Explain torque converters please

[tpodwdog]

howwwwwwwwwwwwwwww-deeeeeeeeeeeeeeeeeeee....the Dawg here again.

i put a tach in the Belvy today because i felt i needed one. the car is a 440 beefed up with a 3500 torque converter. it sure does rev high just to get it going....but just juice the gas a bit and sheez layin a good long strip.

from my understanding of torque converters is this :

a 3500 converter will totally lock up at 3500 rpm.....right ? so the rest of the time its not locked up and kinda "free wheeling ???"

i put the tach in coz i wanted to see just high it was revving on a pullout....cruise...and layin a strip. can anyone tell me if this 3500 TQ CONV is a good thing to have coz i DONT race it....just joy ride and an occasional " light 'em up " i have been told that with that kind of horsepower, id be better off with a 2800 coz it will eventually burn up thanx!:headbang:

 

[ArtH]

http://www.badasscars.com/index.cfm/page/ptype=product/product_id=78/prd78.htm

 

[daredevil]

what gears do you have in the rear?

 

[egrand1508]

http://www.youtube.com/watch?feature=player_detailpage&v=x-OFiTUne_M

 

[70rr-brian]

You pretty much hit the nail on the head. I have a 4k stall in mine with 3.55 gears...Yeah I know...I am going to bump up the gears to 4.xx this coming summer. The main reason is if I get it stuck with a slow rolling start in 2nd gear I basically have 2 choices to get it moving...wait for the 2nd gear to get enough r's to start accelerating at something faster than a snails pace or kick it down into 1st and lay rubber and slide sideways down the road. Of course if I had a manual valve body with a console shift this problem wouldn't be a problem. But since I left the original column shifter in it and don't use a manual valve body I am at the mercy of the kickdown linkage. (cause I am NOT manually shifting the column shifter...sloppy as hell and too easy to go too far)

The main thing with high stall, well any stall, but more noticable with higher stalls is the amount of RPM's necessary for it to fully engage the converter. The term Flash is often used to define how many R's need to be hit before you see any considerable movement. (Ever brake torque a car? The tires will generally start spinning when the converter fully engages....or there abouts) If I want to go anywhere, even slow, the motor has to flash to 4k before I start getting any serious movement. I am sure you probably have noticed that you are probably flashing around 3500 to get some movement. Anyway, once you get past you number, whatever it is....the TC is no longer holding back the engine power from the rest of the drivetrain. So for you...if you arent doing full throttle runs all the time and say driving it on the highway...you would need to have built up enough R's to get past the hold back point of the converter or enough speed to get the R's or essentially the TC is always engaged. Being engaged all the time is not good. (Say you mostly drove highway and held 2800r's) Generates heat and heat is a killer. So run a good trans cooler or bump up the rear gears to get the r's to suit the cars normal use patterns to get past the stall range.

Hopefully that made some sense...Didn't look at the videos but I am sure they probably explain it better than I did.

 

[RustyRatRod]

A MODERN converter can have the ability to be both street and strip friendly. USED to be, they reacted similar to what you describe. There's really no set in stone RPM where a converter locks up. They never lock up 100% unless they have a magnetic clutch as in a lockup converter. Lets say for kicks and giggles we have a converter in a car that does flash to 3500. Put it in another car with more motor, more weight and less gear and it will flash to 4500. Why? Because more motor=more torque. More weight=more intetia to overcome. Less gear=less leverage, so all that means the same converter will flash higher. Converters are torque multipliers.......they are kinda like small transmissions. They see X amount of torque as an input and give more than that as an output. That's why I like automatics in a race car. They cannot be beat. A clutch cannot multiply torque. What it sees on one side it sees on the other....and possibly less in a racing situation because clutches can slip. There are a lotta variables with converters. That's why I never tell anybody to buy one off the shelf. Custom is the only way to go.....unless you just gotta slightly warmed over street car and don't give a damn about an inefficient converter that generates a lotta heat.

 

[65affair]

What trans are you running? I would be surprised if you have a lock up converter, unless you running a 46rh trans. so your typical 727 trans with a 3500 stall will always slip. in fact every converter will slip unless its a lock up converter in a transmission that will handle a lock up converter. so, my two cents would be that your over converted. I am not sure of your build, but most street cars shouldn't have that high of a stall. your converter is always slipping (more than normal), so, your trans is building more heat than necessary. if your were racing this car with limited street use then that converter might be fine with the proper build.

