PDA

View Full Version : Having trouble building a period-correct '97 Cobra TA tune



r4y30n
04-03-2018, 18:19
So the other night I ran a few laps in the Trans/Am Cobra and decided to try a period-correct setup with the Detroit Locker-style ratcheting diff swapped into the SMS stable tune, wow that became a mess quick! On fast tracks it's not too bad when it's locked under power but turn in after braking whips the car around into a spin before I can blink. Anyone here know how the guys set up their cars back then to deal with this? Or am I just not skilled enough to catch it before it spins?

blinkngone
05-03-2018, 02:32
So the other night I ran a few laps in the Trans/Am Cobra and decided to try a period-correct setup with the Detroit Locker-style ratcheting diff swapped into the SMS stable tune, wow that became a mess quick! On fast tracks it's not too bad when it's locked under power but turn in after braking whips the car around into a spin before I can blink. Anyone here know how the guys set up their cars back then to deal with this? Or am I just not skilled enough to catch it before it spins?

The reason you are not getting responses is that the Default LSD for this car is a Clutch LSD. To get the car to turn with your LSD you have to set the car up loose and power the rear end into a slide and try to catch it as you are already attempting.
The rear damper Slow bump is at 4400 so you could try going way up an see if you can get it to slide with the least amount of power applied. You are a pioneer.
251163
Meh, nevermind, it slides to easy.

blinkngone
05-03-2018, 03:29
Ok, I managed to beat a Default setup at Silverstone National with your ratchet LSD. I have one arm and my legs don't work much but it is possible. What time have you run in TT at Silverstone National? I used to run 52s with this car in PC1 at this track. So I am now 5 seconds slower but it could be a combination of the ratchet and my reduced abilities.
251166

Jussi Karjalainen
05-03-2018, 12:57
The single biggest thing you should change when swapping over to a ratcheting diff is engine braking. With no deceleration locking to help you, engine braking is your worst enemy. The default engine braking compensation setting on the stable setup is 3, for ratcheting I'd recommend 12 as a starting point (higher than that car start causing some run-away throttle issues).

After that the next biggest thing is driving style: Brake in a straight line, always keep some pressure on the throttle when turning, even during entry. Only if you specifically need to tuck in tighter do you lift the throttle, and even then avoid lifting it completely. And since you have almost no engine braking at this point, you can move the brake bias towards the rear. Testing at Road America I got a pretty good starting point by taking the Loose setup, switching to the ratcheting diff, increasing engine braking compensation to 12 and setting brake bias to 52/48 and pressure to 88%.

Ratcheting diffs aren't great for racing. It was said by many to be the worst possible diff for racing, after the completely open diff (all the downsides of the ratcheting but you can't put power down as well).

blinkngone
05-03-2018, 13:28
Yeah, I can't manipulate the throttle very well anymore but I am trying to feather it through corner entry and exit. Still I am slower than I would like. I am also not braking very well which makes throttle control more difficult. Ran a 0:57.255 which is better but I need to make up seconds. I can only do 1 lap at a time so the tires are messing up being not stable or up to pressure and temperature.

blinkngone
05-03-2018, 17:02
So the other night I ran a few laps in the Trans/Am Cobra and decided to try a period-correct setup with the Detroit Locker-style ratcheting diff swapped into the SMS stable tune, wow that became a mess quick! On fast tracks it's not too bad when it's locked under power but turn in after braking whips the car around into a spin before I can blink. Anyone here know how the guys set up their cars back then to deal with this? Or am I just not skilled enough to catch it before it spins?

Hi, would you mind running your ratchet at Silverstone National TT so I have something to shoot for? Don't know if I can help you out much but I can try.

cpcdem
05-03-2018, 19:30
Hi, would you mind running your ratchet at Silverstone National TT so I have something to shoot for? Don't know if I can help you out much but I can try.

Blink, I'd be happy to give some help and register a time myself as well. Should I be using the setup from your TT lap, does this one have the diff setup as you want it? (I'm really clueless about diff terminology, only thing I know is how to adjust my standard angles/preload diff :))

blinkngone
05-03-2018, 21:27
Blink, I'd be happy to give some help and register a time myself as well. Should I be using the setup from your TT lap, does this one have the diff setup as you want it? (I'm really clueless about diff terminology, only thing I know is how to adjust my standard angles/preload diff :))
Thanks! Yes mine has Jussi's recommendations as well as the ratchet. Appreciate it!

blinkngone
05-03-2018, 22:03
Oh, cpcdem could you run a Default Loose setup before you go to the ratchet so we have a guidepost?

cpcdem
05-03-2018, 23:18
I just did a lap with your setup, wow that was interesting, plenty lift off oversteer! There's more time available, as you will see I made a couple mistakes, if you want me to do a better lap, please tell me!

