How much more green would it take to get around this? No use building power you can't use...

 

I'm at 400 rwHP and NEVER had this rev limiter problem from 3 to 4 @ WOT. I'm sure there are plenty of factors & variables between Morris and my set up that could explain this.

As for my tranny, I've got the valve body mod, a TC with stall set up for FI, tranny cooler, plus synthetic Amsoil probably doesn't hurt. Other than that, no other tranny mods. Another factor is my LSD which is stock geared instead of the TT 3.76 that many use. All these variables can be a factor in preventing rev limiter bounce.

If DaveGS4, Veritek or speedaddic can chime in on their FI / tranny shift experience, that would be a good set of data points.

 

if i recall correctly, he has a majority of the same mods you do. fully rebuilt trans with VB mod, 2800 TC and stock geared rear end with TRD lsd. also if i recall correctly, he said he didnt have these problems when he was supercharged...only after he went turbo.

i dont know exactly the cause or the problem, im only repeating what i read in his build thread. search his username and you all can read the same things i did...

 

Hey RMM, have you ever tracked your car (i.e. drag strip)? If so, is your car capable of 12's in the 1/4 mile @ your 400whp (supercharged)? I would like to know.

It MAY be worth it down the road to keep my car forever as a weekend car and make it the fast leasure weekend car I always wanted to have (by doing some FI work). If I find that $10K is better used towards a different weekend car then I would go that route.

 

I too have read of people hitting the rev limiter with an FI GS. But, if you knew your car is DEFINITELY going to do this why not just shift manually with E-Shift (assuming it is a GS400) right before redline everytime? Wouldn't this be a solution?

 

^^ i was thinking the same....but from the sounds of it, the transmission ecu cannot keep up with the rev's of a turbocharged motor. from my research, since a supercharger makes more boost as the rpm's climb its much easier for the transmission ecu to keep pace. a turbo makes peak boost early (say 2800rpm) and holds that to redline. a car rev's out MUCH quicker that way. i have dyno'd a few supercharged honda's and the powerband mimicks the n/a power band. ive also dyno'd lots of turbo charged cars and the power band is much different.

personally i dont think the problem is in the hardware (trans, valve body, TC etc) i think its in the programing of the trans ecu....

keep in mind this is all hearsay because i dont own a boosted gs......lol

 

This is an excellent report. Great to have you on this forum

I am not a fan of reporting second hand information but that is in fact what I was doing. To be fair I believed my sources to be accurate (Unichip a few years ago and others) and the theory was sound.

I am still curious on why the "theory" is not holding up in your application. Theory goes, adjusting the MAF signal so that the stock ECU leans the mixture to acheive the desired A/F ratio.

Question: does the SAFC-II only operate at wide open throttle (WOT)?

If so, that could be why the stock ECU does not try to compensate. Otherwise leaning the MAF under all conditions SHOULD eventually be compensated as the oxy sensors would report a leaner that targeted condition.

Interesting thoughts you make regarding boosting at part throttle. Conditions could be significantly different between supercharging and turbocharging regarding part throttle boost as well as boost/power profile during shifts.

On shifts one of the "smoothing" parameters is the stock ECU retards timing. On a supercharged engine that has a fixed flow vs rpm condition this would lower power whereas with a turbo the energy from retarding the timing flows into the exhaust manifold which could increase boost depending on the wastegate. Other variables apply but a tranny that is "almost" over revving in a supercharged 400rwhp condition could go over the threshold with the same peak power but turbocharged causing more power just prior to the shift.

 

with all the ecu's ive worked with in the past, anything over aproximately 70% throttle sends the ecu into predetermined maps. (open loop) since thats the case, the safc works perfectly since those maps give the same amount of fuel everytime you mash the throttle. after i installed the wideband, WOT was the only area i was concerned with (10.5:1 afr's on an n/a motor arent ideal lol)

honestly this is the first time i have ever ran an safc on my own car as well (ever lol..i usually run chipped ecu's or full stand alones)...so the abilities of the safc are still new to me. although since many other cars run maf's and safc's i would say that they work. as far as the ecu "re-learning" i dont see how the lexus ecu differs from other maf type ecu's. all cars that run in closed loop conditions try and adjust the afr's. these cars work fine with safc's....as should ours. take Morris for example....he ran great with an safc as his only tuning device, making what, 500+whp? (iirc)

i really dont see it as a problem...just need to do it for myself so i have a better idea of how it all works.

 

I am still working on my set up before I do some 1/4 mile runs. Launching is the big problem with the GS. I did a few 1/8 mile runs, but never left hard off the line, since the day I ran it was very hot and I have very low profile (25 series) tires, so I never could go WOT in 1st gear. I'm contemplating to get some street drag slicks, just to see what the car is capable of.

 

Yeah, tell me about it...I'm on brand new 275/30 (on 19 X 9.5 wheels) super sticky Bridgestones in the rear with around 120lbs of stereo in the trunk and I STILL spin 'em at a launch on the street! and that's without FI!

What would you suggest me do for better traction? I was thinking of getting rid of my stereo equip to strip some weight. Is there anything I can do with my suspension? Such as bring it up a little in the rear...would that help? Do they sell traction bars for our cars? How do they work? I know the simplest would be to let some air out of the rear tires but I am not running a few passes on a track where I can fill them back up - I'm just having a little fun on the street.

 

the simplest solution is to buy another set or rims and have some drag radials/slicks mounted on them. you will not, get any sort of traction on street tires...espescially running a higher stall. nature of the beast.

 

I agree.. with your power you are most likely just spinning the tires. Drag slicks make a worlds of difference. But I know you are street so its only really practical at the drag strip..

Traction bars were designed for cars with a live rear axle, like on a chevelle or camaro. We have independent rear suspension.

 

I was going through some old e-mails, and the Mahdavi motorsports turbo is going for $7,000 installed. (That's an old quote, though...may've changed.) Anyway, that doesn't seem bad. 415 rwhp, all parts researched and installed...

 

Even better if it includes tuning! Good price though. I thought I saw a kit going for over $15k alone w/o install.

 

Hey Jbrady, just wanted to addresss your Question:
does the SAFC-II only operate at wide open throttle (WOT)?

From my past boosted experience, you can set the SAFC to operate/intervene at any %+ of throttle position you set it at. Lets say you set to 70%, and it sounds like that is basically the threshold of open loop operation for the GS. This 70%+ would be the only time you would want the SAFC settings to begin modifying the MAF signals going to the ECU.

Someone on here commented on not liking FMU's, saying with all the new tech available why go that antiquated mechanical route. I think they work great on return fuel systems when paired/fine tuned with an AFC device and of course using a higher pressure 255lph fuel pump. Not to mention you can usually get away with stock cc/lb size injectors for boosted ~100hp over stock applications. This stock injector size allows good, closed loop & low-throttle, idle and fuel economy, as there is no intervention. I mean really why overcomplicate it with a $2k+ standalone and $$$$ in tuning hours on the dyno if you can get it done safely and with similar power results with a FMU/SAFC combo?

After thinking a little more about this, Maybe this all gets more complicated with the earlier ~3k boost surge you get with Turbos, versus the much more gradual Centrifugal Supercharged boost, I have experience with?