NewbVetteGuy

I'm hoping someone can teach me quickly the things that I need to know to make an informed decision about Torque Converter stall speed implications.


One of the questions that's very high up my list is understanding how much going with a higher TC impacts fuel economy and when.

-Is the issue ultimately just that the higher the stall rating of a TC the more it "slips" when not locked-up and this slippage is essentially engine power that doesn't get turned into wheel power? If so my understanding is that a higher stall essentially results in reduced fuel economy any time the TC isn't "locked" -is that right?


When do lockup TCs normally "lockup" -it's only in high gear, at a cruise at low throttle angles, right? Is there any other time?


I understand that the TC needs to be matched to your total vehicle combination including weight, and CAM at the top of the list with general Torque curve considerations.


-I've been mostly looking at middle-of-the-road cams that balance performance and low-end-torque/fuel economy (my C3 will weigh roughly 3400 lbs) - most of the cams I'm looking at say to use a "stock" TC, BUT I'm really starting to think hard about putting a FIRST https://www.firstfuelinjection.com/ beast of an aftermarket tuned port-style intake on this thing and doing port injection; Grumpy's site recommends high compression and a high stall converter with one of these; I'm looking at 10.2:1 so good there....


What's the implication of going with "too low" of a TC stall?
Is it just that my initial acceleration is lower / slightly lethargic? -If so, I'm not sure I care, depending upon what the impact on fuel economy is... -I've got a 4L60e that's going in it which has a super low 1st gear that I think helps; I've also got a 355 rear gear ratio; I also don't mind advancing the cam timing to move the power curve lower to make up for it.


Recommendations please? I've been trying to turn some "unknowns" into "knowns" on this build so that I can move forward and finally buy the trans and Torque converter, this recent idea of getting a FIRST intake and using a Holley Terminator EFI to go straight to sequential port injection is throwing a small kink in my plans....


Adam

dugsgms74

Good questions on a interesting topic. I don't know alot about selecting stall speed but I can share the info that I'm aware of.

As far as fuel economy goes...There will be a drop in economy due to more slippage during acceleration but very little during cruise. Slippage is largely dependent on load and during cruise there is very little load and thus very little slippage. Even a non lock-up will come very close to "lock-up" at cruise. Although a mechanical lock-up is ideal and there is some MPG advantage to it, its not huge.

The times that a the OEM lock-up TC are active depends on the year. Early systems locked-up only in higher gears at higer speeds but as computers got faster and were able to process more info the times that lock-up occurred got more complicated as more variables were used to determine when the converter locked-up. But for the most part, yes, they're typically locked-up during light load/cruise conditions.

Too low of a stall speed will be a issue if you have too much cam, too little displacement or not enough gear relative to converter selection. Kind of hard to explain but if you've ever ridden a 2 stroke motorcycle and tried to accelerate before the engine comes "on pipe" that would be a huge exaggeration of the feeling you'd experience. Basically you give it throttle at too low of a rpm but not much happens because the engine isn't making enough torque at that particular rpm to accelerate the car. If you had a looser TC in the same situation the extra slippage would allow the engine to operate at a high enough RPM to be in "power band" and accelerate the car.

Stu's81

If your car is strictly a street car, I would go no more than 500rpm higher than what starting rpm is where your cam makes power. example cam range 2000-6000. 2500-2800 stall. I just bought one for a 4l80E I am rebuilding for my car the guy from the converter company took all my cars info and usage and I ended up with a 2800 stall
converter. this is their website. https://www.alltorqueperformance.com/home.html

gkull

You want a 9.5 for less rotating mass and something over 3000. efficiency is the key, not wasted slipping.

http://www.converter.com/vigilante.htm

REELAV8R

Not quite. Since during normal acceleration or slow cruise the load on the torque converter will be less then it will be slipping less. The stall of the torque converter will be reached when it is highly loaded and you achieve that stall speed RPM then the slippage is at a minimum for that converters stall.
I ran a 2600 stall converter and it was pretty normal feeling unless I was pulling a hill at less than stall speed or during initial hard acceleration.

The higher stall converter allows for a few things to happen.
One is it makes it easier for the engine to idle in gear with a higher overlap cam. Higher overlap cams produce low torque at idle and lower RPMs.
Two, it allows the engine to get into it's "power band" or efficient higher torque operating range immediately to produce better acceleration from a stop or low speed/RPM's.
Three, it can be used to keep the RPM's in the efficient RPM range for gear shifts, IE in a drag race scenario. With a stall too low for drag racers the RPM's are allowed to drop out of the power band and this makes for slower acceleration after a gear shift.


