Automatic Transmissions Revisited
03-12-2003, 11:59 PM
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Automatic Transmissions Revisited
I work at a speed shop as some of you know. I've also built and been around hot rods and engine building for 25 years. :yesnod:
Yet the term "stall speed" has always eluded a good description. Today I was talking to a guy that we do lots of work with back and forth. He's also got the San Diego reputation for custom rod trans mods, and building beef into the automatics in street rods.
I was discussing the decision I'm up against between spending money on a stall convertor for my Turbo 350 or just lowering the gears in the rear as I've done in so many other cars that had automatics. Looking for that hole shot! :yesnod: :smash: :lol:
He drove my car a few miles and said "heck I can't get this thing to stall!" to which I said "huh??" :conehead
He said the rubber keeps turning :party: !!!!!!!!!!!!!!!!!!!
So I just had to ask: PLEASE DEFINE STALL SPEED!! In English! He motioned for me to follow him to his F150 and he started it up. (all stock). he put it in drive and brake torqued it at full throttle. He said "now that's the stall speed!" I say, huh?
I was always associating stall spd to the TRANS or the Convertor. NOOOOO! It is the MAX speed of the ENGINE with the convertor locked and the wheels not turning. ... apparently at full throttle (WOT)
So he's right. My car won't stall. The wheels turn :crazy: :jester because I guess the rear brakes suck??? :nono: Anyway, he then edumukated me on what a stall convertor will give me. Torque multiplication :D
With a 1750-2000 convertor (probably stock in my car) I'm getting gear multipliers of 3:08 x 1.25 for an effective axle ratio in the rear end of 4.xx upon launch.
With the same gears, and a 2500 stall convertor, the numbers are much greater: Effective rear end gears of 6.xx upon launch, assuming the convertor is coupled at the time I launch.
So if I get that stall convertor, and save my $$ for gasoline, I may not even need the lower gears and overdrive trans. Heck I never maintain more than 75MPH for more than a few miles at a time anyway!
:flag
Yet the term "stall speed" has always eluded a good description. Today I was talking to a guy that we do lots of work with back and forth. He's also got the San Diego reputation for custom rod trans mods, and building beef into the automatics in street rods.
I was discussing the decision I'm up against between spending money on a stall convertor for my Turbo 350 or just lowering the gears in the rear as I've done in so many other cars that had automatics. Looking for that hole shot! :yesnod: :smash: :lol:
He drove my car a few miles and said "heck I can't get this thing to stall!" to which I said "huh??" :conehead
He said the rubber keeps turning :party: !!!!!!!!!!!!!!!!!!!
So I just had to ask: PLEASE DEFINE STALL SPEED!! In English! He motioned for me to follow him to his F150 and he started it up. (all stock). he put it in drive and brake torqued it at full throttle. He said "now that's the stall speed!" I say, huh?
I was always associating stall spd to the TRANS or the Convertor. NOOOOO! It is the MAX speed of the ENGINE with the convertor locked and the wheels not turning. ... apparently at full throttle (WOT)
So he's right. My car won't stall. The wheels turn :crazy: :jester because I guess the rear brakes suck??? :nono: Anyway, he then edumukated me on what a stall convertor will give me. Torque multiplication :D
With a 1750-2000 convertor (probably stock in my car) I'm getting gear multipliers of 3:08 x 1.25 for an effective axle ratio in the rear end of 4.xx upon launch.
With the same gears, and a 2500 stall convertor, the numbers are much greater: Effective rear end gears of 6.xx upon launch, assuming the convertor is coupled at the time I launch.
So if I get that stall convertor, and save my $$ for gasoline, I may not even need the lower gears and overdrive trans. Heck I never maintain more than 75MPH for more than a few miles at a time anyway!
:flag
03-13-2003, 01:23 AM
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Re: Automatic Transmissions Revisited (SanDiegoPaul)
Okay Paul I'll revisit this tommorow at work. I've had one too many beers and you just blew me away.
:skep: :smash:
:skep: :smash:
03-13-2003, 08:48 AM
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Re: Automatic Transmissions Revisited (SanDiegoPaul)
Suppose you want to find stall speed & put an auto. 350 C.I. car in gear, hold the brakes & mash down slowly on the gas, the rpm will increase until the engine stalls, i.e. the rpm will not increase further. Let's say 1800 in this example, so that's stall speed. In this ex., you could have just floored it.
