Moparts
Sure grip = 15% torque loss?
Posted By: mark7171
Sure grip = 15% torque loss? - 07/15/09 04:22 AM
I was told that over a open differential, the sure grips/or posi type can take up to 15% of the turning torque away. Also up to a certain level an open differential will get better acceleration on the street. That the torque advantage can be 2:1 at times, from a foot braked start. Knowing converters can do stall tricks , this might be something possible in the differential?
Could a mild performance build benefit from the open rear end?
Is it that you just like 2 lines?
Posted By: Nick Mineau
Re: Sure grip = 15% torque loss? - 07/15/09 04:35 AM
i would say it has to do with the car. if you can launch @ full throttle with i peg leg and not spin then the possi wont help mabe only hurt. but most cars would cook the tire and a possi will duble the traction resulting i a much faster et.
Posted By: dave571
Re: Sure grip = 15% torque loss? - 07/15/09 04:40 AM
Sorry I don't buy it.
All a limited slip unit is, is a set of spring loaded clutches, that try to hold the side gears to the carrier.
I don't see how it could cost any torque at all(other than the added mass the driveline has to turn).
For that matter, the sure grip unit actually does nothing, if the traction is the same on both wheels.
Of course there is probably some wizzy scientific explanationa as to why it is true.
Posted By: DaytonaTurbo
Re: Sure grip = 15% torque loss? - 07/15/09 04:59 AM
Well it would feel like a torq loss, you can have a car that'll spin one tire 20', then you put a suregrip on and it feels like a dog because you're actually getting some traction.
Posted By: HotRodDave
Re: Sure grip = 15% torque loss? - 07/15/09 05:09 AM
No performance improvement from open diferential, unless your car is useing the wheel slipage as a way to multiply the tq because your tq converter is too tight. There is no tq multiplying though.
Back before my car had any musterd I swapped from a 2.94 open to a 2.94 sg both 7.25s and it felt slower with the SG but ets were quite a bit better and on the street I could finally get a jump on my wife in her maxima.
Posted By: SomeCarGuy
Re: Sure grip = 15% torque loss? - 07/15/09 05:29 AM
Quote:
Sorry I don't buy it.
All a limited slip unit is, is a set of spring loaded clutches, that try to hold the side gears to the carrier.
I don't see how it could cost any torque at all(other than the added mass the driveline has to turn).
For that matter, the sure grip unit actually does nothing, if the traction is the same on both wheels.
Of course there is probably some wizzy scientific explanationa as to why it is true.
Posted By: Lefty
Re: Sure grip = 15% torque loss? - 07/15/09 06:09 AM
Quote:
the sure grips/or posi type can take up to 15% of the turning torque away.
That energy would have to go somewhere and probably make a huge amount of heat, so I say no way... 
Posted By: Charrlie_S
Re: Sure grip = 15% torque loss? - 07/15/09 02:24 PM
I don't know for sure, but I think in a straight line, with both wheels haveing traction, there would be no power/torque loss. While turning, the clutches would slip, to allow one wheel to turn faster. This would generate heat, resulting in a power/torque loss.
Come to think about it, if the clutches were doing their job as designed (to transfer power to the wheel with the most traction), there would be heat generated, and this would equate to a power loss.
Posted By: gamagoat6x6
Re: Sure grip = 15% torque loss? - 07/15/09 11:54 PM
Figure a well built 440 makes 500 foot pounds. 15% of that is 75 and there`s no way the axle is gonna create that kind of drag.
Posted By: DaytonaTurbo
Re: Sure grip = 15% torque loss? - 07/16/09 12:07 AM
Like I said, it won't create an actual torq loss, but it can feel like one if you're using that one spinning tire to get engine RPM's up if you've got a tight torq converter. If you say had a converter that flash stalls to 4000-5000, you would not notice any torq difference between the two, other than never being able to hook with that peg legger.
Posted By: CJK440
Re: Sure grip = 15% torque loss? - 07/16/09 12:23 AM
Seems to me, that there is a certain amount of drag in a limited slip when turning that is exacerbated when under power.
Posted By: 70Cuda383
Re: Sure grip = 15% torque loss? - 07/16/09 12:24 AM
only 1 way to prove it! if anyone is planning on putting an LSD into their axle, go to the dyno first, get a baseline.
then swap in the LSD and go re-dyno to see if there's a loss.
this would only work if the ONLY thing you changed was the diff, and did not do a gear change at the same time.
