- This topic has 13 replies, 4 voices, and was last updated 9 years, 11 months ago by
.
-
Topic
-
couple wks. ago i asked about the time it would take to repair my impala’s 4t65e transmission . well i have another question about the torque converter since i will be part way into the trans . the factory unit has a stall speed of 2100 rpm my question is what effect will it have on my trans and engine if i change the converter to a 1900 stall speed unit . will i get better power and fuel mileage in town and highway ??? thanks ..
-
Replies
-
It may affect your fuel economy, but it’s hard to say whether it will be in a good way or bad way.
It will probably cause more problems than it solves. The vehicle was designed with the 2100 for a reason. If you change that, the car will probably think there is a problem and act goofy as crap.Why would you get better mileage in town with a converter thats 200 rpm different ? Performance difference, If you noticed any change at all, it might just end up feeling like a heavier car with no other benefit. Go with the Oem specificaions, whatever they are. Otherwise you might just end up with weird driveability issues and not know why. Generally when people change converters, they go looser, like by thousands of RPMS at one time, and with your application that wouldn’t even be an option. If your car was one specification, and the replacement is something different stall speed wise, say a generic one from Checker auto, this is something the aftermarket company already factored in as giving no change in results from specifications – guessing game, most certainly. This is why its best to know who, on a face to face basis the person who rebuilding your converter rather than buying one. In order get a custom converter built for any gain in performance they have to know all kinds of things about the car, but nobody does this for daily drivers. Rebuilders produce and throw out to the market factory tight or tighter than factory converters like laundry because the looser and smaller the converter is, the more expensive becomes to build, so they builder em bigger, tighter, and cheaper.
It may effect your mileage in a good way. Slippage is lost efficiency and a higher stall speed slips more and create more heat. Also, you may notice the car will creep forward more easily due to the lower coupling speed between the turbine and impeller. You will get better off the line power transfer as long as the engine is within the power band at coupling speed.
Choosing the correct stall speed is based on car weight and engine powerband among other things. The stall speed needs to be higher if the engine makes more power/torque higher in the RPM range and lower if it’s low end.EDIT: As I think about your predicamentmore, you may actually lose off of stop power. This is because it will couple completely too soon and you won’t be in the engine powerband. You want some slippage between the impeller and turbine to get higher in the rpm range for a less torquey motor.
4t65 locks up at speed – no slip- thing isnt going to notice 200 even it didn’t.. When dealing with a low power application like that one, there is no gain one way or the other changing 200 will do nothing. More creep, maybe but its been my experience is that the tighter the converter, the bigger pain it is. I have an electrically activiated on my 442, and its stock speed is something like 1800 which is terrible, but its over 3000 when it gets a 12v hot upon a throttle switch, and then it actually does something. For a performance car on the street a good converter is just south of 4000 unless the car weighs 2000 lbs. Overtight converters in a heavy car is a nightmare for throttle response, plain and simple. I had a fox with an AOD and a stock converter, and some mods, and I could have got up and walked faster than that thing took to get to speed.
[quote=”andrewbutton442″ post=130861]4t65 locks up at speed – no slip- thing isnt going to notice 200 even it didn’t.. When dealing with a low power application like that one, there is no gain one way or the other changing 200 will do nothing. More creep, maybe but its been my experience is that the tighter the converter, the bigger pain it is. I have an electrically activiated on my 442, and its stock speed is something like 1800 which is terrible, but its over 3000 when it gets a 12v hot upon a throttle switch, and then it actually does something. For a performance car on the street a good converter is just south of 4000 unless the car weighs 2000 lbs. Overtight converters in a heavy car is a nightmare for throttle response, plain and simple. I had a fox with an AOD and a stock converter, and some mods, and I could have got up and walked faster than that thing took to get to speed.[/quote] Offroad, we like low stall converters, racing we like high stall converters. There is a converter for each application and I agree with you Andrew. All converters have slip until lock-up speed however, as if you locked up in 1st gear, you’d more than likely stall out due to lttle to no torque to get moving. For the OP, it’s better for him to stay stock, absolultley.
an offroad vehicle with a tighter converter will by its own very nature have lower gears. Overtight converter in a car with crappy gears like 2.73 makes for one horrible experience off a stoplight. At speed would indicates its in a higher gear. That transmission should lock in 3rd and 4th gear if I remember right. Did you notice how the tighter the converter, the harder a vehicle shifts ? Also blow off the tires easier unless its a gutless car then it just bogs like its in mud. LOL
[quote=”andrewbutton442″ post=130867]an offroad vehicle with a tighter converter will by its own very nature have lower gears. Overtight converter in a car with crappy gears like 2.73 makes for one horrible experience off a stoplight. At speed would indicates its in a higher gear. That transmission should lock in 3rd and 4th gear if I remember right. Did you notice how the tighter the converter, the harder a vehicle shifts ? Also blow off the tires easier unless its a gutless car then it just bogs like its in mud. LOL[/quote] You are correct on all counts. To clarify things, the converter CLUTCH will lock up in 3rd and 4th. Coupling speed is actually different however which is what stall determines. The impeller(connected to the engine) and the turbine(connected to the tranny) couple(match speed and transfer power) at certain rpms. You also have a stator that provides the vortex flow(power). Coupling is not equivalent to converter lock up. A high geared car(low numbers) would be a total dog with a low stall converter…exactly.
Converter becomes direct drive with locked clutch converter. Like connecting crank flange to fluid pump in essence.
[quote=”andrewbutton442″ post=130894]Converter becomes direct drive with locked clutch converter. Like connecting crank flange to fluid pump in essence.[/quote] That is correct. Unless locked up, it is fluid drive. The converter clutch creates a mechanical link.