Now stroke to 383 C.I. for example & do it again. Remember you are holding the brakes, this time rpm increases as you mash slowly on the gas & at 2000 rpm the engine's TQ overcomes the traction & brakes & starts to spin the tire(s). Stall speed is 2000.
:cool:
Now stroke to 383 C.I. for example & do it again. Remember you are holding the brakes, this time rpm increases as you mash slowly on the gas & at 2000 rpm the engine's TQ overcomes the traction & brakes & starts to spin the tire(s). Stall speed is 2000.
:cool:
03-13-2003, 10:12 AM
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Re: Automatic Transmissions Revisited (Ganey)
Suppose you want to find stall speed & put an auto. 350 C.I. car in gear, hold the brakes & mash down slowly on the gas, the rpm will increase until the engine stalls, i.e. the rpm will not increase further. Let's say 1800 in this example, so that's stall speed. In this ex., you could have just floored it.
Now stroke to 383 C.I. for example & do it again. Remember you are holding the brakes, this time rpm increases as you mash slowly on the gas & at 2000 rpm the engine's TQ overcomes the traction & brakes & starts to spin the tire(s). Stall speed is 2000.
No question about it, the stall changes with the application. If you read up on convertors, you'll see that they offer a range usually........such as 1800-2200 or 2750 to 3000 rpm stalls.
Now stroke to 383 C.I. for example & do it again. Remember you are holding the brakes, this time rpm increases as you mash slowly on the gas & at 2000 rpm the engine's TQ overcomes the traction & brakes & starts to spin the tire(s). Stall speed is 2000.
No question about it, the stall changes with the application. If you read up on convertors, you'll see that they offer a range usually........such as 1800-2200 or 2750 to 3000 rpm stalls.
03-13-2003, 10:23 AM
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Re: Automatic Transmissions Revisited (SanDiegoPaul)
Stall speed varies from brand-to-brand. Use it as a point of comparison only among 1 brand's converters.
The stock converter has an extremely low stall speed. With my stock tranny, it was so low that it would drag down the engine significantly at idle! Now that I have a 2200 stall converter behind my OD tranny, the problem has gone away.
If you don't do very much freeway driving, you don't need OD. Here in Texas, we do a LOT of high-speed freeway runs in 100+ degree conditions, so the OD was a complete no-brainer for me! :yesnod:
The stock converter has an extremely low stall speed. With my stock tranny, it was so low that it would drag down the engine significantly at idle! Now that I have a 2200 stall converter behind my OD tranny, the problem has gone away.
If you don't do very much freeway driving, you don't need OD. Here in Texas, we do a LOT of high-speed freeway runs in 100+ degree conditions, so the OD was a complete no-brainer for me! :yesnod:
03-13-2003, 01:11 PM
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Re: Automatic Transmissions Revisited (page62)
If you don't do very much freeway driving, you don't need OD. Here in Texas, we do a LOT of high-speed freeway runs in 100+ degree conditions, so the OD was a complete no-brainer for me!
Yea but I do a lot of BOTH! Weekends it's all about freeway trips and around town during the week. I've decided for the stall convertor. I ordered a 2500 and today it's getting the shift kit! :hurray: :party: :hurray:
[Modified by SanDiegoPaul, 10:11 AM 3/13/2003]
Yea but I do a lot of BOTH! Weekends it's all about freeway trips and around town during the week. I've decided for the stall convertor. I ordered a 2500 and today it's getting the shift kit! :hurray: :party: :hurray:
[Modified by SanDiegoPaul, 10:11 AM 3/13/2003]
03-13-2003, 01:35 PM
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Re: Automatic Transmissions Revisited (SanDiegoPaul)
If you don't do very much freeway driving, you don't need OD. Here in Texas, we do a LOT of high-speed freeway runs in 100+ degree conditions, so the OD was a complete no-brainer for me!
Yea but I do a lot of BOTH! Weekends it's all about freeway trips and around town during the week. I've decided for the stall convertor. I ordered a 2500 and today it's getting the shift kit! :hurray: :party: :hurray:
[Modified by SanDiegoPaul, 10:11 AM 3/13/2003]
Yea but I do a lot of BOTH! Weekends it's all about freeway trips and around town during the week. I've decided for the stall convertor. I ordered a 2500 and today it's getting the shift kit! :hurray: :party: :hurray:
[Modified by SanDiegoPaul, 10:11 AM 3/13/2003]
