I sell tools for a living wholesale and I sell air impacts and electric impacts, corded impacts you get the idea. These tools are are all rated
by the torque they have. A strong 1/2 cordless impact will have close to 300ft. lbs. of torque for example. A strong 1/2 drive air impact will have 900 ft. lbs of torque. These tools are tested and measured on a tool called a skidmore. So now here's where the questions come in.
If a 1/2 air powered impact wrench can produce 900ft. lbs of torque how is it our cars are only putting roughly 300 ft. lbs to the rear wheels. I once read a post that got into a formula for how much torque a Corvette was putting to the wheels with a 3.73 rear gear and how much more it was than stock. Can one of you or several of you with a better understnading of this explain it to me ? I think many on here would find this very interesting.

 

An electric motor puts out full torque at stall, our SBCs put out (relatively) low torque at idle and peak torque at some higher RPM.

Frankly I'm surprised you can provide 900 ft-lb from a 1/2" impact tool...

 

I'd say the difference is in the gearing.

Say my nearly stock LT4 was making 330rwtq with my ZF6 and 3.45 stock rear.

That means it makes 330 flywheel tq * 2.68 (ZF6 First Gear) * 3.45 (rear end) = 3051.18 ft/lbs rw effective torque in first gear.

Same engine in 6th gear. 330 * .5 (6th Gear) * 3.45 = 569.25 ft/lbs effective torque.

Same engine with 4.11's. 330 * 2.68 * 4.11 = 3634.88 ft/lbs rw effective torque.

Same engine with 4.11's in 6th. 330 * .5 * 4.11 = 678.15 ft/lbs rw effective torque.




My new engine: 490 flywheel tq * 2.68 (ZF6 First Gear) * 3.45 (rear end) = 4530.54 ft/lbs rw effective torque in first gear.

New engine in 6th gear. 490 * .5 (6th Gear) * 3.45 = 845.25 ft/lbs rw effective torque.

New engine if it had 4.11's. 490 * 2.68 * 4.11 = 5397.25 ft/lbs rw effective torque.

New engine if it had 4.11's in 6th. 490 * .5 * 4.11 = 1006.95 ft/lbs rw effective torque.

(all these numbers are a good bit high because I based them on flywheel tq not rear wheel torque which would account for accessories and drivetrain loss).


I could be wrong, wouldn't be the first time, but hopefully someone will come by and double check me.

 

[QUOTE=Cold_B;1558474738]I'd say the difference is in the gearing.

Say my nearly stock LT4 was making 330rwtq with my ZF6 and 3.45 stock rear.

That means it makes 330 flywheel tq * 2.68 (ZF6 First Gear) * 3.45 (rear end) = 3051.18 ft/lbs rw effective torque in first gear.

Same engine in 6th gear. 330 * .5 (6th Gear) * 3.45 = 569.25 ft/lbs effective torque.

Same engine with 4.11's. 330 * 2.68 * 4.11 = 3634.88 ft/lbs rw effective torque.

Same engine with 4.11's in 6th. 330 * .5 * 4.11 = 678.15 ft/lbs rw effective torque.




My new engine: 490 flywheel tq * 2.68 (ZF6 First Gear) * 3.45 (rear end) = 4530.54 ft/lbs rw effective torque in first gear.

New engine in 6th gear. 490 * .5 (6th Gear) * 3.45 = 845.25 ft/lbs rw effective torque.

New engine if it had 4.11's. 490 * 2.68 * 4.11 = 5397.25 ft/lbs rw effective torque.

New engine if it had 4.11's in 6th. 490 * .5 * 4.11 = 1006.95 ft/lbs rw effective torque.

(all these numbers are a good bit high because I based them on flywheel tq not rear wheel torque which would account for accessories and drivetrain loss).


I could be wrong, wouldn't be the first time, but hopefully someone will come by and double check me.[/QUOTE
This is very interesting, what is the difference between effective torque and the torque numbers you get from a dyno run ?

 

The difference is that an engine can put out 300ft/lbs continuously, while an impact wrench can only put it out momentarily, during the impacts. It takes a lot of those very, very brief impacts to finally tighten a fastener to full torque (e.g 300ft/lbs).

It's analogous to a hammer: a 16oz hammer striking an object can produce a force of hundreds of pounds, but only for a millisecond.

Larry
code5coupe

 

I'm not sure that effective torque is the best term, but I don't know of one better.

I'm pretty sure that when you run a car on the dyno, they run the car in the gear thats closest to 1.0, and factor in the rear end gears. That way the get the most accurate results possible.

If a car had a 6speed manual, and had 8.00 rear gears, traction would be a major issue, probably non existant because of the multiplication of the engines torque by the transmissions's gears and rear end gears.