Here is my loose converter story. In my previous LSX car, I had a 4L60E. It was beat on MERCILESSLY. 400 rwh hp being thrown thrown at for like 4 seasons of racing. Come to change the fluid, and it was clean, I mean it could have been rebottled. 60′ time was bad, like a 1.9 with a nasty sticky NItto tire. This of course is with a 4.10 gear and 3.06 first. Decided to have a converter for the street built for it, 4000 ish, and it dropped my 60 to a 1.79 gained 6 tenths in the quarter, and made go from a normally strong car to something that felt like it was going to launch into orbit. We gained 90 feet of torque the rear wheels putting around 500 for torque at the rear, however it would cook the fluid I mean black and toasty, throw all sorts of shift A and B codes 4 type codes for slipping, just a mess. I sold it to a friend of mine who employs a tranny guy, and I told him all this, and this thing needs transfluid changes ALL the time, else you will be burn it down totally. He of course hadn’t change the fluid in an entire season, and its already slowed down 2 tenths, and have to wonder about this. Clutch packs being broiled for sure. I finally broke down and bought the same year and model or car but with a 6 speed, and I have to say that first car with a stalled automatic will literally kill me in the quarter mile, no comparison, (my stick car will not even crack 2.0 in a quarter 60′ 3.42s with a 2 ratio something first, yuck) but I could not stand the fact that I could slow the car down a bunch and save the tranny, or have it be a self destructive machine.
[quote=”andrewbutton442″ post=130898]Here is my loose converter story. In my previous LSX car, I had a 4L60E. It was beat on MERCILESSLY. 400 rwh hp being thrown thrown at for like 4 seasons of racing. Come to change the fluid, and it was clean, I mean it could have been rebottled. 60′ time was bad, like a 1.9 with a nasty sticky NItto tire. This of course is with a 4.10 gear and 3.06 first. Decided to have a converter for the street built for it, 4000 ish, and it dropped my 60 to a 1.79 gained 6 tenths in the quarter, and made go from a normally strong car to something that felt like it was going to launch into orbit. We gained 90 feet of torque the rear wheels putting around 500 for torque at the rear, however it would cook the fluid I mean black and toasty, throw all sorts of shift A and B codes 4 type codes for slipping, just a mess. I sold it to a friend of mine who employs a tranny guy, and I told him all this, and this thing needs transfluid changes ALL the time, else you will be burn it down totally. He of course hadn’t change the fluid in an entire season, and its already slowed down 2 tenths, and have to wonder about this. Clutch packs being broiled for sure. I finally broke down and bought the same year and model or car but with a 6 speed, and I have to say that first car with a stalled automatic will literally kill me in the quarter mile, no comparison, (my stick car will not even crack 2.0 in a quarter 60′ 3.42s with a 2 ratio something first, yuck) but I could not stand the fact that I could slow the car down a bunch and save the tranny, or have it be a self destructive machine.[/quote]Oh ya, a loose converter requires a nice big cooler, and even then the fluid still experiences more wear. The speed between the impeller and turbine are at more of a differential hence more slippage and more heat.
Why would anybody do such a thing as more leading to more heat. At another place and time I took a 69 Impala with a 300 hp 350 with a carb that literally would not accelerator its way out of a paper sack, Crapcanned the original engine Took a late model aluminum headed LT1 SBC with from a Camaro and put a huge roller cam and all the other tricks in it, and of course of a super loose stall, and that car literally was painful in the neck because of the ridiculously loose converter and full line pressure 4L60e trans. Wouldn’t have it any other way then or now, not a chance. Big cams and tight converters are imcompatible. Over about 224- 230 on the duration and a loose converter is mandatory, trans heat or not. I had a tach with a shift light in, and the little plastic cover fell off and so it was an exposed bulb, and every time that car hit redline of about 6500 (which with a nasty loose converter, was over and over and over again) that whole inside of the car would light up because of the tach light and it had 3 inch straight through exhaust and the cops would come around looking for a fast looking car, never suspecting my boat was the culprit. Joys of stalls. At the Night drags sometimes you can see the driver come off the line the red rpm light come on and light up the driver, great stuff.
[quote=”andrewbutton442″ post=130908]Why would anybody do such a thing as more leading to more heat. At another place and time I took a 69 Impala with a 300 hp 350 with a carb that literally would not accelerator its way out of a paper sack, Crapcanned the original engine Took a late model aluminum headed LT1 SBC with from a Camaro and put a huge roller cam and all the other tricks in it, and of course of a super loose stall, and that car literally was painful in the neck because of the ridiculously loose converter and full line pressure 4L60e trans. Wouldn’t have it any other way then or now, not a chance. Big cams and tight converters are imcompatible. Over about 224- 230 on the duration and a loose converter is mandatory, trans heat or not. I had a tach with a shift light in, and the little plastic cover fell off and so it was an exposed bulb, and every time that car hit redline of about 6500 (which with a nasty loose converter, was over and over and over again) that whole inside of the car would light up because of the tach light and it had 3 inch straight through exhaust and the cops would come around looking for a fast looking car, never suspecting my boat was the culprit. Joys of stalls. At the Night drags sometimes you can see the driver come off the line the red rpm light come on and light up the driver, great stuff.[/quote] Well the physics are the physics…a high stall converter WILL lead to more heat. It also leads to more launching power as you said. Trust me, I’ve used high and low stall converters in multiple applications. I had a performance truck in college cammed with a high stall converter and a built 4L60-E trans. Until I added a bigger cooler, it always ran on the hot side, but it burned tires and launched like nobodys business.
- You must be logged in to reply to this topic.