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Author
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Topic: Math question
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SundanceKid
Gearhead Posts: 1001
From: UT
Registered: Feb 2001
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posted 07-26-2002 04:30 PM
   
If a Tremec 3550 is rated at 375ft/lbs at 5,500 GVW What would it be rated at for a car that has a GVW of 2,800?I tried to figure it out, and came up with some wierd numbers that can't be right. Thanks
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Scott (69Mach)
Gearhead Posts: 451
From: Walnut Creek, CA USA
Registered: Jun 99
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posted 07-26-2002 05:33 PM
It seems to me it's the same. The only difference is that lighter car will accelerate quicker at the 375 ft-lbs applied torque. The heavier car may get you to the 375 limit faster due to its larger mass resisting forward motion.But heck, what do I know. 
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steve'66
Gearhead Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 07-26-2002 06:20 PM
I agree with Scott,Vehicle weight doesn't matter, if you can hook the lighter vehicle and generate 375#s of torque the tranny will still see 375#s of torque no matter what the car weighs.  SteveW
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Dusty Kiser
Gearhead Posts: 126
From: Bethel,Oh USA
Registered: Mar 2002
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posted 07-26-2002 11:42 PM
Watch out! You're thinking too hard, as I often do only to find the answer is so simple it's absurd. Torgue capacity is a given. How and when it's achieved is the variable. The lighter vehicle should be easier to accellerate so should require less torque output to achieve a given velocity in a given time. However, you can still reach maximum capacity quite easily by by reducing the time or velocity factor. Many moons ago when Generic Motors brass aproached Duntov about a V8 for the Corvette they stipulated it had to mate up to the existing 6 popper drivetrain that had very limited torque capacity. Duntov reasoned a short stroke engine could produce less torque but still make decent horsepower by turning more RPM and thus was born the concept of the first successful oversquare engine in the form of the small block Chev.
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jkilroy
Gearhead Posts: 1719
From: Vicksburg, MS
Registered: Dec 99
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posted 07-28-2002 12:53 AM
Transmissions are tested in static conditions, not dynamic. Basically they bolt an output shaft up solid and start applying torque to the input and see what goes boom. In actual use most stick transmissions can handle a lot more power than they are rated for. The other thing is, if you can't hook up, you won't break nearly as many parts.------------------
Jay Kilroy
68' Fastback GT 390
"No such thing as a cam thats too big"
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Larry Jennings
Gearhead Posts: 540
From: Redwood City, Ca. USA
Registered: Apr 2000
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posted 07-28-2002 02:55 AM
An engineer buddy was privy (as a soundboard) to the developement of the plastic cased 4 cylinder front wheel drive car trans/diff deals. He said they had the motor torque at less than half of the trans test figure and the cases would break in about 10,000 miles. One of the junior staff engineers had the answer but couldn't get the the "smart" guys to listen so he built his own test car and brought it to the lab pre-tested with 30,000+ miles on it but this was after the plastic cased cars with known problems were released, bought by the people that never figure out what GM stands for, broken many times and ultimatly bought back in a class action suit. The Jr engineer used the junk 4 banger transaxle with a 6 cylinder engine at the full test torque output and it lived because he reduced or broke the impulses into smaller units so he could use harder but smaller impulses. Later the info was used for higher output V10s with lighter weight drive trains. ------------------
Advertising is the science of arresting the human intelligence long enough to get money from it. Stephen Leacock
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SundanceKid
Gearhead Posts: 1001
From: UT
Registered: Feb 2001
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posted 08-06-2002 02:37 AM
Ok, I see? Can someone explain why they rate the T-5 at 320ft/lbs @ 3200 and the Tremec at 375ft/lbs @ 5500 GVW? Why do they use differant GVW?
My thinking (half the problem) was that the torque limit would be divisable by the GVW. More torque is required to move a heavier vehicle ect. I guess the differant torques at differant weights lead me to belive there was a differant scale. Like when you flow test at differant in. H2O??
The only reason I even looked into the torque capacity of the Tremec, is that there are so many advertised torque ratings for the same transmission. Anywhere from 375 ft/lbs. to 525 ft/lbs. for the Tremec 3550 and 25 ft/lbs more respectively for the TKO.Just wonder how they get there adjusted torque capacities?
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Rustang
Gearhead Posts: 471
From: Clarion PA
Registered: Nov 2000
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posted 08-06-2002 04:49 AM
Where did you get the torque capacity info from? Are you sure it's GVW (Gross vehicle weight)?
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bluestreek
Gearhead Posts: 1289
From: Athens,GA
Registered: Jul 2001
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posted 08-06-2002 08:18 AM
To my way of thinking, they should be rated for "input shaft" torque.
Vehicle weight only comes into play after the torque leaves the tranny. In other words, 2 vehicles with the same engine torque output, but different weights, will put the same stress on a transmission at the same torque level. BUT....They will have different acceleration rates, if gear ratios, rpms, and traction remains constant.
Now, if one of these engines has a higher rpm level for the same amount of torque, Then their will be more frictional stress placed on the bearings.
Also, if one tranny has different ratios, then the tranny with the lower gears and best torque multiplication wont have to work as hard but will require higher rpms. It's more complicated than you think. One last observation:
A heavier vehicle will place more stress on the tranny over a period of time, because the torque output must remain higher to achieve a certain speed. Now, I'm confused!! [This message has been edited by bluestreek (edited 08-06-2002).]
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Rustang1
Gearhead Posts: 110
From:
Registered: Nov 2000
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posted 08-06-2002 01:01 PM
Did some figuring. If those numbers were RPM instead of GVW, then the Tremec would be rated at 393HP and the T5 would be rated at 195HP. We have gearbox catalogs here at work and the gearboxes all have a torque rating at a given RPM. That's why I wonder if maybe that's RPM and not GVW you're looking at???
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70boss302
Gearhead Posts: 165
From: Jeffersonville, NY USA
Registered: Mar 2002
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posted 08-06-2002 06:55 PM
If you lower the resistance on the output end via car weight, you can successfully raise the input on the other end via HP. I didn't do the math here, but I would guess it to be about 500 ft lbs. Bill
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SundanceKid
Gearhead Posts: 1001
From: UT
Registered: Feb 2001
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posted 08-11-2002 02:28 PM
T-5 stats here:
http://www.ttcautomotive.com/products/T-5.asp3550 and TKO stats here:
http://www.ttcautomotive.com/products/TR-3550.asp
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SundanceKid
Gearhead Posts: 1001
From: UT
Registered: Feb 2001
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posted 08-11-2002 02:29 PM
Both say GVW...I would assume that means Gross Vehicle Weight?
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SundanceKid
Gearhead Posts: 1001
From: UT
Registered: Feb 2001
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posted 08-11-2002 02:31 PM
Ok, now I see it could be read as maximum GVW? I dono, take a look.
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