What exactly does a torque converter do?

[Coop]

I know where it's located infront of the tranny. I know it has something to do as acting like a clutch in a manual truck/car. But my questions are:

What exactly does it do, how does it work?
What is the "stall speed"
What is the best kind of converter?

I have heard that a new converter is one of the best bang for buck mods. I have a '99 tahoe 2door, vortec 350, 4l60e. What would be the best one/stall speed for a daily driver?

Thanks in advance for the help!

[xlong4x4]

howstuffworks.com has a detailed description of how an auto tranny works including a section on torque converters. It can't answer your upgrade question, but it'll help you understand what you're looking for.

http://auto.howstuffworks.com/automa...ansmission.htm

[FoxTrot]

Originally posted by Coop
I know where it's located infront of the tranny. I know it has something to do as acting like a clutch in a manual truck/car. But my questions are:

What exactly does it do, how does it work?
What is the "stall speed"
What is the best kind of converter?

I have heard that a new converter is one of the best bang for buck mods. I have a '99 tahoe 2door, vortec 350, 4l60e. What would be the best one/stall speed for a daily driver?

Thanks in advance for the help!

Same question here. Think dealerships would give a person crap about their warranty if they had one?

[Cop_Dodger]

A torque converter acts as a fluid coupling for the automatic transmission. It has fins in it that act like fans. This is how it works. Take two fans and face them towards one another. turn one of the fans on. If the fan speed is fast enough the other fan will turn. The amount of speed the driving fan needs to turn the other fan is what you call the stall.

The advantage of a torque converter is it's ability to multiply torque at lower RPMs. This is why automatics are better then manual transmissions in some applications.

[FoxTrot]

What determines what stall you want?

What would be best for a daily driven truck like coop asked?

[HaulnA$$]

What determines what stall you want?

What would be best for a daily driven truck like coop asked?

The main factor in determining converter stall speed is the power band of the camshaft. You dont want the convertrer to kick in at 1600 RPM if the camshaft doesn't wake the engine up til 3000 RPM, something will eventually go boom. On the other hand, if the stall speed is too high for the cam, it'll fall flat on its face. Your friendly camshaft manufacturer can recomend the proper converter to match their cam.

[Coop]

Well, I have the factory cam in my vortec 350? What stall speed would help wake the truck up?

[cravnpup]

The vortecs torque peak happens at 2800rpm, but for a daily driver you may not want to go too high.. I'd say between 2400 and 2600 stall speed would be about right...

[Hit Man X]

Originally posted by Coop
Well, I have the factory cam in my vortec 350? What stall speed would help wake the truck up?

I've got a nice write up I did for converters. When someone replies I'll post it up as it is on my home computer.

But a large diameter like an 11" converter with a 2600-3000rpm stall with a 2.2-2.6 STR is going to be a nice street converter. I can go on and on about them...I'll just post up my write up this evening.

[Coop]

what is the factory stall speed on the factory converter?

look forward to that writeup, thanks hitman

[Hit Man X]

Converters are the "black holes" and "voodoo" of cars and trucks. They are strange, complicated, and misunderstood.

First, stall is based on input torque. I.e. an anemic, low compression 350 may be able to stall a converter to about 2000 rpm. A hot, higher compression with good heads 350 may be able to get that stall up to 2600 rpm due to making more torque. That is with the same converter. It really depends on your motor.

Stall also is in different forms. There is flash stall, brake stall, and actual stall.

Flash stall is, with no traction problems, the peak RPM or the quick jump of the engine RPM's on with the converter. This isn't the best way to measure stall. Insane amounts of torque can make a 3000rpm stall to 4200rpm+
Brake stall is, holding down your brake and gassing the ride with the other foot. That doesn't work too well either b/c you will generally begin to light up the rear tires.
Actual stall is if you had a line lock on your trans (holds R+D together) so you don't move and your RPM's rise to your stall speed. If you have a 3000rpm stall, that is what your engine should rev to with the line lock on. You would launch off of that.

