How important is "Launch Ratio"?

http://www.5speedtransmissions.com/startlineratio.html

How important is starting line ratio or another name, launch ratio? Mainly referring to automatic transmissions.

I first read about this in my Powerglide rebuild book and then I researched this and found the above link. For example: An 8.5 Chevy with 3.42 rear gears and a 700r4's 3.06 starting gear would keep the launch ratio at 10.46 which is what the above link says is desirable. I asked about this on a different forum and I don't think they have ever heard about launch ratio but they said a bigger rear gear develops a harder launch. Is this true? With 4.10's the starting line ratio is at 12.54 with a 700r4 3.06 first gear. 5speedtransmissions.com said that this would be a negative for a hard launch.

What I am looking for is the hardest launch I can get with the available money I have to spend. In closing, what is more important for a harder launch, a bigger gear or launch ratio in the desirable range?

I asked on another forum and they said that 10:1 ratio is a good compromise. Anywhere much higher will blow the tires off, much lower will pull the engine down. That's only one reply so does anyone else have an idea?

If you are wanting a really hard launch then save up and buy a trans brake.

Another thing is I think you are looking too hard into what you are doing. Get the car running and work your way up the ladder. When we all first started driving and racing we was really happy with a 15 second pass. Most of our cars were rainy day hot rods. Then some started breaking into the 14's. yeah I know that is slow by todays standards but that's how it was way back then. 13's was next and so on. Some are running in the 10's now. It's okay to try to get the info you want but just getting the car out and start driving it now and working your way up will help. You learn as you go.

I'm no expert, but I agree with Admin. Run it and learn what it will do, and experiment to go quicker. I don't agree with the first scenario with the powerglide, those are just calculations with given numbers; what will have a dramatic affect is stall speed, and RPM. All torque convertors have an amount of torque multiplication built in determined by fin count, fin angle, available input torque. Calculating this is real difficult- if you have ever bought a high stall convertor you will be sold one with a stall range of 2 to 300 rpm (ex 2300 to 2500). Furthermore, if you use a t-brake your stall rating increases because the engine can develop maximum power at launch speed where it makes all its power,hopefully your cam and stall speed will do their best at a common RPM. You can't develop as much stall using the vehicle brake due to not being able to hold traction, or hold the drivetrain-- it just isn't as efficient or effective as locking two gears. As a result, only experimentation will tell you what you need to know. Guess what- vehicle weight is another variable that plays into this whole mess as well. This will probably start many conflicts in the forum, but many articles have been written on this by racers, physicists, and engineers, and if you read more than half a dozen of them your head will start spinning. If you race with an automatic, experiment with stall if you want, depends on how well you like pulling trannies- but a good tranny shop who races as well as fixes transmissions is invaluable. Keep in mind though, sooner or later everyone makes a bad call. I'm sure this didn't answer your question, but it might get you thinking about what your convertor has to do every time you drop the hammer. Good luck.

It's all important. If you want to build a dedicated track car you'll take a different approach than you would with a car you want to be able to drive and also take to the track on occasion. Launch ratio is one factor and in the range of 10 is probably a good place to start, but you also want to be able to hit RPMs just above peak HP as you cross the finish line in the 1/4 mile. None of that matters if you don't have springs and shocks that allow some decent weight transfer and that is pointless unless you have some tires that'll give you some hook out of the hole & unload w/o breaking. None of that matters if the drivetrain can't handle the abuse.

It isn't easy and there isn't a theorum or simple calculation that works for every car or every condition. Some of it just has to be done by trial & error. Some of it can be done by finding out what someone else has done with the result you want.

Get it running and driving w/o spending a bunch of money on stuff you're not sure will get you the result you want.