98 VVTi transplant into 91 LS400 - Hitting rev limiter.

[Spinnetti]

I think I may know the answer, but not the solution.

I did a transplant and it runs and drives fine. I also swapped in the Ring and Pinion from a 98 SC300 (and a Supra Torsen LSD) to get a shorter final drive (3.26 to 4.27) and am running smaller diameter tires too, all to make the car quicker off the corners at the race track.

So what happens is sometimes it will bounce off the rev limiter and not shift. I'm assuming the ECU/TCU is using a calculated speed rather than actual speed.

Do I need to correct for the final drive ratio change for the car to shift properly? Just guessing, but is there a speed sensor on the trans and I need either mechanical or electronic speed sensing correction? (I hope that's all it will take). Just in case and because it had lots of miles, I had a race transmission built with more/stronger clutches and all that, but it still hits the rev limiter before shifting sometimes.

Any easy fix?

 

[George_R]

Get a modified valve body for quicker shifting

 

[Spinnetti]

I have a fully race built trans, and both it and the original stock trans did the same thing... its not about speed of shifting - its like the ECU can't process the difference between the engine RPM and expected transmission speed or maybe that the ECU only cares about engine RPM? Either way, it doesn't shift at the right time, and I was assuming it was because of the transmission shaft speed being different than expected.

 

[gloverman]

Are you using the A650? From memory of your car its a 1uz vvti swap? Options are an aftermarket ecu or stuffing around with the two transmission speed inputs to give the desired results.

 

[Spinnetti]

Yes, 650.. The engine and trans both came out of a 1998 GS400 as a pair. I'm trying to validate if changing the rear end ratio could cause shifting issues, and if so, if there is a circuit I could add to the speed sensor to compensate for the gear change.

 

[gloverman]

Yes, 650.. The engine and trans both came out of a 1998 GS400 as a pair. I'm trying to validate if changing the rear end ratio could cause shifting issues, and if so, if there is a circuit I could add to the speed sensor to compensate for the gear change.

Understanding how the transmission selects gears and gear change logic via load signals one of which is the output speed signal might be a good way for you to increase your knowledge and as such answer the questions you have. (which is of coarse yes changing the diff ratio alters the gear shift points relative to the vehicle speed)