Torque Converters

[jerrysta]

Guys, now that I have some other mods done I am looking at torque converters. One thing not listed in my sig is that I have ordered a set of drag radials that will fit my old rims to use at the track. I'm looking for the best way to increase my 1/4 mile time.

I still want the car to be very friendly just to drive around town. Will a torque converter have any negative affect to the driveability of the car? Another concern is the rear end. I have recently switched to 3.73 gears and am wondering with sticky tires if I will blow up the rear if I add the torque converter?! There really is no engine mods other than CAI, so the power is near stock.

Most importantly, what is the best stall speed for our LT1's?!

[N20LT4Bird]

It really depends what the stall speed is set at.......if youre just adding a few hundred RPM more stall for a harder launch, then driveability wont suffer too much at all. A higher stall speed puts your car's engine into the power band off the lauch. That combined with some sticky tires COULD smoke the rear. The automatic is still much kinder than the M6 on the rear end though.....if your HP is near stock, then you'll probably be OK.

[jerrysta]

Thanks, any ideas as to a good stall speed for our lt1's?

[95TransAm]

If you want it still nice and street friendly, then I'd say 2000-2400 stall.
If you want it more track friendly than street friendly, but still not too bad, I'd say 2500-3000. Once you start going past 3000, it can start to be a little unfriendly for some on the street.

Hope this helps

[jerrysta]

So 2800 would be good? How exactly does one of these effect street driveability? Thanks.

[95TransAm]

A 2800 stall converter wouldn't be bad for street use in my opinion.

When it comes to affecting your street drivability, all it's doing is making your car put its power to your wheels at a higher RPM. So when you hit the gas, if your touch is light, don't expect to start moving as quick as you once did. You'll hear your motor rev, then you start moving. The advantage, of course, if your launching in a part of your RPM band where there's more power. The same goes for reverse as well.

Get used to not having to apply the brakes at stop lights if your on a slight incline, or if one of your wheels is in a rut/small pothole, etc...

[fastTa]

If you want it still nice and street friendly, then I'd say 2000-2400 stall.
If you want it more track friendly than street friendly, but still not too bad, I'd say 2500-3000. Once you start going past 3000, it can start to be a little unfriendly for some on the street.

Hope this helps

This was true on most of the older converters, but with today's converter technology, flash stall speeds over 3000 are not bad at all on the street. I had a Vigilante 4200 (actually flashed to about 4100) in my 97 TA and it was just a bit soft getting going, but after about 7-10 MPH it was not bad at all.

Older converters suffered from turbine wash really bad because of the turbine design and front cover design and increased rotating mass of the turbine, stator, sprag, and clutch assembly.

Older technology converters were also using clutches that were not designed to work well with the OBD-II technology that incorporates a technology called "Pulse Width Modulation". This is a technology within OBD-II PCM's which does not allow the converter clutch to lock up 100%, but instead just 99.5% locked. Newer converters have special clutches made from carbon-fiber that is designed to work well with PWM OBD-II systems on automobiles. The PWM system was engineered to assist in smoothing out power transfer from the inherant intermittent pulses from the ignition by allowing that 0.5% percent slippage in the lock-up clutch.

So basically with these revised torque converters for the PWM systems, they are better suited for higher stalls on the street due to their design which allows for a more efficient transfer of low RPM power.

One thing to note that is of significance when going with a larger stall in conjuction with a 4L60E is the common problem of the TCC (torque converter clutch) regulator valve within the 4L60E valvebody that regulates the flow of fluid into the torque converter. It is a common problem for the TCC regulator valve to wear out the bore in which it slides in. This allows some bleed-off to occur and the resultant effect is a loss of pressure potential to apply the converter clutch properly. This can cause the converter clutch to slip more than it normally would at lower RPM's when line pressure is unfortunately lower than at higher RPM's. It can also wreak havoc with the lock-up procedure in 4th gear as well.

When this bore gets worn out and causes the converter to slip, the PCM sees this because it knows current line pressure, TP position, engine speed, the 4L60E gear ratio, and the VSS data (Vehicle Speed Sensor). The LT1 PCM will then apply maximum line pressure to prevent the clutch slippage. You will usually see code P1870 if this continues to happen.

I would reccomend addressing this issue while you have the tranny out just to make sure your new converter will not have any problems. TransGo offers a shift kit for the 4L60E called the 4L60E-HD2. It includes an upgraded replacement TCC regulator valve that is supposed to stop this problem, but does not address the damage caused to the bore. Even though, people have often said that this shift kit does indeed fix the problem.

If it were me I would purchase a kit from a company called Sonnax. It includes an oversized valve and a reamer to essentially re-hone the valve bore.

http://www.trannytools.com/sure-cure/sure-cure.htm

[95TransAm]

That's why I love these forums, I'm always learning something new
I'll tell you right now jerrysta, that I know a decent amount when it comes to automobiles, but people like fastTA, Injuneer, wolfman, Joe1320, performin normin, and the more experienced guys know a lot more, and I would take their advice anyday.

Older technology converters were also using clutches that were not designed to work well with the OBD-II technology that incorporates a technology called "Pulse Width Modulation". This is a technology within OBD-II PCM's which does not allow the converter clutch to lock up 100%, but instead just 99.5% locked. Newer converters have special clutches made from carbon-fiber that is designed to work well with PWM OBD-II systems on automobiles. The PWM system was engineered to assist in smoothing out power transfer from the inherant intermittent pulses from the ignition by allowing that 0.5% percent slippage in the lock-up clutch.

