Short/Bumpy track spring rates?
04-27-2012, 12:26 PM
#16
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Yes, agree with JR, move to 125 or even 150 psi in the fronts...
04-27-2012, 01:07 PM
#17
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I'll give it a try! Also might drop a little more spring out of the front to help with the understeer there if that doesn't work. Ugh, diff diff diff... Weighing on my mind lol
04-29-2012, 04:39 PM
#19
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Wish Matt would chime in but the short answer is no. It needs to be out of the tranny and in a vise to eliminate all the variables. Do you know if the discs have ever been changed and if not how many klicks on the odometer and how many have you put on it?...
05-01-2012, 02:13 PM
#21
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I would think diff check is valid in car... only real resistance you'd have would be brake pads and ya could take those out. Only guessing, but shouldn't take much force to overcome force of spinning axle that's not straight, wheel bearing, and stub axle seal. would want to do on center nut to get most accurate result.
05-04-2012, 06:38 PM
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As others suggest, it is likely not the springs that are the primary contributor. GTC4 and 5 cars run 1480lbs/in springs at Sebring, and they are VERY quick. That's not suggesting it is ideal, but all tires have a usable range of spring rates, and going below that at any track is detrimental.
05-04-2012, 08:22 PM
#24
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As others suggest, it is likely not the springs that are the primary contributor. GTC4 and 5 cars run 1480lbs/in springs at Sebring, and they are VERY quick. That's not suggesting it is ideal, but all tires have a usable range of spring rates, and going below that at any track is detrimental.
05-04-2012, 08:30 PM
#25
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If this attached chart is correct your 142 NM equates to 105 ft.lbs. of torque which is huge. Sure you don't have a new diff with 80% lockup on acel? Just joking, well kinda of. That just doesn't figure, I'm going to ask Matt at Guard to comment.......
05-04-2012, 10:14 PM
#26
Pro
If it helps any GT3CC Australia lists this:
http://www.camsmanual.com.au/sportre...TechRegs-2.pdf
T5.3 Power Transmission/Differential
For GT3 Cup automobiles, the ramp angle of the differential lock is 32 degrees ± 17’ (acceleration) and 45 degrees ± 17’ (deceleration). The ramp angles are determined relative to the rotary axis. The resulting locking ratio in combination with the friction discs is 40/60%. The minimum locking torque of the differential is reached whenever the torque value is 80 Nm – measured at the gearbox side driveshaft flange. Falling short of the minimum value is not permissible at any time during the event. The maximum locking torque of the differential is reached whenever the torque value is 180Nm – measured at the gearbox side driveshaft flange. Exceeding the maximum value is not permissible at any time during the event.
For GT3 Cup automobiles, the ramp angle of the differential lock is 32 degrees ± 17’ (acceleration) and 45 degrees ± 17’ (deceleration). The ramp angles are determined relative to the rotary axis. The resulting locking ratio in combination with the friction discs is 40/60%. The minimum locking torque of the differential is reached whenever the torque value is 80 Nm – measured at the gearbox side driveshaft flange. Falling short of the minimum value is not permissible at any time during the event. The maximum locking torque of the differential is reached whenever the torque value is 180Nm – measured at the gearbox side driveshaft flange. Exceeding the maximum value is not permissible at any time during the event.
05-05-2012, 12:08 AM
#27
What settings are shocks at, what are you running for rebound and bump (both high and low speed), and have you tried reducing? I'm guessing the purpoising is from your low-speed, so don't reduce that too much, but the big advantage of 3-way versus 2-way is separate high and low speed bump, so take advantage of it.
What are the two ends of the car doing laterally? You're running your bars fairly soft.
I was never allowed to touch springs (spec series), so had to do all adjustments with shocks (stock Sachs two-ways) and bars, and was able to be competitive on a very wide range of tracks.
You say it's very stiff, but does that mean that you're breaking loose in the back when trying to get power down? Ie. what's the car's behavior (esp. at front and rear) going into, mid, and exiting the various corners? I don't know who your competitors were, but you've got a pretty stiffly sprung car. That's not necessarily a bad thing. Other than being hard on your kidneys (perhaps some extra seat padding?), how is it adversely affecting the car?
You say you're being outcornered because it won't set, I'm not sure I understand what that means exactly. You're not getting grip on the front end on corner entry and it's understeering on turnin and from turnin to apex? That could be your rear bar, and/or driving (the 996 Cup likes to be trail braked pretty aggressively to help rotate it).
See in a later post (this page) you mention understeer. Where exactly in the corner are you getting understeer?
I'd love to see video. Car setup is very driver-specific, there's no such thing as one perfect car setup, as different people have very different driving styles.
Personally I don't mess with car setup much, I rarely have my car on the alignment rack during a weekend unless something has been tweaked. As long as I have good grip both front and rear and predictable behavior, I'd much rather concentrate on my driving, I ALWAYS know there's room for improvement there!
P.S. What tires and pressures are you running, don't forget that the tire is a spring, the tire manufacturers will give spring rates per psi for various tires, you can easily adjust overall spring rates with tire pressures.
What are the two ends of the car doing laterally? You're running your bars fairly soft.
I was never allowed to touch springs (spec series), so had to do all adjustments with shocks (stock Sachs two-ways) and bars, and was able to be competitive on a very wide range of tracks.
You say it's very stiff, but does that mean that you're breaking loose in the back when trying to get power down? Ie. what's the car's behavior (esp. at front and rear) going into, mid, and exiting the various corners? I don't know who your competitors were, but you've got a pretty stiffly sprung car. That's not necessarily a bad thing. Other than being hard on your kidneys (perhaps some extra seat padding?), how is it adversely affecting the car?
You say you're being outcornered because it won't set, I'm not sure I understand what that means exactly. You're not getting grip on the front end on corner entry and it's understeering on turnin and from turnin to apex? That could be your rear bar, and/or driving (the 996 Cup likes to be trail braked pretty aggressively to help rotate it).
See in a later post (this page) you mention understeer. Where exactly in the corner are you getting understeer?
I'd love to see video. Car setup is very driver-specific, there's no such thing as one perfect car setup, as different people have very different driving styles.
Personally I don't mess with car setup much, I rarely have my car on the alignment rack during a weekend unless something has been tweaked. As long as I have good grip both front and rear and predictable behavior, I'd much rather concentrate on my driving, I ALWAYS know there's room for improvement there!
P.S. What tires and pressures are you running, don't forget that the tire is a spring, the tire manufacturers will give spring rates per psi for various tires, you can easily adjust overall spring rates with tire pressures.
05-07-2012, 09:57 AM
#28
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05-07-2012, 12:53 PM
#29
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Chris,
Having no idea whether or not your LSD has been rebuilt and to what spec, anything we can say about it is really just a WAG other than to say that your breakaway torque on your test puts it in an acceptable range for it to be working. It may not be optimized, but it's not acting like an open LSD. I think you're going the right direction looking at the spring rate...
05-07-2012, 06:46 PM
#30
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