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SemperFly
 
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Quote:
Originally Posted by why_ask_why
I don't think top fuel dragsters even have 2600+lb ft
dude they can't even be measured

that's why top fuel power numbers are always "estimated"...no dyno in the world can measure 6000+ horsies
Old 08-30-2004, 02:48 PM SemperFly is offline  
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Why_Ask_Why
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Quote:
Originally Posted by demosh
But I am talking about wheel torque. .

Quote:
Originally Posted by demosh
Engine torque, not "wtq"

regardless of where the numbers are coming from they are DEAD WRONG...your saab 900 is making nowhere near what you are suggesting...you don't need to be a rocket scientist to figure that out, it's just common sense
Old 08-30-2004, 02:49 PM Why_Ask_Why is offline  
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Quote:
Originally Posted by LagPenguin
Because you're multiplying the final drive.

He is correct, for first gear (or any other gear, for that matter).

Dyno's *need* the 1:1 gear ration, to get as accurate a reading as possible, but that still doesn't explain the numbers it generates.
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Old 08-30-2004, 02:50 PM Tex Arcana is offline  
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Quote:
Originally Posted by LagPenguin
Because you're multiplying the final drive.

Yes, because that gives the torque at the wheels.
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Old 08-30-2004, 02:50 PM demosh is offline  
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Quote:
Originally Posted by demosh
Engine torque, not "wtq"
hi, dumbass

300 wheel torque does NOT take drive ratios into account. that's why you drive the fucking car to the 1:1 gear and if there's no exact gear the computer's programmed to adjust for each particular car

you're trying to talk about physics when you have no fucking clue how power figures in cars are measured
Old 08-30-2004, 02:50 PM SemperFly is offline  
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Tex Arcana
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Quote:
Originally Posted by LagPenguin
Because you're multiplying the final drive.

He is correct, for first gear (or any other gear, for that matter).

Dyno's *need* the 1:1 gear ratio, to get as accurate a reading as possible, but that still doesn't explain the numbers it generates.
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Old 08-30-2004, 02:50 PM Tex Arcana is offline  
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Quote:
Originally Posted by Tex Arcana
And since it's well-known that gear ratios multiply torque, the question remains: where is the discrepancy??
Chassis dynos are programmed to take your gear ratios into account and adjust the numbers accordingly.
Old 08-30-2004, 02:51 PM SemperFly is offline  
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Quote:
Originally Posted by FlyNavy
hi, dumbass

300 wheel torque does NOT take drive ratios into account. that's why you drive the fucking car to the 1:1 gear and if there's no exact gear the computer's programmed to adjust for each particular car

you're trying to talk about physics when you have no fucking clue how power figures in cars are measured

If you are so damned well versed in how they're measured, then enlighten us, and please dont forget to take into account the final drive ratios.
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Old 08-30-2004, 02:51 PM Tex Arcana is offline  
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Quote:
Originally Posted by demosh
But I am talking about wheel torque. And those are the numbers at the wheels in first gear in Saab 900s when the engine is at its torque peak. I fail to see any mistakes in my calculations.
because torque numbers are NEVER given in first gear
Old 08-30-2004, 02:53 PM SemperFly is offline  
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Quote:
Originally Posted by Tex Arcana
If you are so damned well versed in how they're measured, then enlighten us, and please dont forget to take into account the final drive ratios.
Quote:
Originally Posted by FlyNavy
Chassis dynos are programmed to take your gear ratios into account and adjust the numbers accordingly.


If you put your truck on a dyno with the information for say...a 94 Accord, your final numbers would be way off because it's taking into the account the final drive ratio for the car it's been programmed for. This is why chassis dynos are hooked up to computers.
Old 08-30-2004, 02:54 PM SemperFly is offline  
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here's a chart on the saab 900's specs /thread derail
http://www.histomobile.com/1/Saab/19...edan.htm?lan=1
Old 08-30-2004, 02:55 PM Why_Ask_Why is offline  
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Quote:
Originally Posted by why_ask_why
regardless of where the numbers are coming from they are DEAD WRONG...your saab 900 is making nowhere near what you are suggesting...you don't need to be a rocket scientist to figure that out, it's just common sense

Er

At the engine it is making 194 lbs-ft. In first gear, that translates to 2653 lbs-ft at the wheels. In a 1:1 gear, it makes for 741 lbs-ft at the wheels.

At the torque peak, this particular engine is spinning at 2100 rpm (IIRC, but the actual number isnt relevant). In first gear, the wheels are spinning at 2100 rpm / 3.58 / 3.82 = 154 rpm
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Old 08-30-2004, 02:56 PM demosh is offline  
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Quote:
Originally Posted by FlyNavy
Chassis dynos are programmed to take your gear ratios into account and adjust the numbers accordingly.

Then the numbers they spew out are not "wheel" numbers.

Let's try this again, using my truck as an example: 450 ft-lbs of torque at the crank, thru 1:1 in the tranny, assuming no losses and a locked torque convertor, thru the 1:3.73 rear-end ratio (which will multiply the torque 3.73 times, ignoring the differential), then thru the wheels (which will divide the torque by 1.19, becasue it's over a lever arm of 1.19 ft), which will produce 757 ft-lbs at each wheel, or a total of 1514 ft-lbs.

but the dyno sez 425 ft-lbs at the wheels.

Discrepancy.

So where is the error?
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Old 08-30-2004, 02:57 PM Tex Arcana is offline  
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Quote:
Originally Posted by demosh
Er

At the engine it is making 194 lbs-ft. In first gear, that translates to 2653 lbs-ft at the wheels. In a 1:1 gear, it makes for 741 lbs-ft at the wheels.

At the torque peak, this particular engine is spinning at 2100 rpm (IIRC, but the actual number isnt relevant). In first gear, the wheels are spinning at 2100 rpm / 3.58 / 3.82 = 154 rpm
You're fucking wrong. It does not make for 741ftlbs at the wheels. You can throw math and physics all you want but when the numbers are fucking MEASURED the final drive ratio is taken into account by the dynos computer and adjusted.

You put your fucking Saab on a dyno and you will never see 741 ft lbs. Period. Ever.

Why the HELL are you talking about first gear? Who gives two flying shits about first gear when all cars, every last fucking one, is always measured in the gear closest to 1:1.
Old 08-30-2004, 02:57 PM SemperFly is offline  
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Quote:
Originally Posted by demosh
Er

At the engine it is making 194 lbs-ft. In first gear, that translates to 2653 lbs-ft at the wheels. In a 1:1 gear, it makes for 741 lbs-ft at the wheels.

At the torque peak, this particular engine is spinning at 2100 rpm (IIRC, but the actual number isnt relevant). In first gear, the wheels are spinning at 2100 rpm / 3.58 / 3.82 = 154 rpm

you don't dyno a car in 1st gear...you use the 1:1 ratio gear which is generally 4th
and this has already been said a zillion times
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