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fakesnake
05-01-02, 07:32 PM
Hiya Boys and Girls,

Me and Dad have just picked up our doner kit from Pilgrim and have a DIFFicult choice (ha ha ha). We have can use either the standard Granada Diff or a LSD from a Sierra XR4x4 we have.

We are worried that the Sierra diff wont cope with the 250bhp our engine will make. The Granny diff has a larger casing but the distance between the drive takeoffs are the same. Obviously we would like to use the LSD but dont want it blowing up. Will The XR4x4 dif cope with 250bhp?

Thanks all...

Chris }>

James
05-01-02, 07:58 PM
Hi

What engine will you be running

Regards

James:) :)

fakesnake
06-01-02, 11:36 AM
Its a Rover V8. Heres the spec:

4.0 Litre V8
9.75:1 compression ratio
500 Weber on Edelbrook manifold
Stage 2 Heads
Custom ground fast road cam by DJE

Should be 240 - 260 bhp (hopeing for the 2nd figure ;-) )

Chris }>

agwebsites
07-01-02, 12:09 PM
Quick answer is that as long as the 4x4 LSD is in good condition it should hold.

You would be using a dif that has been designed to run with an engine producing less BHP and Torque than your V8 and therefore you would be running it on the limit, especially if you drive it hard.

Other options you may want to consider for a more reliable and ‘safer’ drive are,

a) The dif from and Sierra Cosworth, this will hold no problem. However, it is important to get a good one as so often these cars have had a history that would make you cringe, even before someone raped it around a lamppost. A recon from a known dealer or a new one would be the safest option.

b) The LSD from a Ford Scorpio 2.9, bigger and heavier than the Sierra one. :(

c) Quaife make a stronger and improved dif with A.T.B for the Sierra :9 , which is the best option and doesn’t cost the earth. I believe AP also do one but I don’t know anything about it or anyone with one to make a comment on it.

Good luck with it all and contact me if I can be of any more help,
Andy

normanh
07-01-02, 04:33 PM
Just a thought......

Another point to remember is Your Cobra doesnt wiegh as much as the fords, so the force against your torque will be less also surely?????

The 4x4 diff was designed to cope with around 240BHP according to a very nice xmas pressie I got!! :)

NuttyNorm

agwebsites
07-01-02, 04:54 PM
"Another point to remember is Your Cobra doesnt wiegh as much as the fords, so the force against your torque will be less also surely?????"

Which means your back wheels should start wheel spinning before the diff goes pop and thus should hold back your 250BHP.

normanh
07-01-02, 05:35 PM
diff going pop....not exactly, maybe I'm not putting this right or maybe its totally wrong..

The diff transfers the energy to act against the cars weight no? in order to make it move. So resistance thru the diff is from the weight of the car. If this resistance was too high (car too heavy) the diff wouldn't last five minutes surely?

The sierra diff was designed to cope with a certain amount of power against a certain weight... now if that weight is reduced surely the resisting force is lower? and then it follows the amount of power the diff could handle goes up?

I think this is a facinating point that leads me to think this.... Pilgrim run 220Bhp thru a standard 2ltr diff. Now a 2ltr only produces 105bhp if your lucky, so how comes the diffs dont give up....1/2 the wieght I thought.

So am I completely wrong in my thinking?

NuttyNorm.

Brain back in box ready for repair....or not?! :+

fakesnake
07-01-02, 05:50 PM
Well...

I popped out to our garage too look at our bigger Granny diff. I thought to myself i'll see how easily this big granny diff turns. Turned it - turned fine. But hang on! When you turn the input shaft, a normal diff's drive take offs turn different ways - but these were turning the same way. Hmmm. Using my amazing 17 years of knowledge that means its a Limited slip diff! And it must be one from a 2.9 scorpio! YEAY :) Don't thinks the guys at Pilgrim knew what they were giving us in out doner kit. Anyone wanna buy a XR4x4 LSD?

Chris }>

dave
07-01-02, 06:10 PM
I think the trick is to turn one of the output shafts,if the other one turns the opposite way it isn't a slippy. ;-)

PeteV
08-01-02, 08:37 AM
Nope !

Sorry Norm.. Torque is Torque is Torque ! - If you apply a given torque to any object then it will accelerate at a rate directly proportional to its mass. So, make it lighter and apply the same torque and you simply accelerate it faster !. That is, with your lighter car (Cobra) , youre applying the same torque exactly as if your engine and drivetrain was fitted to a Sierra, but the difference is that it accelerates you a heck of a lot quicker !

As for the strength of diffs etc., the possible shock-loading of transmission components from such things as dumping the Clutch at high revs could easily result in a peak torque many times the nett torque of the engine. If the drivetrain design didn't take this into account then I dont believe things wouldn't last literally five minutes ! So , not too many racing starts, and you should still be OK with fairly basic components & a reasonably meaty engine !

Pete.

agwebsites
08-01-02, 10:49 AM
Force on the diff is exerted from three directions,
A force pushing the car backwards when you try to move forwards from the air presser around the car,
The force pulling the car into the ground, thanks to gravity, increasing grip from the rear wheels, and,
The rotational force exerted on the dif by the propshaft.

Thus, if the force exerted by the engine is less than the eternal forces exerted on the car it won’t be able to move forwards and the energy generated will build up in the components between the different forces. Gearbox, diff, drive shafts etc. In theory if there where no external forces on the car and components it would be possible to use a plastic straw as a propshaft and Lego gears in your diff and they would hold as much power as you wanted.

So basically Norman is right, but he is right because the back wheels will not have the presser placed on them that the Sierra would and are more likely to spin giving the release of energy build up on the components.

Another point to consider though is that when you pull away in a car the front lifts up increasing the presser on the back wheels, the more powerful the engine the more the car lifts at the front and more downward presser is applied on the back wheels reducing their ability to spin.

Luckily changing the diff on my Cobra is a very easy job, so it is something I am not too worried about. :7

Cheers
Andy.