Powerglide transmission used in racing

[NetWareHead]

So one thing I have always wondered is why are powerglide transmissions relatively popular in drag racing. Common sense dictates the low first gear should impose quite a load on the engine when accelerating. Typical gear ration for first gear are 1.76:1 or 1.82:1. I have a manual transmission car and if I tried to accelerate my car from standstill with a similar gear ratio, I would either stall or ride my clutch significantly while getting out of the hole (slowly).

Maybe it is the addition of an unusually high stall torwue converter that enables the car to overcome the low ratio first gear. Why not use a th350 or th400 for instance and benefit from an extra gear and higher ratio?

Not saying the powerglide doesn't work, some of the fastest cars on the 1/4 mile have used powerglides. Just trying to it figure out

 

[franksta]

They are able to withstand a lot of power. There are only 2 gears so less time is spent shifting. No fancy computer required. Simple, cheap, and lots of them in use.

 

[Jimzz]

Yep don't need a lot of gear to go a 1/4 mile. Also the trans gear is just 1, the gearing of the diff is the other. So if they need to change the cars overall ratio they could do so in the trans or diff.

 

[Squeetard]

Run one in my drag car for the last 15 years. They are tough and cheaper to build for high horsepower and a 3 speed. The high stall (5000 rpm) makes up for the taller 1st gear. In fact we had traction trouble off the line when we ran a 3 speed.

The other reason is they are lighter and rob quite a bit less horsepower than a 3 speed. A turbo 400 will rob 43 horses off the crank. A powerglide takes 27.

 

[monkeydelmagico]

easy to trans brake a powerglide too. Cutting a consistent light can get you the win.

lightweight cars use powerglides. Traction limited cars use powerglides. heavier cars need more gears so TH400 or, if you gots the moneys th350

powerglides are cheap (relatively)

 

[Howard]

The slippage of the torque converter provides a temporary increase in mechanical advantage. Sort of like dumping the clutch from redline in a manual (don't do that).

 

[yottabit]

Aside from simplicity it has to do with the amount of torque available and the powerband

You only need a transmission at all if you don't have enough torque available to be traction limited at your desired final drive ratio

Hence why top fuel dragsters don't have transmissions. Same concept applies to why electric cars don't need transmissions, because they provide tons of torque off idle.

Your drag race cars with powerglides tend to have pretty wide powerbands. Supercharged V8s, etc. If you have a peaky naturally aspirated motor then you'll probably want/benefit from more gears.