corrected! I had no idea our cars "could" be capable of that.:eek2:

I looks like Lexus limits the top speed by limiting RPM in top gear.
5th gear with stock gearing = 149mph at 4650rpm.
The interesting thing is that stock gearing at redline (6300rpm) in 4th gear = 153mph :uh:
With the Supra 3.769 ratio the electronic limit of 4650rpm = 125mph.
Redline in 4th = 127mph.

My LS400 drops from an indicated ~6200rpm to 5000-5100rpm 1st to 2nd shift.

If your torque converter is staying locked that should not be due to the torque converter itself but rather the signal to lock/unlock from the ECU.

If this is happening it would not cause (in and of itself) other tranny problems.

Another thought is how quickly your transmission shifts. Stock shifting is slow. During this transition there is load applied and by the time the shift is complete the resulting revs would probably be higher that a quicker shift that pulls down on the engine more quickly. Cars with the PI torque converter tend to shift more quickly. Again, something is going on here.

...what should I do J?

-I can't bring it to the dealership (who supposedly knows all about Lexus vehicles) because they would say they can't "possibly" diagnose the car due to the modifications.

-I cant's bring it to a local shop because they may not know how to fix this particular issue due to my mods.

This is the annoyance of modding because if an issue should arise it is hard to decipher which mod is causing the problem.:sad:

I would PM other PI converter owners and ask them to test their RPM at shift points. It may be a common instance when running the converter and or converter 3.769 gearing combo. It may not be anything worth worrying about. BTW, have you been to a track or done any measured runs, 0-60 and or 1/4 mile?

No, the nearest track is about 2-3 hours away.:thumbdn: Also, it wouldn't even be fun because I NEED wider, stickier rears for traction in order to obtain proper figures of the car's performance.

I contacted Derrick from D2 Autosport and I am looking into the Forgestar F05's (19X8.5 front / 19X10 rear) w/Toyo Proxes T1R's (275's in the rear). Those wheels are only 22.5lbs each!:eek2: A net savings of 7lbs per corner from my old (now sold) cast aluminum 19's.:thumbup:

I will try to PM a couple of members with my setup as you suggested. Thanks.:)

Usually you can tell when you in 5th gear and you are crusing when you hit the gas just a tad bit harder it feels like youre in 5th gear driving a manual tranny car, thats the best way i can explain it to you. Like it has no give when you beraly tap the gas without converter unlocking in O/D you feel sorta joult from the drivetrain it might be hard to feel in a smooth car like a GS though. you can also watch it shift when you drive it, watch rpm drop from 1st-2ndto 3r4d-4th and then pay attention when you get to 5th watch it shift and then keep an eye on it and you should see rpm drop like another 200-400rpm after it shifts into 5th that means converter just locked, if it dosent do that its either
a. not locking at all
b. locked all the time
your Trans Ecu could be bad in a way and you might not be getting a CEL, you wont always get a CEL if something is wrong, i have seen cars run missing 2 cylenders and cel wont come on.