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-   -   Differential Strength (http://www.clubcobra.com/forums/backdraft-racing/137410-differential-strength.html)

bobcowan 10-22-2016 09:13 AM
Differential Strength
 
For my third Cobra, I'm taking a serious look at Backdraft. I have about a million questions.

1. How strong are the diff and axles? How much power can you put through it and still maintain reliability?

2. Can the chassis accept a 460 Lima motor without mods?

Cashburn 10-22-2016 03:20 PM
Quote:
Originally Posted by bobcowan (Post 1406878)
For my third Cobra, I'm taking a serious look at Backdraft. I have about a million questions.

1. How strong are the diff and axles? How much power can you put through it and still maintain reliability?

2. Can the chassis accept a 460 Lima motor without mods?
To the best of my knowledge, and based on watching this forum for 14 years or so, I am only aware of one differential breaking and I believe it was on the track. I should say I'm aware of 2, the other did not have oil in it. We have put 900hp through them with some simple modifications. The standard setup from the factory is good for under 600hp.

Yes a 460 will fit and we have headers available. We did opt to make our own larger primary headers for a Roush 588 install.

blykins 10-22-2016 05:16 PM
Gary Bowman broke the rearend in his BDR. He was out on the street, but if I remember right, it was under a huge traction loss and then suddenly hooked up. That engine was around 650 hp if I remember correctly.

So where's the other 999,998 questions? :D

bobcowan 10-22-2016 05:46 PM
Quote:
Originally Posted by Cashburn (Post 1406902)
To the best of my knowledge, and based on watching this forum for 14 years or so, I am only aware of one differential breaking and I believe it was on the track. I should say I'm aware of 2, the other did not have oil in it. We have put 900hp through them with some simple modifications. The standard setup from the factory is good for under 600hp.

Yes a 460 will fit and we have headers available. We did opt to make our own larger primary headers for a Roush 588 install.
What simple mods did you make. My last car was making a little more than 500 on the chassis dyno. I'd like to do better this time. And I don't exactly drive it easy. Donuts make me laugh out loud. :)

Quote:
Originally Posted by blykins (Post 1406912)
Gary Bowman broke the rearend in his BDR. He was out on the street, but if I remember right, it was under a huge traction loss and then suddenly hooked up. That engine was around 650 hp if I remember correctly.

So where's the other 999,998 questions? :D
Coming, be patient. ;)

Jus Cruisin 11-04-2016 06:55 PM
Non owner here wondering about the standard rearend. Frank assures me there is little need for the limited slip on the street. I guess go with it and swap it out down the road., I just don't like the idea of "peg leg" burnouts that might occasionally happen. What are the thoughts from owners? Thanks!

Cashburn 11-04-2016 08:38 PM
Quote:
Originally Posted by blykins (Post 1406912)
Gary Bowman broke the rearend in his BDR. He was out on the street, but if I remember right, it was under a huge traction loss and then suddenly hooked up. That engine was around 650 hp if I remember correctly.

So where's the other 999,998 questions? :D
I thought he broke it due to a loose bolt? But I don't know for sure. I'll dig up dyno info...

Cashburn 11-04-2016 08:58 PM
Quote:
Originally Posted by bobcowan (Post 1406916)
What simple mods did you make. My last car was making a little more than 500 on the chassis dyno. I'd like to do better this time. And I don't exactly drive it easy. Donuts make me laugh out loud. :)



Coming, be patient. ;)
Just saw this. If I forget to reply tomorrow just email me.

Bill Bulmer 11-04-2016 09:24 PM
I just changed from the 3.46 factory open differential to a 3.91 posi, and it is like a different car. All the chugging and bucking from lagging at low rpm's is gone, and I can actually get decent traction when I hit he gas in 1st and 2nd now. I would order the car with the posi if I had it to do again.

mln385 11-05-2016 05:25 AM
Quote:
Originally Posted by Jus Cruisin (Post 1407926)
Non owner here wondering about the standard rearend. Frank assures me there is little need for the limited slip on the street. I guess go with it and swap it out down the road., I just don't like the idea of "peg leg" burnouts that might occasionally happen. What are the thoughts from owners? Thanks!
My opinion is the car is safer to drive the rear stays put and does not want to come around as easy. Ordered mine with the LSD .

genolan 11-05-2016 05:32 AM
Is an E36 M3 LSD a direct swap on a RT2 car? 4 Bolt drive shaft?

Millsy 11-05-2016 05:47 AM
If you are going to have n engine put in with high H.P., say over 400 H.P. then i would suggest LSD. I went with a 525 H.P. motor and we decided the posi LSD was the way to go. My backdraft car is still being built but I have found the cars i have driven with LSD are more controllable when putting down alot of power to the ground. JMO

Jus Cruisin 11-05-2016 06:09 AM
Quote:
Originally Posted by Bill Bulmer (Post 1407944)
I just changed from the 3.46 factory open differential to a 3.91 posi, and it is like a different car. All the chugging and bucking from lagging at low rpm's is gone, and I can actually get decent traction when I hit he gas in 1st and 2nd now. I would order the car with the posi if I had it to do again.
What kind of rpm are you seeing at 70 mph in 5th gear with the 3.91?

bobcowan 11-05-2016 09:24 AM
I think a car like this without some kind of limited slip is silly. Gotta have it. They're so light, and any amount of power can easily beak the tires free. Esepcially if traction is a little bit limited.

Clutch types work pretty well, but can sometimes cause a push on corner exit. On the street that's not a big issue.

If I was going to be racing, I'd order the standard diff and save the $2,100. Then swap it out for a worm gear, like TruTrak or Torsen. About the same money, but more geared towards racing.

Jus Cruisin 11-05-2016 11:26 AM
I'm sticking with the stock rearend for the build. I'll track down a used lsd rearend at a recycle yard or off eBay. More cost effective.

Cashburn 11-05-2016 01:06 PM
Quote:
Originally Posted by bobcowan (Post 1407968)
If I was going to be racing, I'd order the standard diff and save the $2,100. Then swap it out for a worm gear, like TruTrak or Torsen. About the same money, but more geared towards racing.
For E36 Diff?

Cashburn 11-05-2016 01:14 PM
Quote:
Originally Posted by blykins (Post 1406912)
Gary Bowman broke the rearend in his BDR. He was out on the street, but if I remember right, it was under a huge traction loss and then suddenly hooked up. That engine was around 650 hp if I remember correctly.

So where's the other 999,998 questions? :D
I don't have the timeline exactly. Not sure if these numbers were before delivery or when it came back because he had pulled the engine and redone something.

Run 3 it was: 535RWHP / 461.64T
Run 9 it was: 548.53RWHP / 485.95T

Bill Bulmer 11-05-2016 03:43 PM
I am at 2200 RPM at 70 mph with the 3.91 rear end and the T-5 transmission (I just re calibrated the speedometer).

blykins 11-05-2016 03:46 PM
http://www.clubcobra.com/forums/back...oken-diff.html

http://www.clubcobra.com/forums/smal...g-block-2.html

Grey 65 11-05-2016 05:24 PM
[quote=blykins;1407989]http://www.clubcobra.com/forums/back...oken-diff.html

Not a broken diff. someone did NOT tighten 6 bolts correctly and the half shaft came loose and hit the diff cover cracking the diff cover...

Kevin....

Mother 11-12-2016 06:32 AM
I have been using a 1971 Ford Torino 9 inch for many years. The 3.46 ratio with an Auburn ratchet spool has never given up. I check the lash every second year just to be safe. My engine produces 740/ 680 at the finals. No problems.


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