Poor idle or unable to idle in gear without jacking the out of gear idle RPM way up.
Poor acceleration due to the engine being below it's power band as determined by the cam in use.
having to "band aid" the cam by advancing it or getting too low of duration to make sufficient low end torque and thereby loosing high RPM capability which you may want for RPM drop between gear shifts. IE you may want to achieve 6000 RPM prior to a shift due to the gear ratio of the transmission/rear diff and the subsequent RPM drop between gears. If the cam is too short to get sufficient torque then you run out of RPM capability to do this.

bluedawg

What cam shaft are you running? I agree with George, I'm running a 9.5 inch 3000 rpm and love it. The main thing about a converter is to match it to your cam shaft, to come on were the power is really starting to be made, this makes the car react to the power band. To small of cam and it will be lazy on the low end even want to die when you put it in gear.

diehrd

My opinion only ... Most street SBC engines will be happy with 2800 to 3000. That rpm is based on average torque of these street set ups and is close enough to give you performance and drive ability


Look at Torque not hp when you choose a converter. If a cam shows a power band of 2000 to 6000 find where the max torque is and base your stall off that. If you are not trying to make it the fastest it can be in a 1/4 mile take that torque number and cut up to 30% off it for the stall speed.


.. And the other important issue is rpm drop between gears. A higher stall keeps that loss smaller then a low stall converter does which means your engine is able to stay in its power band before and after a shift , we all can relate to this in most any car . You floor it , it shifts and the engine has to build power through the gear change. Higher stall drops less rpm keeping the engine in a sweet spot that keeps the helliacious pulling going lol ..

There are math formulas to use if you are a dedicated go fast guy and of course the track and a good converter company can all help in finding that sweet spot.

NewbVetteGuy

Reminder on goals: I'm looking for a good balance of fuel economy and performance with plenty of torque down low and in the mid range, so my cam might be smaller than most of what you would go with. I'm looking at a retrofit hydraulic roller cam.

The cam that I've been recommended looks like:
264/267 @ 0.006"
216/220 @ 0.050"
.340"/.340" lobe lift
.510" / .510" valve lift
110 LSA
107 ICL

I've also been looking at a 212/218 @ 0.050" cams with the same lift and LSA.
The RPM rating for that cam is 1,200-5,200. So I should have torque pretty low in the band. This is also a "fast ramp" cam- I'm actually not so sure I've made up my mind on going with a fast ramp or a slower ramp cam, to be honest. --I don't want to have to run high spring pressure and have possibly longevity issues with the fast ramp cam and I don't like that the valves are likely to float earlier, although with the cam's rating stopping @ 5,200, maybe I really don't need to worry about it.


I'm also considering a TPI-style intake (FIRST) but one that's WAAAY less restrictive than an L98 TPI intake; I'm still not totally clear on whether this intake drives my RPM range upword or downward but my feeling is that it gives me even more torque down low. -With my low 1st gear, I'm really thinking that I should be good with a lower stall TC, but I'm just not sure.


Also I'm doing a 4L60e swap and with my 355 rear end I'll be turning 2166RPM @ 70, and 1702RPM @ 55 MPH. -I know I probably need to keep some torque down low given the low RPMs at cruise in OD.

--This is one of the things I'm confused about- if I shift into 4th and the lockup TC hasn't locked up what is the implication of turning fewer RPMs than the TC Stall?


This torque converter thing is so confusing. Do they really only slip more when you're accelerating?



Adam

NewbVetteGuy

One of the things that keeps freaking me out is that the Grumpy's Garage site has a ton of information on TPI intakes and inparticular the FIRST intakes and he recommends a 3,000 rpm stall for people going with that intake. -But his recommendation always comes with a recommendation for a huge cam- I think he's talking about building a total package that takes full advantage of the intake's ability to flow...


If the car accelerates a little bit slower I'm not really concerned, I'm never going to race it, but I definitely need the ability to do great burnouts and smoke the tires when I want to and I AM concerned about being able to get decent fuel economy and cruise happily at 60-70 mph at lower RPMs...

This whole TC thing worries me because I just don't understand the implications of going with too low / too high of a TC stall.

Adam

gerry72

Too high is much easier to live with than too low.

NewbVetteGuy

Thanks guys, I know I'm a bit slow to listen when I don't understand how something works and I am quickly learning that picking out a perfectly matched torque converter is about as complex as picking out the right CAM or perfectly tuning an exhaust; all shockly complex things if you want to take it to the extreme and understand as much as possible.