About comparing setups, I did much practice in Algarve with the same car on default, will now try some laps with your special setup as well and will compare (will just put the radiator back to 75% to make the comparison fair).

blinkngone
05-03-2018, 23:43
I just did a lap with your setup, wow that was interesting, plenty lift off oversteer! There's more time available, as you will see I made a couple mistakes, if you want me to do a better lap, please tell me!

About comparing setups, I did much practice in Algarve with the same car on default, will now try some laps with your special setup as well and will compare (will just put the radiator back to 75% to make the comparison fair).
Thanks! Hopefully the OP can make a run and we can start comparing notes. This is a real challenge, I am pretty sure that with a Clutch LSD the Cobra is a low 54s car. I think Jussi mentioned you can't really lift so maybe when you get some practice and give it another try you will be better. I'll try following your ghost.

cpcdem
05-03-2018, 23:54
Thanks! Hopefully the OP can make a run and we can start comparing notes. This is a real challenge, I am pretty sure that with a Clutch LSD the Cobra is a low 54s car. I think Jussi mentioned you can't really lift so maybe when you get some practice and give it another try you will be better. I'll try following your ghost.

Yeah, there's definitely a lot more time to gain, I just left that run there with the mistakes, until you tell me to do a faster one.

I tried your setup in Algarve though, and (even though I did not log it), I was doing a lap around half a second faster than default. I think the extra time was due to being able to go on throttle much sooner on corner exit or while cornering. I also tried to use again default and only enable ratcheting (and siable the others), wow that lift off oversteer was massive! But increasing engine braking as in your setup and as Jussi suggested, did make it a lot better indeed.

blinkngone
05-03-2018, 23:55
Ok, cpcdem I just ran your ghost and that really helped! I expect you can get into the low 55s when/if you try again.
251217

cpcdem
06-03-2018, 00:17
Ok, cpcdem I just ran your ghost and that really helped! I expect you can get into the low 55s when/if you try again.


Done, a 55.4. I actually also did a lap almost one second faster, but got invalidated. I really like this throttle using for car steering in low speed, similar to the touring cars that i am racing a lot lately, but it's very easy to get it wrong when you try to drive on the limit :)

blinkngone
06-03-2018, 00:28
Done, a 55.4. I actually also did a lap almost one second faster, but got invalidated. I really like this throttle using for car steering in low speed, similar to the touring cars that i am racing a lot lately, but it's very easy to get it wrong when you try to drive on the limit :)
Cool! Thanks! I think we have enough for the OP's needs. So, worst case he is possibly only a second slower than the Clutch LSD meaning he could compete with many drivers using his ratchet.:cool:
Nice working with you again!

cpcdem
06-03-2018, 01:52
Cool! Thanks! I think we have enough for the OP's needs. So, worst case he is possibly only a second slower than the Clutch LSD meaning he could compete with many drivers using his ratchet.:cool:
Nice working with you again!

Yeah, with you too, remembering the old times :)
Btw, after using the engine braking workaround, I think that ratchet thing is a bit faster than default diff, since it allows putting power on more quickly. Still needs to be careful when off throttle though.

blinkngone
06-03-2018, 02:39
Yeah, he won't be running against Default setups though if he's racing but he should be close.

blinkngone
06-03-2018, 03:01
Hi cpcdem. How about you try the ratchet with a car you are more familiar with like one of your touring cars and see what you think?

cpcdem
06-03-2018, 04:16
Hi cpcdem. How about you try the ratchet with a car you are more familiar with like one of your touring cars and see what you think?

Good idea, had not realized this option is available in all cars, thought it was specific to that Cobra one. It's too late now, but will try that tomorrow.

blinkngone
06-03-2018, 12:50
I tried the 320 TC, the 320 Turbo the 69 Camaro and others. I couldn't do much with the ratchet, it was too difficult for me, I think I may have lost 1 of my 9 lives trying.:eek:
I was able to tiptoe around with the Marek LMP2, it has no available Engine Braking.
251248

cpcdem
09-03-2018, 18:21
Hi cpcdem. How about you try the ratchet with a car you are more familiar with like one of your touring cars and see what you think?