 

[Meep-Meep]

A converter in the simplest terms is a fan blowing air (or fluid) to another fan. It also has a built in ratio of about 2:1, which is why an automatic tranny of the era only has three speeds (or even two in some cases) and a manual has three or four. The converter multiplies torque right from the start and that is what replaces the low gear in a manual tranny.

A higher stall speed is required when the engine is tuned to produce more power at a higher RPM, or more specifically start producing more power at a higher RPM. Everything must be matched. RPM curve, converter, gearing, car weight, etc.. A high stall converter (say 3500 RPM) with tall gears that allow a cruise RPM of 3000 at 65 MPH is just generating heat because the converter isn't "locked up" at those speeds. A high stall converter should be matched to low gears and an engine that has upper RPM torque.

 

[tpodwdog]

gears are 3:55 sure grip......tranny is a torqueflite (normal shift...no crazy valve bodies ). it will move well before 3500 RPM. ...but it dont act like my Road Runner ( which is all stock). the car runs and shifts fine (although im in 3rd gear really fast if i dont get on it too much )....there are no problems with the car...it just seems as compared to the RR...i gotta give it a bit more gas to get it moving.....but it will spin em off like nobodys business with just a small amount of gas....even in 2nd gear when the car is on the move.

if i drop it in drive.....it wont do the normal "automatic drift"...it will just sit there until i give it gas....but you can feel it engage. it cruises at 60 MPH at 3000 RPM. there are no issues, i just wanted to know if all this was normal from a high stall converter because i really dont know much about automatic transmissions.

so, the tranny burning up wont be an issue as long as i have the tranny cooler in place ? i put in a new radiator the other day and took off the tranny cooler that was on there coz it was an eyesore, and am now using the internal cooler in the radiator..( i figured that would be ok since i dont race the car ). but i have every intention on getting a new tranny cooler and getting it on there ASAP as per your recommendations.

thanx alot guys...appreciate the time you gave to this question!

 

[70rr-brian]

gears are 3:55 sure grip......tranny is a torqueflite (normal shift...no crazy valve bodies ). it will move well before 3500 RPM. ...but it dont act like my Road Runner ( which is all stock). the car runs and shifts fine (although im in 3rd gear really fast if i dont get on it too much )....there are no problems with the car...it just seems as compared to the RR...i gotta give it a bit more gas to get it moving.....but it will spin em off like nobodys business with just a small amount of gas....even in 2nd gear when the car is on the move.

if i drop it in drive.....it wont do the normal "automatic drift"...it will just sit there until i give it gas....but you can feel it engage. it cruises at 60 MPH at 3000 RPM. there are no issues, i just wanted to know if all this was normal from a high stall converter because i really dont know much about automatic transmissions.

so, the tranny burning up wont be an issue as long as i have the tranny cooler in place ? i put in a new radiator the other day and took off the tranny cooler that was on there coz it was an eyesore, and am now using the internal cooler in the radiator..( i figured that would be ok since i dont race the car ). but i have every intention on getting a new tranny cooler and getting it on there ASAP as per your recommendations.

thanx alot guys...appreciate the time you gave to this question!

My personal feeling is that you should probably have a seperate tranny cooler under the circumstances if your car sees prolonged street driving. Ironically, racing the car would probably be less harmful from a heat perspective than driving it around with a TC that is always holding back. My other recommendation would be a 4.xx gear or just lower the stall. TC recommendations are usually made based on cam specs, (lift, duration, etc...), car type (weight) and gears. They make assumptions with those numbers about where peak engine power will come in. I'm just curious if you consulted a TC company or good tranny shop for their recommendations with your particular setup/specs and if so was that their recommendation?

Here's a nice article: http://www.hardtail.com/techtips/selectingconverter.html

 

[tpodwdog]

well....i havent checked anything , but this is what the previous owner told me about the engine:

10.5 compression
Hemi cam in a 440
has a holley 750 DP vac secondaries (installed by me)
had a larger tranny cooler (removed by me when i added the new rad)

i am going out today to get new lines and a tranny cooler and it will be installed today !

what you said about racing it makes sense about it running cooler. i still have the tranny cooler. would you suggest 2 tranny coolers coz i did buy a new one...but when i opened the box, it was about half the size of the original.