All things being equal, a car with rear end gears of 2.50 should be alot slower than the same car with 5.00 gears. The car with 2.50 gears will have a higher top speed, but the car with 5.00 gears will acclerate alot faster.

Another way to think of it would be with you turning a bolt. You can only make so much torque with just using your hand and arm, but you can apply alot more torque with a socket and wrench. And if you added a breaker bar to the end of the wrench, to extend it, you can apply alot more torque, but your going to have a hard time turning the wrench very very quickly.

 

This is why.

Its like having a wrench on a bolt and a hammer pounding on it to loosen that stuck bolt- impact wrench style or just pulling on it with constant force of your hand like the car does on a dyno.

 

 

Aren't most tools rated in in/lbs? Most tightening specs for nut and bolts usuall give you in/lbs figures.

 

Some small nuts & bolts are rated in lbs-in but most I've worked with on the Vette have been in lbs-ft.

 

I'm surpized no-one has mentioned power yet (at least that I saw)

Anyway, I personally probally wouldn't have a problem making 300ft-lbs of torque with a breaker bar.. HOWEVER I cannot move a car like a LT1 can..

Why? cause I don't have the POWer

 

I would call the torque at the rear wheels RWTQ. Unfortunately, that term is already used to mean "engine torque extrapolated from RWTQ," so it would get confusing...

 

Only very small (6mm, 1/4", etc.) fasteners call for inch/pounds. Even these are where very precise torque values are called for, e.g. knock sensor fasteners, small fasteners threaded into aluminum, etc.

Check the torque values in any automotive service manual, 99% are in foot/lbs.

Larry

 

Larry is exactly right in both his posts. Momentary snaps of torque are delivered by impact guns. Most large bolts are in the ftlb range, smaller ones in the inlb range and very small fastners in electronics are in the inoz range. I've seen the jesus nut on helicopter rotor heads that take over 1000ftlbs of applied torque to tighten. They use large torque wrenchs to turn torque multipliers to do this.
Most impact guns are not accurate, they won't repeat either. Air impact guns are very dependent on the volume of the supplied air, not the pressure. Electric ones that give high ftlb torque are rare and expensive.

 

This is the way it was described to me:

1 ft lb of torque on a wrench was described as 1 lb on a one foot long bar
1 in lb of torque was 1 lb on a one inch long bar.
torque on a dyno was calculated using a water brake that applied a precise amount of resistance that was calculated by a hydraulicly applied force using a measurement of energy.
Torque is the force that pushes u into the seat, and horsepower determines how long it stays there.
It is possible to apply 300 ft lbs of torque by adding a "cheater" to a 1 foot bar by:
adding up the torque wrench torque of 100 ft lbs and a thick walled tube over the torque wrench where the total length of the torque wrench/cheater was 36 inches long.

There is dry torque where the threads of the assembly is assembled without any lubrication on the threads, and wet torque that needs lube on the threads to achieve a smooth low rotational resistance at final torque.

Wet torque usually adds about 3-5 ft.lbs of torque depending on the head size of the fastener used. The larger the fastener head, the more resistance to rotation, the lower the added wet torque.
for this reason, the fastener that is used to assemble a part should not be used for the torque application if the fastener has a nut that is accessible. (ie torque the nut not the bolt)
Wet torques include the thread and the bottom of the head of the fastener (such as a head bolt)to lessen the resistance and get a true wet torque.

 

Its not magic how a water brake dyno measures torque. A brake is attached to a lever with a load cell to a ground. The load cell is just a piece of aluminum in a Z shape with a strain gauge attached.

 

we have a ''mover'' in the race car shop...nothing more than a six foot long pipe with an end plate that fits over the lug nuts of the rear wheel...always fun to put the mover on the hub and ask a 110 lb cutie visitor to ''hold this up for a second'', walk away and say ''hold it up good'', hear the cutie scream ''the car is MOVING'' .

thats torque..

 

This is exactly why.

 

That's the best way to think of it. Sure, you can put 300lb/ft of torque onto something if you have like a 3' breaker bar or longer. But how fast can you turn it?

For example, I could turn a nut really fast with some geared crank setup, or fairly fast with a short wrench (maybe 4"). But I can't put much torque on them that way, hardly any actually. If I use a 3' breaker bar, I can put lots of torque, but I sure can't spin it fast. All I can do is take my meager ability to do work (power) and use simple things to increase the torque this meager ability can create.

An engine, however, can put out 300 lb-ft of torque at 4,000 rpm. I couldn't dream of doing that with a 3' breaker bar. A gasoline engine has a lot of power, or the ability to do work.

If you hooked your air impact wrench up to the transmission input on your car, your car would not accelerate very fast because that tool doesn't have the ability to do a lot of work.