Posted By: Pacnorthcuda
Re: Sure grip = 15% torque loss? - 07/16/09 12:33 AM
Ever driven a live axle go-kart? Those things are dogs at low speed with the wheel cranked. Everyone guickly learns to accelerate in the straightest line possible. Reason is simple, in a turn, the engine has to not only accelerate the mass, but over come the friction of the two rear tires having to turn different speeds.
Now in a limited slip, the axle can differentiate, which GREATLY helps, but there is friction present in the cones/clutches, generating heat, all made possible from consuming torque from the motor. So yes there is some truth to it....IF (big IF) the differnetial is being forced to differentiate (its in a turn).
Straight line? I wouldn't think there would be a difference, and of course if the peg-leg set begins to spin......
...and as far as a 15% torque loss? I don't believe it.
Posted By: forphorty
Re: Sure grip = 15% torque loss? - 07/16/09 02:18 AM
i have no earthly idea. but if an open open differential requires,say, 30 lb-ft to turn, an additional 15% is only 4.5 lb-ft more. almost insignificant.
Posted By: burnt_o_matic
Re: Sure grip = 15% torque loss? - 07/16/09 02:38 AM
Quote:
up to 15% of the turning torque away
Was that a circle track racer telling you this? There may be some truth to it in that situation.
Posted By: 70Cuda383
Re: Sure grip = 15% torque loss? - 07/16/09 03:11 AM
Quote:
Quote:
up to 15% of the turning torque away
Was that a circle track racer telling you this? There may be some truth to it in that situation.
Good catch! TURNING TORQUE! yes, I'd believe it if you had full traction on both tires, in a turn, when you're now forced to slip the clutches in the LSD.
maybe this is where a detroit true trac would be beneficial? no clutches, all gear LSD...acts like an open around a turn, until you gas it, then it acts like a locker, right?
I know if I have 1 wheel up in the air, the darn thing spins around and around like an open diff! scared me the first time I did that with it installed! I didn't fully understand how it worked yet!
Posted By: MoparforLife
Re: Sure grip = 15% torque loss? - 07/16/09 11:23 AM
Quote:
Quote:
up to 15% of the turning torque away
Was that a circle track racer telling you this? There may be some truth to it in that situation.
If it was he won't have to worry about it long using a SG on the circle track. 
Posted By: CJK440
Re: Sure grip = 15% torque loss? - 07/16/09 11:47 AM
Quote:
only 1 way to prove it! if anyone is planning on putting an LSD into their axle, go to the dyno first, get a baseline.
then swap in the LSD and go re-dyno to see if there's a loss.
this would only work if the ONLY thing you changed was the diff, and did not do a gear change at the same time.
A chassis dyno simulates a straight line run. If you could find a dyno that had rollers that were different diameters I think you'd see more loss with an LS rear than an open.
Posted By: 70Cuda383
Re: Sure grip = 15% torque loss? - 07/16/09 03:26 PM
Quote:
Quote:
Quote:
up to 15% of the turning torque away
Was that a circle track racer telling you this? There may be some truth to it in that situation.
If it was he won't have to worry about it long using a SG on the circle track.
don't the nascar guys use LSDs? I've never seen one do the one tire fryer when they do their celebratory donuts at the end of the race, and theres always 2 equal, long black marks. although I've wondered that before myself--how can they use a LSD when they're making left hand turns ALL DAY
Posted By: Anonymous
Re: Sure grip = 15% torque loss? - 07/16/09 03:54 PM
IMO, having a LSD has much more benefits than it has negatives. They may take more power to make a turn but only if power is being applied and under normal cruise conditions, they are slipping pretty easily.
Posted By: MoparforLife
Re: Sure grip = 15% torque loss? - 07/16/09 04:13 PM
[quotedon't the nascar guys use LSDs? I've never seen one do the one tire fryer when they do their celebratory donuts at the end of the race, and theres always 2 equal, long black marks. although I've wondered that before myself--how can they use a LSD when they're making left hand turns ALL DAY
No they do not use a limited slip perse'. Depending on what you want to call it I guess:
"Regarding the "diff", the only style that can be run per the rules is a "detroit locker" type."
Using the Locker and tire stagger achieves the needed slippage in most cases. http://stockcarscience.com/blog/index.php/2008/04/01/p52
Posted By: 70Cuda383
Re: Sure grip = 15% torque loss? - 07/16/09 04:45 PM
so it's a true trac, gear style slip? or the ratcheting locker type that a lot of 4x4 guys use?