As always the Grumpy's Performance blog has been hugely beneficial, along with all the posts here. http://garage.grumpysperformance.com...ll-speed.1715/


Things I've learned along the way:
As Gerry said, within reason "too high is easier to live with than too low" -bogging and a bad idle and a car that wants to die when you take off is a bad thing.

Higher TC stall speed DOES result in fuel economy / efficiency losses and increased heat under acceleration, but is a necessary evil.

Torque converter lockup is a complicated thing; the early implementations were simple "on/off" implementations that use cheap lockup torque converters; improved fuel economy and smoother transition from unlocked to locked comes from smarter more modern lockup mechanisms- the later 1st gen 4L60Es (some 1996 & 1997) came with a pulse width modulation (PWM) strategy which allowed the TC lockup to slowly engage and to engage in 3rd or 4th gear to help improve fuel economy and make the transition smoother. -PWM support is nice for fuel economy improvements, especially when using a higher stall TC, BUT it REQUIRES using a lockup TC with carbon clutches ; the PWM tech has gotten a bad rap for reliability because so many aftermarket high stall TCs don't use the carbon clutches that wear much better and last longer and produce less heat- PWM being implemented in the transmission+controller will burn out the clutches on a non-carbon TC. -Lots of tranmission shops and performance enthusiasts started recommending replacing the stock springs in PWM 4L60es with stronger springs to skip PWM support and turn these transmissions into simple on/off TC lockup with the thought that this would prevent longevity issues from using an improper TC (no carbon clutch) but it actually creates longevity issues of it's own by using way too high of pressures on the lower quality clutch plates. Great article from Sonnax: http://www.sonnax.com/articles/241-2...-modifications


More modern transmissions (1998+ 4L60e and many other modern computer controlled transmissions & some random implementations of the 97 4L60es with the 245mm splines) use even more advanced computer controlled logic via a lockup strategy called "EC3" that's a modified PWM strategy that's even more aggressive (improves fuel economy) and never fully provides a true 1:1 lockup- this requires an even higher quality woven carbon clutch material so you don't burn up and overheat the TCC lockup.

If you really want to get rid of PWM-types of TC lockup and don't care about the fuel economy gains you can either buy a non-PWM 4L60e (PWM models literally have "PWM" stamped on the case), or you can use an aftermarket trans controller that lets you set the PWM to simply go from "0" to 90% or 100% applied power during lockup. -This will make it a simple on/off control without the risk of just using aftermarket springs that are too strong and that will burn-up the trans. Sonnax sells a mechanical TCC pressure limiter fix that will also physically prevent the transmission from working in a PWM mode and prevents applying too much lockup pressure like the old-school high pressure springs use.


Personally, I have a trans controller that supports PWM modes of control and I'd like the fuel economy improvement and smoother feel; I like the idea that I can have a higher TC stall for taking off a bit quicker AND the fuel economy improvement of a smarter TC lockup control, but it means carefully searching out the right PWM capable 4L60e (not hard), making sure that the trans shop has kept the PWM circuit functionality intact and hasn't bypassed it, AND -here's the hard part, purchasing an appropriate TC that has woven carbon clutches.... Right now I'm having a hard time finding a list of TCs that have woven carbon clutches or that will even tell you what clutch material they use. I looked at the B&M Hole Shot series of TCs but they don't even list the clutch material...


Adam

7t9l82

FTI built me a custom converter, 2800 stall 9.5 in diameter. The built it so it doesn't slip alot and comes with a free adjustment. They offer a lifetime warranty at extra cost. As gkull was suggesting the smaller diameter reduces reciprocating weight ,that in turn let's the engine Rev quicker.it is noticibly better just normally driving.I never check mileage but it certainly is no worse. Your going to need some sticky tires to make use of it.I have Drag radials and it's lots of fun. There's alot of these modern cars that don't know what hit them.

7T1vette

Yes. Here is what you need to know:

Make a list of your engine build components, estimated horsepower and torque at its peak rpm. Also note the transmission type and its power handling capabilities. Record your rear axle ratio and size of the rear tires.

Now, determine what torque converter companies are possible candidates for you based on your knowledge and info from others, internet assessments, etc.

Finally, call each of those companies, ask to talk to the tech foks as you would like to buy a TC. Then share with them the info on your car and exactly how you intend to use the car (strip, street, cruising, all of the above, etc).

Here's the really important part---->

Let the experts figure out what converter you need based on YOUR information and THEIR engineering experience/data.

If you choose a converter based on what some, all or any of your friends believe, you have very little chance of being successful with your choice. That success rate will be even LOWER if you take the advice of some yahoo at a local car parts store.

There you go!

P.S. You might get good advice on this Forum...but you will also get bumb advice, as well; so that's a real crapshoot.