torque converter what stall speed

[Monca68]

Im putting in a rebuilt 302 with a little bigger of a cam. 4:11 gears eventually 4:56s 35" tires and a C 4. Where do I want to be Im guessing around 1400?
Thanks for any info

 

[garberz]

That;s a bit low. I'd stay with the stock stall speed which is 1800 rpm, + or - 50.

 

[Broncobowsher]

The lowest you can get away with for the cam you are running.

 

[Monca68]

The guy at the trans shop suggested 1800 for some reason I thought that would be too high.You said the stock stall speed is 1800.what would be the lowest if I were to go lower and what the difference be I assume the gas mileage would be better. What are csome of you guys using?

 

[englewoodcowboy]

Call the cam mfg. They will ask you some Q's about your use etc and will tell you what stall you should get.

 

[broncnaz]

Picking the correct Torque converter can be very tricky is mostly based upon engine torque and camshaft but vehicle type, gearing and tire size all factor in. You probably wont see any real mileage gains going to a lower stall converter with a 302 in a bronco. Ther 302 is not the best low speed torque making engine especaill in in a bronco with big tires. But then again you might be able to pick up a little mileage wouldnt expect anything major. You really should call a few companies and ask them just have all your specs ready camshaft specs and tire size and gearing will probably be the most important

 

[Monca68]

I wish I would have thought about this sooner. I was planning on putting the tranny in tomorrow. I dont want to be sorry and rush this like I do everything else but I want to start driving it again.

 

[Broncobowsher]

Be forwarned that most performance shops will think street or race performance for the converter stall speed rating. Something to make it livelier off the line. Something that lets the motor really come up into the powerband hard off the line. Fun on the street but not so good on the trail. Therefor get the low side of the recomended converters.

I had Roadrunner Converters work over a stock converter that was a little too tight for the cam I was running in my ranger. They clearanced it as much as possible so it wouldn't pull the motor down when you dropped it into gear, but the overall stall and performance was nearly the same. If you have a good local convertor shop around that can do custom work that might be a good choice.

 

[Monca68]

So if the stock converter is 1800 and I put that in would I be sorry?

 

[englewoodcowboy]

What kind of cam did you go with? I chose a rv type cam and was told to get a converter in the 1800-2000 range.

 

[broncnaz]

Unless you have a big cam like something with around/over 220 duration @.050 the stock converter will be fine. Most of the cams we tend to run in broncos dont require converters. Since your putting in the C4 tomorrow I would go with what you have. rushing to buy something now will probably lead you to buying the wrong thing.

 

[HGM]

So, in case anyone is in doubt. The stall speed is where the power of the engine is transfered more directly to the transmission, less slip. Therfore, if you have a drag car and your engine Tq comes on at 3kRPM, you'll want a converter to come on up near that range. For us 4x4 guys, BB is absoloutely correct. You want a converter to come on as low as possible. Meaning that, most of us will have a low end Tq cam, making its power in the 12-1500 RPM range. If you have a converter that stalls up near 3000, you'll have to rev close to that 3000 to begin moving. Immagine climbing a rock at 3000RPM in a manual trans and releasing the clutch.. The more low end Tq your engine has, the lower converter stall should be. Again, visualize a tractor or diesel with a cluch. You can release the clutch w/o throttle input, much less likely to stall than with a higher strung, higher reving Mustang.

Dont know if that helps, but if you're putting a similarly powered engine in with the stock converter, you'll be fine.. Would definitly feel better with a lower stall off road. Even a higher stall on the street would feel better if your cam is making the power up there.. So, depends on how your driving... 1800 might just suit your needs better..

 

[Broncobowsher]

So, in case anyone is in doubt. The stall speed is where the power of the engine is transfered more directly to the transmission, less slip. Therfore, if you have a drag car and your engine Tq comes on at 3kRPM, you'll want a converter to come on up near that range. For us 4x4 guys, BB is absoloutely correct. You want a converter to come on as low as possible. Meaning that, most of us will have a low end Tq cam, making its power in the 12-1500 RPM range. If you have a converter that stalls up near 3000, you'll have to rev close to that 3000 to begin moving. Immagine climbing a rock at 3000RPM in a manual trans and releasing the clutch.. The more low end Tq your engine has, the lower converter stall should be. Again, visualize a tractor or diesel with a cluch. You can release the clutch w/o throttle input, much less likely to stall than with a higher strung, higher reving Mustang.

Dont know if that helps, but if you're putting a similarly powered engine in with the stock converter, you'll be fine.. Would definitly feel better with a lower stall off road. Even a higher stall on the street would feel better if your cam is making the power up there.. So, depends on how your driving... 1800 might just suit your needs better..

Misconception about high stall converters. You should be able to move at idle speed. But with minimal driving force. Driving force will rise as RPM increases up to the stall point (in this case 3000 RPM). At 1000 RPM you should have driving force but so little you could just about hold the vehicle back by hand. At 1500 RPM you would have the driving force roughly of what a stock convertor would put out at idle.


Years ago I had a friend with a big bad drag car. Loading it on the trailer with the 3800 stall converter wasn't that bad. It did take 2000-2500 RPM to get up the ramps. Running around the pits at 1000 RPM idle was just like idling around in a normal car only it made a lot more noise. It would have been completly useless for a trail vehicle. But it was entertaining breaking the tires loose on the street doing 90!

