Torque Converter and Turbo...

[Monzsta]

When my Lumina was stock with the 3100 in it the torque converter would stall to about 2600-2700 rpm. Then I dropped the 3400 in there with a FAFB converter anticipating 3000-3200 stall speeds. When I saw 3700 rpm my jaw hit the floor.

Fast forward to today. Doing a highway pull while destroying a Honda the trans began a nasty slip shudder as I was going WOT in 4th. I lifted and have been babying it ever since. The trans is coming out in a week or two so I can stuff some Z-Pack clutches in it and do some mods to the valve body as well as install the 3.73 chain and sprockets. And finally fix my leaking axle seal.

My question is I'll be turboing this thing someday, and I want to pick the right converter for that while the trans is out. From what I've read, a turbo engine actually favors a lower stall speed, but I wanted to put it out there for those running a turbo with a 4T60-e

[robertisaar]

not turbo'd yet, but yes a turbo does like a lower stall speed.

this is due to the way turbos operate: they make boost under load. when you stick a high-stall convertor in there, it essentially lowers your gearing even more, and removes load as a result. when the whole vehicle catches up to the convertor and it isn't under its stall point, then its no different than the stock convertor. but i would prefer boost by 2500 with my foot to the floor, so i really wouldn't go higher than that or else you'll have to literally wait for the engine to rev high enough to put the vehicle in enough load to make boost.

[IsaacHayes]

Stock L body 4t60-e converter is really low stall. The gearing is really high (low ratio) too. Makes performance suck. I can only imagine what I would have with a W body trans.

Anyway, you have the K factor with TC's and yes more output means higher stall. Loner had his corsica with a turbo and stock L body trans as far as I know and he kept blowing them up but there wasn't much lag at all with his car from what I remember hearing.

[Monzsta]

If I put a stock converter back in there I'll be looking at 2700-2900 stall speeds. And given the nature of a turbo engine, I may hold off on putting the 3.73 set in there. My reasoning for the gears was to tighten the rpm drop between gears, but a turbo's added torque would probably favor a taller gear. I drove a 3100 Malibu once and marveled how it couldn't get out of it's own way when you floored it. I think it stalled around 1700 rpm.

[robertisaar]

correct, turbos like taller gears, a side benefit of which is better fuel economy and less engine wear (when not in boost anyway). it essentially lowers your boost threshold, so you could start making boost before you get out of first gear with a stock gear, but would need to be at 3K in second with a shorter gear. just how it goes, but i'm not complaining. especially when you're at ~55MPH, put your foot to the floor and there is instant boost. its almost like an extra downshift...

and then there is always the possibility of the turbo making too much torque for the tires to handle, especially when combined with a numerically higher gear.