Ask ten drag racers which transmission to run and you might get ten different answers. Some swear by the TH400. Others wouldn’t put anything but a Powerglide in their car. Both have earned their place at the strip. The right choice depends on your weight, torque, gearing, converter, and goals.
The TH400: Three Gears and a Whole Lot of Versatility
The TH400 is a three-speed automatic with a long racing history. With a conventional gearset, first is 2.48:1, second is 1.48:1, and third is 1.00:1. That deeper first gear helps get a heavier car moving, and the additional ratio can help keep a smaller engine in its powerband.
There’s extensive aftermarket support for transbrakes, upgraded internals, and racing valve bodies. The tradeoffs include an extra shift and potentially more rotating losses, depending on how the transmissions are built. A stock TH400 is not automatically ready for serious horsepower.
STAGED Performance Take: It’s a great all-around drag transmission, particularly for heavier cars and combinations that benefit from three gears.
The Powerglide: Two Gears, Simple and Proven
A Powerglide has two forward gears. Common factory first-gear ratios are 1.76:1 or 1.82:1, with a 1.00:1 high gear. Aftermarket racing ratios are also available.
That taller first gear can help a lightweight, high-torque car manage wheel torque on the starting line. You also have one fewer shift. But a heavier, milder car may struggle with the tall starting ratio, and the larger RPM drop makes converter selection critical. A serious racing Powerglide can be expensive once you add upgraded internals.
STAGED Performance Take: It makes sense when the car has enough torque and the combination benefits from a taller first gear and fewer shifts.
TH400 vs. Powerglide: Side-by-Side
| Feature | TH400 | Powerglide |
|---|---|---|
| Forward gears | 3 | 2 |
| Common factory first gear | 2.48:1 | 1.76:1 or 1.82:1 |
| High gear | 1.00:1 | 1.00:1 |
| Shift RPM drop | Generally smaller | Generally larger |
| First-gear torque multiplication | Higher with common ratios | Lower with common ratios |
| Transbrake available | Yes | Yes |
| Aftermarket support | Extensive | Extensive |
Can You Run a TH400 Like a Two-Speed?
Here’s something worth knowing before pulling a perfectly good TH400 out of your race car: a properly configured TH400 can be set up to launch in second gear.
With conventional ratios, second gear is 1.48:1 instead of the 2.48:1 first gear. Launching in second reduces initial torque multiplication, which may help a lightweight nitrous or high-horsepower car manage traction. Some purpose-built TH400 racing configurations can also be operated as two-speed setups, depending on their design.
But There’s a Catch
Do not assume every TH400 or transbrake supports a second-gear launch. The transmission and transbrake valve body must be specifically designed or configured for that operation, with internals suited to the loads involved.
A second-gear launch also changes how the engine and converter are loaded. It won’t automatically make the car quicker. Ask a qualified racing transmission builder before trying it.
STAGED Performance Take: It may be a useful alternative to swapping transmissions, but only when the builder confirms the setup supports it.
Vehicle Weight Makes a Bigger Difference Than People Think
A lightweight turbo LS car might have plenty of torque and struggle more with traction than acceleration. A Powerglide’s taller first gear can help. A heavier street/strip truck with a mild 5.3 may benefit from the TH400’s deeper first gear and closer spacing.
Match the transmission to the vehicle, not just the horsepower number.
What About Turbo Cars?
You’ll see plenty of fast turbo cars with Powerglides, but that doesn’t make one mandatory. A smaller engine and large turbo might benefit from the TH400’s extra gear; a torquey combination may love a two-speed. Converter characteristics, boost control, and gearing also affect how the car stages and leaves.
What About Nitrous Cars?
Nitrous can add torque very quickly. A Powerglide’s taller first gear may help a lightweight car control it, while a TH400 can be excellent in heavier cars, especially with progressive nitrous delivery and a sorted suspension. Neither transmission has a monopoly on fast passes.
Let’s Talk About the Converter
Don’t overlook the torque converter. It affects how the engine loads, how quickly it reaches its powerband, and how power gets transferred during the pass. On a turbo car it also plays a major role in staging boost.
Give a reputable converter builder the vehicle weight, engine, power adder, rear gear, tire size, and intended use. That beats guessing a stall speed because somebody online recommended it.
Which One Is Cheaper?
That depends on what you own and how much power you need to hold. Include the converter, transbrake, internal upgrades, shifter, driveshaft changes, and installation when comparing costs. Switching a good TH400 just because Powerglides are popular may be money wasted.
STAGED Performance Take: Which Would We Run?
Heavier budget drag truck? We’d lean TH400.
Lightweight, high-horsepower car? We’d seriously consider the Powerglide.
Smaller turbo LS? We’d decide after looking at the converter, powerband, and gearing.
Already own a good TH400? Get some time slips before replacing it.
The bottom line: The fastest combination isn’t necessarily the one with the most expensive parts. It’s the one where everything works together.