Is my torque converter rpm safe?

[mathieu109]

Hey all. I am finally getting my k5 all buttoned up. I have a 2500rpm (so they said) stall converter in it from the last owner. My specs are 700r4, mild sbc, 4.56 on 37's. Is this rpm going to be safe for the tranny on trails for long times of slow driving and putting around or do I need to go have a stock one put in. I already can tell it sucks to get rolling but other then living with that and jumpy lockup going up small little hills (from Florida) am I going to hurt the transmission in any way?

 

[nvrenuf]

Stall converters build a lot of heat because by design they slip. Any time your driving under the stall rating, it's getting hot especially for long periods. Something to really think about is the gear ratio vs tire size, per online charts your combo will run almost 2700 rpm in 3rd gear (1:1) at 65 mph so you need to be sure the cruising rpm in overdrive is no too low.

IMO, if you're blasting through mud holes your converter would be fun but for crawling and hwy cruising something closer to stock would be better.

 

[mathieu109]

Stall converters build a lot of heat because by design they slip. Any time your driving under the stall rating, it's getting hot especially for long periods. Something to really think about is the gear ratio vs tire size, per online charts your combo will run almost 2700 rpm in 3rd gear (1:1) at 65 mph so you need to be sure the cruising rpm in overdrive is no too low.

IMO, if you're blasting through mud holes your converter would be fun but for crawling and hwy cruising something closer to stock would be better.

Stock is what I am leaning towards 100%. My cam is mild to beefy but nothing insane. Do you know the stock converter rpm? I have the option to pick a 1400-1600 one or a 1600-1800 one. I am thinking the lower one since my gear calc shows 1800 at 65 in OD but could that one stall to low?

 

[Wes Harden]

You should be locked in 4th so stall is a not an issue.
I asked for a 1600 rpm stall converter last time my 700r4 was done have almost 4k miles now. The 1600 stall works as engine brake for down hill rolls. If I need to replace my converter I am leaning towards Hughes performance GM22LXTM.
I did have an issue with getting hot towing and in traffic. I have a good rad trans cooler, a large stacked plate external cooler, with an 8" 180 deg temp controlled fan, and now a Derale cooler pan. I think I finally have the oil temps under control.

 

[mathieu109]

You should be locked in 4th so stall is a not an issue.
I asked for a 1600 rpm stall converter last time my 700r4 was done have almost 4k miles now. The 1600 stall works as engine brake for down hill rolls. If I need to replace my converter I am leaning towards Hughes performance GM22LXTM.
I did have an issue with getting hot towing and in traffic. I have a good rad trans cooler, a large stacked plate external cooler, with an 8" 180 deg temp controlled fan, and now a Derale cooler pan. I think I finally have the oil temps under control.

So the 1400-1600 should work good or would it need the extra at 1600-1800? I don't know what end of the range of those it would be on my rig.

 

[Wes Harden]

I guess it depend on your torque curve.
If your going to crawl go as low as your engine can, but still Begin to make power.

 

[mathieu109]

I guess it depend on your torque curve.
If your going to crawl go as low as your engine can, but still Begin to make power.

Sweet, I do not exactly know my curve but I think I will go with the 1400-1600 to keep heat down both at low and hwy speeds. I idle at under 1k anyways so I really doubt even with the cam it would ever stall its self out at a red light.

 

[centexk5]

Call whoever you are buying a converter from and talk to them. 1400-1600 is pretty low for a gas engine. That’s on the low range for a diesel. The gears will help some. Basically, at that rpm think of it as driving a stick and how it would feel having the clutch out at that rpm. I’d rather see a 1600-1800. 2500 is to high for sure.

 

[mathieu109]

Call whoever you are buying a converter from and talk to them. 1400-1600 is pretty low for a gas engine. That’s on the low range for a diesel. The gears will help some. Basically, at that rpm think of it as driving a stick and how it would feel having the clutch out at that rpm. I’d rather see a 1600-1800. 2500 is to high for sure.

Even with 1600 being the OD rpm with the 700r4 and my setup the 1600-1800 would be a better choice?

 

[Wes Harden]

the overdrive is not a consideration, torque converter should be locked in 4th. so no stall. You will probably never be under 1800 in third or second 1st thou you might if crawling in t case hi.

 

[mathieu109]

the overdrive is not a consideration, torque converter should be locked in 4th. so no stall. You will probably never be under 1800 in third or second 1st thou you might if crawling in t case hi.

That makes sense, kind of new to torque converters so I had to google about lockup. I am considering going with the 1600-1800 then as long as the slip under 1800 rpm if in 4 hi would not build up enough heat to cause issues. I see doing 10 in 1st would be about 1300rpm. 15 is 1900rpm.

 

[Wes Harden]

I would invest in a temp gauge for the trans. I have my sensor in the pan, so I get an average temp. The hottest oil is coming out of the torque converter, but goes straight to the cooler, then back to the pan. Some people want to know the temp coming out of the torque converter, I am not sure why. The clutches, seals, bushings and other internals never see the oil temp from the converter, unless your coolers are under size. So the oil temp in the pan is important to know that is the oil temp the other parts are running in. I have been trying to keep mine under 200. 220 is when bad stuff starts to happen. If you get over 220 change the oil as soon as you can, and figure out why the temp went over.