 

[RRRAAAYYY2]

Call Len at Lentech, or Hutch on this forum: http://www.yellowbullet.com/forum/forumdisplay.php?f=30

Two of the best in the world, so I sure they can give you great advice.

 

[HGM]

Misconception about high stall converters. You should be able to move at idle speed. But with minimal driving force. Driving force will rise as RPM increases up to the stall point (in this case 3000 RPM). At 1000 RPM you should have driving force but so little you could just about hold the vehicle back by hand. At 1500 RPM you would have the driving force roughly of what a stock convertor would put out at idle.


Years ago I had a friend with a big bad drag car. Loading it on the trailer with the 3800 stall converter wasn't that bad. It did take 2000-2500 RPM to get up the ramps. Running around the pits at 1000 RPM idle was just like idling around in a normal car only it made a lot more noise. It would have been completly useless for a trail vehicle. But it was entertaining breaking the tires loose on the street doing 90!

True, you clarified what I had in my mind...;D I was trying to lay out the "climbing a rock" theory. Guess the sentances were reversed..

Anyhow. It may also help to envision a fan being directed at another fan. One being powered, the other not. The pitch of the blades will dictate the air movement and will make the other fan move in relation to fan speed. Changing the pitch of the fan blades will change the fan speed required to move the non powered fan. If that makes sense.. Will it move at low speed, yes, but there is an optimum RPM for force transfer, based on pitch..

 

[Broncobowsher]

True, you clarified what I had in my mind...;D I was trying to lay out the "climbing a rock" theory. Guess the sentances were reversed..

Anyhow. It may also help to envision a fan being directed at another fan. One being powered, the other not. The pitch of the blades will dictate the air movement and will make the other fan move in relation to fan speed. Changing the pitch of the fan blades will change the fan speed required to move the non powered fan. If that makes sense.. Will it move at low speed, yes, but there is an optimum RPM for force transfer, based on pitch..

We are starting to stray from the original question a little bit, but still relivent...
The 2-fans is a really simple laymans way of describing the fluid coupling effect. But that is more based on a linaer axial flow. A converter will be a toruidal flow. To half simplify a bit a radial flow pump (water pump, centrifical compressor wheel). The tip velocity is the primary factor in the convertors speed. Much like a tire diameter changes the velocity to RPM relationship. A small diameter convertor (say an 8" race convertor) will turn a much higher RPM for the outer diameter velocity. The lower the RPM the larger the diameter. But the surface speed of all the convertors is very comparable regardless of application.
Now there is the clearance between the 2-fans which is the clearance between the impeller, stator and turbine blades. Really close and it will be a tight convertor. Lots of driving force at low RPMs where you open the gap and the fans spill a lot of the driving fluid at low speeds, this keeps engines from bogging down when placed in gear. There is a minimal effect to stall speed by this but will allow big cammed engines to idle better in gear at the loss of low speed (idle) power transfer.
Then there is the whole blade shape thing as well. This will greatly affect the multiplication ratio and is the second biggest influence in the convertors performance (only the diameter is a bigger affect). For the 4R70W I was at Hughes and they were showing me 3 different 4R70W/AODE convertors and they could tell by the fin angle showing through on the case how each of the 3 would behave different. I wish I remembered the details a little more, I just remember that the Explorer 5.0 convertor I had was the one we determined to be the best.

So there is a LOT of variables that can go into a convertor that will affect the overall performance a lot more then just "stall rating". Spend some time around a place that actually builds custom convertors and you will learn a LOT.

Back to the original question. A stock convertor will probably be fine. Sounds like what you have picked out should be fine. You really should plan the entire drivetrain as a package. Running a bigger cam generally requires a little looser convertor so it will idle (your 1800 stock replacment soulds like it will work based on what you have provided us). but you may need some gearing changes as well. Your highway cruising speed should be higher then the rated speed of the convertor. This will keep the convertor more into the efficient coupling stage and less in heat building multiplying stage. Convertors running in the multiplication range of there powerband will multiply torque coming in (actually exchanging RPM for torque so power in = power out) but it isn't a perfect conversion and the result is heat. Excess heat is bad for transmissions and you have to waste fuel to provide that heat.

 

[Monca68]

If Garberz is sure that the stall speed is 1800 I think I might just use that . Does anyone else know for sure I just dont want to do this twice. Thanks Rick

 

[spadus]

I built a 347 stroker and my engine tech installed a 2,400 stall. I'm getting ready to rebuild my C-4 and my tranny tech mentioned he is going to put in a new 1,800 stall or less. I crawl in the mountains and I race on the street and it seems to work great in both instances. If I had to make an observation, I believe the lower stall setting would work better for me due to the slow trail driving. The higher stall seems a little sluggish on the trail. In addition to your engine specs, make sure you realistically describe how you're going to use your rig the most.

 

[garberz]

If Garberz is sure that the stall speed is 1800 I think I might just use that . Does anyone else know for sure I just dont want to do this twice. Thanks Rick

Here's an older thread about stall speed. Looks like Viperwolf1 can back me up on this. Post #6.

http://classicbroncos.com/forums/showthread.php?t=157521&highlight=stall+speed+C4