I tried with a few (BMW TC, GT3s) and realized why they do not make cars like that now :)
That snap oversteer is very hard to deal while decreasing engine braking helps, it's still too hard for me.

Maybe there are other cars that could benefit from it, as it is helpful for the Cobra when going on gas during corners. But then again, guess it's much easier (and better) to simply tune the normal diff to achieve the same benefit, without the disadvantages of the ratchet diff.

blinkngone
09-03-2018, 18:42
I tried with a few (BMW TC, GT3s) and realized why they do not make cars like that now :)
That snap oversteer is very hard to deal while decreasing engine braking helps, it's still too hard for me.

Maybe there are other cars that could benefit from it, as it is helpful for the Cobra when going on gas during corners. But then again, guess it's much easier (and better) to simply tune the normal diff to achieve the same benefit, without the disadvantages of the ratchet diff.

Thanks, I feel the same. I think I might try the Zakspeed Capri just for laughs. Oops, nevermind Ho Ho Ho.

Jussi Karjalainen
09-03-2018, 19:27
The ratcheting diff really wasn't a good idea for racing ever, it's only really useful for road traffic where you don't really need decel locking (cars are designed with mostly open differentials anyway, and you want to be able to maneuver the car as well as possible, but the on power locking helps with traction when it's slippery out there). Compared to a spool, only a racing car that specifically had issues turning into a corner would benefit from it, and at that point you'd be better off with a normal diff. Maybe in the early days (50s and 60s) when they hadn't really figured out reliable LSDs that well you could have seen it as a useful thing, as they were quite reliable, but the order of preference really is LSD (clutch/torsen/viscous/electronic/etc.) > Spool > Ratcheting > Open.

The only reason to run a ratcheting diff in the 90s was being forced to do so by the regulations, just like the only reason to run a spool these days (outside of drag racing) is being forced to do so by the regulations. Some series consider it a part of the formula, like NASCAR and V8 Supercars. =)

On a general level at least.

One car that springs to mind that might work decently on a ratchet is the 917/10. That thing has pretty severe turn-in problems on the spool it's usually running (Porsche primarily used spools in all of their cars in the 70s and 80s, 935s, 936s, 956s, 962Cs, etc. because their engines had a habbit of destroying LSDs of the time).

blinkngone
09-03-2018, 19:47
The ratcheting diff really wasn't a good idea for racing ever, it's only really useful for road traffic where you don't really need decel locking (cars are designed with mostly open differentials anyway, and you want to be able to maneuver the car as well as possible, but the on power locking helps with traction when it's slippery out there). Compared to a spool, only a racing car that specifically had issues turning into a corner would benefit from it, and at that point you'd be better off with a normal diff. Maybe in the early days (50s and 60s) when they hadn't really figured out reliable LSDs that well you could have seen it as a useful thing, as they were quite reliable, but the order of preference really is LSD (clutch/torsen/viscous/electronic/etc.) > Spool > Ratcheting > Open. The only reason to run a ratcheting diff in the 90s was being forced to do so by the regulations, just like the only reason to run a spool these days (outside of drag racing) is being forced to do so by the regulations. Some series consider it a part of the formula, like NASCAR and V8 Supercars. =)



On a general level at least.

One car that springs to mind that might work decently on a ratchet is the 917/10. That thing has pretty severe turn-in problems on the spool it's usually running (Porsche primarily used spools in all of their cars in the 70s and 80s, 935s, 936s, 956s, 962Cs, etc. because their engines had a habbit of destroying LSDs of the time).

Ok, I'll give it a shot with the 1200 hp 10.:D Well, that was interesting. It's really difficult to control on boost, I can lose it shifting gears(using automatic) in a straight line. It spins much easier than the Cobra on corner entry.

cpcdem
09-03-2018, 22:22
Ah, right, regulations! That's a good enough reason to use it indeed :)

r4y30n
11-03-2018, 01:07
Wow, I didn't expect this thread to prompt such a discussion!

I finally got some time to fiddle around with this a bit more... Ran a few laps today at Silverstone National in the default loose setup then I swapped the diff to ratcheting and set engine braking to 10 and actually went .5 sec quicker! Engine braking must have been the major culprit in my early attempts, previously I had it set to 0 and every time I lifted off the throttle the braking torque would hit one wheel or the other and abruptly start turning the car (seems obvious in hindsight). It was difficult enough just trying to drive straight out of the pit lane onto the track and was really unpredictable under braking.

Thanks for all the input everyone! Now I really feel like I've gone back in time 20 years when driving this thing.