Softness depends on the stall and size you go with. High stall, small converters are "loose" converters if you will. Larger diameter usually help keep the looseness away and keep the factory towing up. These act more stock with higher stall. The softness is more likely to be with the part-throttle shift than the WOT ones.

Looseness is hard to explain. Like you'd have to give the vehicle a bit more gas to get moving and depending on diameter. Generally your part throttle putting around rpms are about 2000-2200rpm.

Precision Industries recommends a TransGo shift kit (at least they used to, prolly still do) to be installed with the converter. Check out all the car mags like: 5.0 Mustang, CarCraft, Hot Rod, GM HighTech, etc they all install shift kits with the converter install.

A high quality TransGo kit addresses trans problems and corrects them. 3-4 burn up, 2-4 band loss, etc. They boost line pressure but also keep more fluid on the clutch packs, and get rid of the slop shifts.

I recommend at least the Corvette servo but prefer the Superior billet servos. On the passenger side of the trans is the 2-4 band apply servo and the overdrive servo. I think it is silly to not install both of the bigger servos at the same time you install a shift kit as you have to clearance the band. The servos increase holding capacity (the OD billet is 10% greater over stock. Intermidiate billet is 35% more apply over 'Vette servo, so I'd figure about 50% greater than the non-'Vette servo)

Finally, with a high stall converter, install a large transmission cooler. Even if the instructions say it is okay to use the factory cooler/heat exchanger get one. They are cheap insurance. $50 cooler or $2000 transmission?

[Coop]

allright, looks like I am going to just leave mine alone

[Hit Man X]

Originally posted by Coop
allright, looks like I am going to just leave mine alone

A converter will make a HUGE difference in how your truck performs under light loads. I hope that didn't overwhelm you or anyone else. That's just the easiest way to explain them.

Even a mild stall of 2400rpms would make a nice difference on a stock truck...my F-150 has a 2200rpm in it.

[Coop]

but if you have to go in and change all that other stuff, doesn't it make it a huge job? I know dropping the tranny is big enough.

[Hit Man X]

If I were to do only three things to a vehicle with an automatic I'd do:

Stall w/ shift kit
Long Tube Headers
Tune

The stall and shift kit will make the truck FAR more responsive from a dead stop. You'll hop right up into the powerband. I'd try to go for a ride/drive a vehicle with stall. It's a wonderful thing.

The TransGo isn't absolutely necessary but really makes the trans shift great. Plus it keeps it alive longer.

[Coop]

so what brand/stall/size should I go with for a vortec 350 w/intake/electric fan/exhaust? Thanks for all the advice so far.

[Hit Man X]

Originally posted by Coop
so what brand/stall/size should I go with for a vortec 350 w/intake/electric fan/exhaust? Thanks for all the advice so far.

First do you tow and what's your budget for the converter?

[Coop]

don't tow, budget maybe no more than $400, truck is 2wd going to be lowered, going for a sport truck, faster the better.

Also, what does it feel like to drive a higher stall converter? when you are pulling off the line, just slowly, does it sort of rev up and then go, or does it still act like normal, starts going when you press the gas?

[Hit Man X]

Originally posted by Coop
don't tow, budget maybe no more than $400, truck is 2wd going to be lowered, going for a sport truck, faster the better.

Also, what does it feel like to drive a higher stall converter? when you are pulling off the line, just slowly, does it sort of rev up and then go, or does it still act like normal, starts going when you press the gas?

Hrm, I'd call Yank www.converter.cc and see what they can do for you. Your 4L60E should have a 30 spline input shaft and they make converters for 33 and 30 spline input shafts.

They sell a 2400rpm stall for $400 I believe. But the current Trailblazer converter is a 2600rpm stall for ~$300 new from the dealer.

The feeling of stall is totally dependent on the converter chosen. It can be loose as a goose or tight like stock. Typically lower stall and larger diameter are like stock

[2k1Sierra]

The new Trailblazer has a 2600 stall which is around 300 more or less...I wonder what cost is
That would be a nice improvement over stock.
I'm pretty sure it would fit right in the 99+NBS trucks 4L60E, I just don't know about any affects the weight difference would cause.
Hit Man...any thoughts?