Home › Q&A › Transmissions

What stall speed torque converter should I run behind an LS1/LS3/5.3 in an off-road rig with a TH400 or TH350?

There's no single number — the right stall depends on the whole combination. Converter makers pick it from your specs, so collect them before calling.

What sets the right stall speed (Speedway):

Stall speed is how far the engine revs against the brakes before the wheels turn. A 2,700–3,000 converter should footbrake-stall to about 2,700 rpm depending on the vehicle.
Match it to the power curve. You want the converter to lock up where the engine starts making real torque, so a bigger cam wants more stall.
Resistance raises stall: a heavy vehicle, large-diameter tires and taller (numerically lower) gears push stall up; a light vehicle with short gears and small tires brings it down.
Give the converter maker everything: vehicle weight, displacement, compression, cam specs, rear gear, tire diameter, fuel system, and transmission model and year.
Speedway's examples: a 2,800 lb street rod with a mild-cam 350 and 3.50 gears → 2,000–2,200 stall. A 3,350 lb car with a rough-idle cam, 10.5:1 383 and 4.11 gears → 3,200–3,500 stall.

Off-road rigs usually have big tires, which add resistance and raise the effective stall. Tell the converter maker the tire diameter and gearing, not just the engine. TH350 and TH400 converters also need the right flexplate setup on an LS — see what flexplate a TH350 needs.

What we recommend

For an off-road rig we recommend a stall in the 2,200-3,000 rpm range, with 2,500 as a good middle. Expect 500+ rpm less effective stall in low range, so going slightly higher than you think still crawls well. Too low (1,200-1,800) runs cool and crawls well but can stall the engine and push through the brakes, while too small a converter builds heat; in the builds we've seen, a 10 in at ~3,100 brake stall ran hot and a custom 11 in Hughes at ~2,700 ran much cooler with better crawling torque multiplication. For trail rigs, keep converter diameter large (12 in) at around 2,200 stall, and always run a good trans cooler with a fan.

Check this first:

Confirm flexplate/converter fit (a TH400 converter may need the GM flexplate spacer and 4L80E flexplate with elongated holes)
Plan a trans cooler with a fan
Factor vehicle weight and tire size into stall choice

Careful: An undersized converter builds excessive heat, which can cook the transmission on the trail.

Based on what we've seen work across our own builds, our friends' builds and the wider LS community, reviewed by our lead tuner (20 years of LS tuning). Every combination is different, so use at your own risk and check our safe tuning limits before any wide-open pass.

Go deeper

Check this first

Note the cam specs and where the engine makes torque.
Check current stall behavior: does it creep excessively at idle in gear?
Verify trans temps - a loose converter makes a lot of heat at crawl speed.

We may earn a commission when you buy through links on this page.

Try this, then this

1) Stock to mild cam: ~1,800-2,000 stall (Hughes GM20 style) - crawls well, holds on brakes.
2) Bigger cam: step stall with the cam per the JEGS chart (2,300-2,700 for 265-280 deg cams).
3) Add a large auxiliary cooler with thermostat-controlled fan; heat is the enemy at crawl speed.

How you know it's fixed

Rig holds still on the brakes in gear, crawls technical sections without excessive throttle, temps stay sane.

Still not fixed?

If it still pushes through the brakes, the stall is too loose for the combo - go tighter, not looser.

Every option we know of

Maker / product	Part #	Fits	Price	Where	Status / notes
TCI Automotive Saturday Night Special / Breakaway converters	varies by stall	TH350/TH400	about $400-700	Summit, Jegs	Current production Pick stall from the application chart, not by guess
Circle D Specialties Custom off-road converters	built to order	TH400/4L80E	$800+	Circle D direct	Built to order Call with cam specs and vehicle weight
JEGS (chart reference) Stall selection chart	n/a	2300-2700 stall for 265-280 deg cams; 3000-3400 for 280-300 deg cams	Free	JEGS	Available Chart assumes typical gearing - adjust for 3.00-3.73 gears

Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.