| t walgamuth |
12-29-2020 01:10 PM |
Any Cobras built with open diff?
Just crossed my mind.
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| Gaz64 |
12-29-2020 04:51 PM |
Good question.
But why have an open diff in such a light car, and V8 powered?
Gary
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| t walgamuth |
12-29-2020 05:54 PM |
Its a lot safer when you step on the gas, or just let off abruptly.
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| patrickt |
12-29-2020 06:58 PM |
Quote:
Originally Posted by t walgamuth
(Post 1487075)
Its a lot safer when you step on the gas, or just let off abruptly.
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I think more guys have gotten in trouble with a Cobra when they don't have a limited slip. An open differential sends more power to the wheel with the least amount of resistance. So what happens is that when you have a loss of traction during hard acceleration, and then it comes back (maybe you hit a little sand on the road), it's way easier to lose control. |
| t walgamuth |
12-29-2020 09:04 PM |
I disagree. The open diff allows one side to always have traction for stability in a straight line.
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| Snake2998 |
12-30-2020 12:56 AM |
Quote:
Originally Posted by t walgamuth
(Post 1487086)
I disagree. The open diff allows one side to always have traction for stability in a straight line.
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That's how I see it as well. I think the non-driven wheel maintains straight line traction reducing (not negating) the tendency for the tail to slide out. I have an open 3.08 diff with TH400 box and at the time Bridgestone no traction tyres by the way and have found it to be very little disadvantage on the drag-strip - in 1993 with the original very mild 350 motor managed an easy 13.5 second 1/4 mile beating many potentially faster Cobras (their were 20 Cobras on the day) with open and closed diffs mainly because I could keep on it right from the start whilst they were smoking and sliding their way behind me - I was second fastest on the day being thoroughly beaten by a highly tuned 383 with a driver who knew what he was doing and who achieved 12.5 seconds. At the time most of the Cobras were running Bridgestones as they were the only tyres available in suitable sizes in South Africa. |
| FredG |
12-30-2020 07:42 AM |
Rear
My original plan was to order a car brand new and I do recall specifically one dealer discouraging my wanting an LSD or posi rear and citing the safety of having one tire fixed as opposed to both spinning at the same time. The car I purchased has an LSD. I now can see his point.
Fred
Quote:
Originally Posted by t walgamuth
(Post 1487086)
I disagree. The open diff allows one side to always have traction for stability in a straight line.
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| joyridin' |
12-30-2020 08:07 AM |
I think BDR was one Cobra Mfg. that used BMW rear differentials that were not LSD. I recall reading a few postings on here asking what they would need to do.
Probably the best set-up is a torsen style differential. It will allow you to smoke both tires if you desire and won't put you facing traffic on a damp street.
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| patrickt |
12-30-2020 08:10 AM |
Alright, I see your argument on the safety aspect. Here's a pretty decent article that cites some of your points: https://drivetribe.com/p/how-limited...SmyQxXCdjAM4Pw From a performance perspective though, a LSD car is always going to be faster than an open diff car, particularly in and through the corners. But, if you look at an open diff as kind of a "rev limiter" for the performance of the car, then you have a point. And, considering that most of us here are not Stirling Moss, than can certainly be a good thing.:cool: |
| t walgamuth |
12-30-2020 09:30 AM |
I will agree that I am no Stirling Moss.
I have a Formula Ford (F) which I autocross vigorously. I also have the Orange VSE which I autocrossed vigorously. I find the FF to be much more forgiving than the Cobra. I first thought it was just a better chassis but after more thought decided it was because the FF has an open diff. You'd never notice it by driving it or at least I did not. The Cobra if you come off the gas abruptly with the light weight and limited slip the rear end will come right on around just as if you were applying rear brakes only.
The Lotus 7 replica DM car which I autocrossed before the Cobra has a limited slip too and under certain conditions would lose the rear end and no matter what I did after that could not catch it. The trick is to left foot brake and keep your right foot down some on the gas while applying the brakes.
The limited slip has been no problem in either car on straightaways.
Of course the limited slip enhances the "Butch" factor.;)
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| FredG |
12-30-2020 11:30 AM |
Sterling Moss
As we all can attest to. Chit happens fast and can quickly turn to "oh chit" in these cars.
Fred
Quote:
Originally Posted by t walgamuth
(Post 1487109)
I will agree that I am no Stirling Moss.