Just a quick question to this though. According to his sig, he has a 95 which equals OBD-I. I'm assuming that "Pulse Width Modulation" technology isn't incorporated in OBD-I, or am I wrong?

::EDIT::
I should have stated it earlier, but I 100% agree with the idea of getting a shift kit....it's more than worth the $$$.

[fastTa]

That's why I love these forums, I'm always learning something new
I'll tell you right now jerrysta, that I know a decent amount when it comes to automobiles, but people like fastTA, Injuneer, wolfman, Joe1320, performin normin, and the more experienced guys know a lot more, and I would take their advice anyday.

Just a quick question to this though. According to his sig, he has a 95 which equals OBD-I. I'm assuming that "Pulse Width Modulation" technology isn't incorporated in OBD-I, or am I wrong?

::EDIT::
I should have stated it earlier, but I 100% agree with the idea of getting a shift kit....it's more than worth the $$$.

Yes, OBD-I's had PWM as well. To the best of my knowledge all 4l60E equpped cars had PWM. The 700 R4's did not.

One more thing I forgot to add was that it is possible to completely "delete" the the PWM from the PCM. This should only be considered a last resort fix though in my opinion.

[95TransAm]

Yes, OBD-I's had PWM as well. To the best of my knowledge all 4l60E equpped cars had PWM. The 700 R4's did not as they had a solid lock-up TCC.

Ah, then with this knowledge, a higher stall wouldn't be too much a problem as I originally thought for street use. I needed a tranny when I got mine done (due to the fact that mine original tranny was done with completely), and literally spent all my extra $$$ on beefing it up, gettin a shift kit, and going for the highest stall I could. Unfortunately for me, the highest stall i could get was 2400...and that's what went in. So the only experience of a higher stall I have for a 4L60E is mine.

My experience on higher stalls comes from a 700R4 and a TH-350. The 700R4 had a 3000 I believe, and the 350 had either a 3000 or a 3200. Both were quite rough on the street might I add. Nothing I didn't have an extreme amount of fun with of course , but rough for the daily driver I would assume. I guess that would be the reason why I didn't even know Pulse Width Modulation Technology existed.

Thanks for the info Kevin....I'll keep that in mind when I buy my next converter

[fastTa]

My experience on higher stalls comes from a 700R4 and a TH-350. The 700R4 had a 3000 I believe, and the 350 had either a 3000 or a 3200. Both were quite rough on the street might I add. Nothing I didn't have an extreme amount of fun with of course , but rough for the daily driver I would assume. I guess that would be the reason why I didn't even know Pulse Width Modulation Technology existed.

Thanks for the info Kevin....I'll keep that in mind when I buy my next converter

You are not the only one. Many of the posts I see and people I talk too that say "Oh man, anything over a 3000 is crazy on the street! " usually have never driven a 4l60E equipped car with a fairly large stall (3400+). So they are just basing their knowledge on 700R4, th400, and th350 equipped cars. Nothing wrong with that they just didn't know.

[jerrysta]

Thanks a lot, man. I am such a novice that I only understand part of what you said. But thanks. This is how I'm learning, so again thanks to all of you!

I have the option of purchasing used with low miles either a 2800 stall or a 2400 stall and want to be able to decide which one would be best.

Let me see if I have this right, okay. When I hit the gas I will have less throttle response but once the car hits the stall speed it will come on a lot harder?

[fastTa]

Thanks a lot, man. I am such a novice that I only understand part of what you said. But thanks. This is how I'm learning, so again thanks to all of you!

I have the option of purchasing used with low miles either a 2800 stall or a 2400 stall and want to be able to decide which one would be best.

Let me see if I have this right, okay. When I hit the gas I will have less throttle response but once the car hits the stall speed it will come on a lot harder?

A larger stall will in no way affect your throttle response. In fact with with a larger stall it will actually feel as if your throttle response has improved.

Just think of it this way. The larger the flash point (stall) the "looser" the torque converter is. This allows you to nail the gas and have the engine rev while building inertia up until the point when the torque converter reaches it's flash point (stall speed). When the converter reaches it's flash point the pump(front half of the converter) and the turbine(back half) become hydrostatically locked by means of a viscous liquuid (trans fluid). The actual flash point will also of course depend on the power level capable of the motor, specifically the torque load potential.

Sounds fancy, but all this means is that the larger the torque converter's rated stall speed, the more "loose" it will feel. Sort of like revving a manual car and then dumping the clutch but not as harsh.

Go for the 2800. A bone stock 300mm LS1 converter flashes at 2000 RPM.

[Joe 1320]

I've had a 3500 rpm stall converter on the street. It's marginal for street use, great for the track. I've driven a couple of 2800-3000 stall converters in LT-1 cars and for the street, it's pretty aggressive. 2400 is a great street converter, but if you do alot of racing you'll wish you had a little more. So in my opinion, street= 2400 rpm. Street/strip =2800. Strip only= 3200+ depending on your power curve.

In reality though, it all depends on what you'll tolerate. I've run as high as a 4500 rpm converter on the street. It wasn't great in traffic, but did it ever launch.

[fastTa]

I was just playing around on All Data and it appears that PWM was introduced on the early 95 f-fods.

Another thing to note is that you can easily identify if your car is PWM equipped by looking at the transmission front pump cover. If you have a PWM equipped car, there will be the letters "PWM" cast into the front pump cover.