Higher converter stall speed to compensate for high axle ratio

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blue85, Apr 19, 2001.

  1. Blue85

    Blue85 Troll Premium Member

    Jul 26, 2000
    Likes Received:
    Grand Rapids area
    What do you guys think of the idea of using a higher stall speed in the torque converter to help make up for stock gears with oversize tires? The idea is that the higher slippage lets the engine work at higher rpms so that it is more "free" and the higher torque multiplication helps make up for the gear shortage. If you run lockup, gas mileage on the highway shouldn't be an issue. The only drawback, then, would be for low speed 4-wheeling. It would be harder to rockcrawl with, for example.

    I ran my truck for a while with stock 3.08 gears, 31" tires and stock torque converter. I upgraded to 33" tires and noticed a loss of acceleration, but it wasn't too bad. Then after my 700 bit it, I rebuilt it and ran a Corvette converter, which stalls at around 2000rpm. I noticed the added slipping right away (less "thunk" when engaging drive, more rev needed to hop over obstacles, etc.), but I wasn't really sure if it was giving me better acceleration. At first I didn't like it, but after a while I got used to it. Recently that converter stopped locking up so I took it out and put a stock stall speed back in. I've always been told that that is 1600-1700, but I think that it is actually more like 1500. Everything is a lot tighter now and the lockup works, but the truck seems like a dog. It is apparent that the engine is working a lot harder since there is now less torque multiplication in the converter and the engine rpms are always a lot lower. Now I realize that the 'Vette converter was helping to give my Jimmy better acceleration.

    After I have a 4.10 gear ratio, the stock converter may prove to be the best thing, but for the time being, I miss the higher stall speed.

    What do you guys think? Has anyone else done this?

    <font color=green>"MAN THOUGHT HURT BUT SLIGHTLY DEAD" --Providence (R.I.) Journal</font color=green>
  2. dyeager535

    dyeager535 1 ton status Premium Member

    Dec 13, 2000
    Likes Received:
    Roy WA
    I know you know to run a huge cooler, thats the ONLY downside to running a higher stall converter with numerically low gear ratio that I can think of. If you keep the stall reasonable enough, you should be ok, but if you have OD, you don't want the stall to be close to your normal (cruise) RPM's.

    I think my friend is running like a 2000RPM stall with th350 and 2.56's in his car...3800lbs, and his car will spin the tires no problem....my car, similar motor (415CID) with the lowest stall converter I could get, wouldn't even think about spinning the tires unless it was wet out.

    Its basically a trade off..truck cam is already optimized for low end torque, but with the low stall speed, trying to get over an object is a chore...with a higher stall, you get a bit more of an advantage, but at the cost of heat and less MPG, although lockup makes that negligible.

    IMO of course

    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
  3. bigerik

    bigerik 1/2 ton status

    Feb 24, 2001
    Likes Received:
    Sonoma County, CA
    I don't know enough to give an opinion, but I will relay my experience. My '76 Jimmy was a 350/TH350/NP203 with 33" tires/3.73 gears and it performed really well all around. When I made a huge number of mods (pretty much all one can do) including heavy 39" Boggers/5.13 gears, I experienced a loss in acceleration which I think is due to the added unsprung weight. It has always had the stock stall converter, but the truck is so heavy it doesn't stall until 2200-3200 rpm. I have thought about trying a higher stall in search of better acceleration. I wanted lower gears, but 5.13s are the lowest I could get for the C14FF rear. If I were you, I would jump on the 4.10s.

    <A target="_blank" HREF=http://www.bigerik.coloradoK5.com>http://www.bigerik.coloradoK5.com</A>

Share This Page