I have a Formula Ford (F) which I autocross vigorously. I also have the Orange VSE which I autocrossed vigorously. I find the FF to be much more forgiving than the Cobra. I first thought it was just a better chassis but after more thought decided it was because the FF has an open diff. You'd never notice it by driving it or at least I did not. The Cobra if you come off the gas abruptly with the light weight and limited slip the rear end will come right on around just as if you were applying rear brakes only.
The Lotus 7 replica DM car which I autocrossed before the Cobra has a limited slip too and under certain conditions would lose the rear end and no matter what I did after that could not catch it. The trick is to left foot brake and keep your right foot down some on the gas while applying the brakes.
The limited slip has been no problem in either car on straightaways.
Of course the limited slip enhances the "Butch" factor.;)
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| patrickt |
12-30-2020 11:47 AM |
Quote:
Originally Posted by patrickt
(Post 1487105)
... a LSD car is always going to be faster than an open diff car, particularly in and through the corners.
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Well, maybe a pro can comment on this statement instead of just taking my word for it. If I don't have to make it out of the corner, I can fly in to the corner as fast as any pro can. Maybe faster.:cool: |
| t walgamuth |
12-30-2020 11:55 AM |
Mark Donahue used to say if you don't like a locked rear end you aren't going fast enough
(or something like that);)
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| FredG |
12-30-2020 01:21 PM |
Open vs Posi
Growing up in the era of the muscle cars, no self respecting muscle car owner wanted an open rear or let it be known he had one. They were referred to as one wheel peelers. It was full posi or nothing. The LSD has certainly changed the game for traction. For a 100% wheel grabbing launch off a starting line it was full posi. All cars got squirrely. Good drivers, tuned suspensions and suitable tires kept the car straight. I imagine going around a corner in a 2400lb car would be a bit more challenging.
Fred
Quote:
Originally Posted by patrickt
(Post 1487117)
Well, maybe a pro can comment on this statement instead of just taking my word for it. If I don't have to make it out of the corner, I can fly in to the corner as fast as any pro can. Maybe faster.:cool:
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| cycleguy55 |
12-30-2020 01:31 PM |
Having one rear tire spinning madly while the other maintains directional stability will provide a 'safer' experience - arguably better for people less inclined to effectively moderate the 'loud pedal'.
Any kind of functional limited slip mechanism will be faster than an open differential in a straight line or road course at the hands (and feet) of someone who knows what they're doing behind the wheel. It could also be a disaster for someone who fails to exercise restraint and discovers how quickly the arse end wants to 'step out' through injudicious applications of throttle (on or off).
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| t walgamuth |
12-30-2020 02:51 PM |
Exactly.
I have never let anybody drive it since I have owned it. I've never been sideways in it on the street but have spun it out a few times autocrossing.
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| 6TNCRZY |
12-30-2020 03:15 PM |
A limited slip is probably the easiest to drive as there is some "slip" in corners. A Detroit Locker or Truetrack can be fun to drive and aid corner entry, but can be tricky because when they engage both rear wheels are locked at the same speed.
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| eschaider |
12-30-2020 05:19 PM |
Yes on the locker and no on the Trutrac. TruTrac is Torque Biasing diff and directs the torque proportionally to the tire with the greater traction. It also drives the inner and outer wheels at different speeds in turns. The Torque Biasing diff's claim to fame is that they are totally smooth, do not bind, vibrate, or chatter at all on tight turns in high or low traction situations. Very nice design originally invented for F-1 cars in the 1960's
To learn more click here => Torque Biasing Diffs
Ed |
| Morris |
12-30-2020 07:00 PM |
I’ve used many different Differentials over the course of time......the welded up diff was great for autocross.....the limited slip requires a lot of maintenance to keep it working properly......the Salisbury Diff was the same way but the ramps not the diff allowed you the control how much drive you got on both rear tires.....and finally we are using the Quaiffe diff in the KMP259 and it works the best as it allows the rear wheels to unlock and turn in at the appropriate moment.....then as you accelerate towards the apex, the rear wheel drive the vehicle but not so much to push you away from the apex.....by the time you push the throttle down to the floor the Quaiffe diff locks up and drives the vehicle past the apex to the exit of the turn.......even in a straight line the car will jump a bit to one side or another....but then it catches and pulls straight forward......it is better to drive smoothly around the corners......and the Quaiffe verses the open, Welded, LSD, or Salisbury is by far better then the others.
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| t walgamuth |
12-30-2020 07:16 PM |
I had a welded diff on one of my old autocross cars for a while. It would push the front like crazy on a slow turn.
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