 

[bigmanjbmopar]

I have the stock converter in my 727 with my 493 in front of it, and she rips it from standing stop all the way till I pee my self with no brakes needed (3:55 surgrip). Stock stall is around 1100 rpm I believe? I don't think you need 3500 stall unless your a track car I mean what's the point of stall that tall?

 

[BuckNeccid]

Where does your engine make power? If your power starts coming in at about 2500 rpm, then you're wasting 1000 rpm by having a 3500 rpm stall. Try to balance everything. I'm running a Lunati roller with the power ranging from 1800-5500 rpm, and I'm using a 2800 stall convertor. There's been a lot of good info up here, but if you're using the car for street driving, most of your rpm range that's going to be used is off idle to maybe 4500 rpm. You want a fast leave and burn outs? The Hemi cam is gonna give good power at about 2800-3000 if it's the one I think it is, but you're also gonna be cruising 55-60mph at about 3000 rpm. If you're stalling 3500 rpm, then you're gonna have a lot of slippage at highway speeds. If you want burn outs, then you should still have plenty of power to do them stalling to about 2500, but reduced slippage and better gas mileage, longer life and less heat with that stall. I think you have too much convertor there, and just changing the rear gear isn't gonna be the cure all. When you're leaving a red light, the convertor still should be pulling as soon as you put it in gear, just with slippage. The stall idea is sorta like a clutch idea, you rev it to where you want, then dump the clutch. A stall "Flash" is supposed to work, but when you want it to, you hit the gas hard, the engine should quickly rev to the stall point, and then connect and move the car. The faster the engine revs, the more torque it has, and the higher the stall point will become. Just because something says 3500 stall doesn't mean it will stall to 3500, it just means it's gonna be somewhere in that range, IF your engine is built close to the engine they based the 3500 stall rating on. If you read up on this, almost everything you find will tell you to build everything to match. There's no way we can give you everything you need to know about this on a forum, but you've sure picked up a LOT of good info here.

 

[daredevil]

what buck said. And stay 500 to 1k less than cruising rpm at 60 and you should be happy.

 

[tpodwdog]

ok,,,,thanx for th info,,,and with all that explained....how do i actually KNOW what converter i have? if i power brake it...and the wheels start spinning at 3500....then i have a 3500 converter,,,,,right?...if they start spinning at 2800...i have a 2800 converter and so on and so on ????

 

[70rr-brian]

"The old definition of stall speed used to be the engine RPM at which the brakes
can no longer hold the wheels still at full throttle. This is not exactly
accurate, due to the variations in brake holding power from vehicle to vehicle.
In other words, in two cars that are exactly the same weight, horsepower, etc.,
the one with weaker brakes will display a lower stall speed, even if it really
isn't, because the brakes will lose their grip at a lower RPM. The most accurate
method for determining actual stall speed on your vehicle is to launch the
vehicle at full throttle, and note the rpm at which the car actually takes off
(this generally requires a partner watching the tach). This will be quite low on
stock vehicles - around 1500-1800 RPM, slightly higher if the engine has been
modified. "

 

[tpodwdog]

****UPDATE UPDATE****

just put the tranny cooler back on. i used the new one coz it has the same surface area (actually more) than the old one...its just a different shape. the tranny fluid is at the right level but its a bit darker red than normal....i guess it needs changed and ill get to that very soon.

thanx yinz guyz for all the help thru this. this is the best MOPAR site goin!

 

[bigmanjbmopar]

I'm just jealous you have two cars now man.....wanna trade wife and kids for the 70?


:evil5:

 

[HT413]

High stall converters generate serious heat when you cruise below the stall rpm - especially the garbage brands. I'd put a temp gauge on it and if the temp gauge goes into the danger zone just by using the car the way you want to... then you know you need to change the converter.

 

[tpodwdog]

no BIGMAN....i got rid of a woman so i could HAVE 2 cars ! lmao....and im allergic to kids!

- - - Updated - - -

HT413....i was thinking that exact thought...thanx!!