+35' toe-in for GT2 alignment. Why? Discuss!
12-20-2009, 10:41 PM
#16
Rennlist Member
Just shooting for a little bit of Occam's razor here, but is it possible that the car simply has too much power, i.e. you're twisting stuff out of alignment regardless of the static toe setting?
On another note, has someone mapped your rear toe through a full range of motion? Is it possible something's slightly bent or asymmetrical? Would it be worth getting a tilt kit to see if that changes things?
On another note, has someone mapped your rear toe through a full range of motion? Is it possible something's slightly bent or asymmetrical? Would it be worth getting a tilt kit to see if that changes things?
12-20-2009, 10:51 PM
#17
Race Car
I have run as high as ~+35' and it was not a pleasant drive, back end moved around alot, and car was .75 of a second slower. Once I got it down to the current settings the car has lapped faster and much more consistantly.
I think you could be surprised how much the car is squatting.... The stock rubber is not going to control all of that torque you have. As I said before, the GT2 had a tilt kit which reduced the squat. Porsche would have seen the isses as soon as they added HP and torque to these cars and then made the change. All of the RSCS and RSR cars only used the solid side mounts not tilt kits.
The construction of the slicks that were listed are quite different to the tires you listed. And dont forget these settings were for a car using 10-12 year old technology in the tires, there has been massive change in tire construction and performance in the last 10 years.
I know when we talked about it a few weeks ago you were thinking the Quaiff, and I am feeling the same way, If possible I would try and run a standard type LSD in the car (GT or similar). I am thinking the quaiff is having trouble regulating the huge amount of torque being put through it and moving the torque side to side causing the yaw effect. At the end of the day it really is about the HP you are running.
I noticed that BiiigHP's car does not experience the same issue, he runs a GT LSD doesn't he? and I believe he has the tilt kit.
I think you could be surprised how much the car is squatting.... The stock rubber is not going to control all of that torque you have. As I said before, the GT2 had a tilt kit which reduced the squat. Porsche would have seen the isses as soon as they added HP and torque to these cars and then made the change. All of the RSCS and RSR cars only used the solid side mounts not tilt kits.
The construction of the slicks that were listed are quite different to the tires you listed. And dont forget these settings were for a car using 10-12 year old technology in the tires, there has been massive change in tire construction and performance in the last 10 years.
I know when we talked about it a few weeks ago you were thinking the Quaiff, and I am feeling the same way, If possible I would try and run a standard type LSD in the car (GT or similar). I am thinking the quaiff is having trouble regulating the huge amount of torque being put through it and moving the torque side to side causing the yaw effect. At the end of the day it really is about the HP you are running.
I noticed that BiiigHP's car does not experience the same issue, he runs a GT LSD doesn't he? and I believe he has the tilt kit.
12-20-2009, 10:53 PM
#18
Race Car
Just shooting for a little bit of Occam's razor here, but is it possible that the car simply has too much power, i.e. you're twisting stuff out of alignment regardless of the static toe setting?
On another note, has someone mapped your rear toe through a full range of motion? Is it possible something's slightly bent or asymmetrical? Would it be worth getting a tilt kit to see if that changes things?
On another note, has someone mapped your rear toe through a full range of motion? Is it possible something's slightly bent or asymmetrical? Would it be worth getting a tilt kit to see if that changes things?
I remember someone had the rear suspension modelled, but just cant seem to find the info..... Anyone remember who did that?
12-20-2009, 11:00 PM
#19
Rennlist Member
Thread Starter
I have run as high as ~+35' and it was not a pleasant drive, back end moved around alot, and car was .75 of a second slower. Once I got it down to the current settings the car has lapped faster and much more consistantly.
As I said before, the GT2 had a tilt kit which reduced the squat. Porsche would have seen the isses as soon as they added HP and torque to these cars and then made the change. All of the RSCS and RSR cars only used the solid side mounts not tilt kits.
I know when we talked about it a few weeks ago you were thinking the Quaiff, and I am feeling the same way, If possible I would try and run a standard type LSD in the car (GT or similar). I am thinking the quaiff is having trouble regulating the huge amount of torque being put through it and moving the torque side to side causing the yaw effect. At the end of the day it really is about the HP you are running.
I noticed that BiiigHP's car does not experience the same issue, he runs a GT LSD doesn't he? and I believe he has the tilt kit.
I noticed that BiiigHP's car does not experience the same issue, he runs a GT LSD doesn't he? and I believe he has the tilt kit.
12-21-2009, 04:28 AM
#21
RL Technical Advisor
JMHO,......
I think Torque Biasing Differentials (Guard or Quaife) are great for FWD cars, AutoX'ers and street drivers, but they are a poor choice for anything used at the track for DE or competition.
I've broken a few of these in high HP applications, however my main complaint is the inability to keep the rear wheels locked together under trailing throttle that REALLY stabilizes the car. TBD's behave just like open differentials once you release the gas pedal.
Clutch-type LSD's are really the only way to go here regardless of whether you use the PMS version, the excellent Guard one, or an OS Giken.
I think Torque Biasing Differentials (Guard or Quaife) are great for FWD cars, AutoX'ers and street drivers, but they are a poor choice for anything used at the track for DE or competition.
I've broken a few of these in high HP applications, however my main complaint is the inability to keep the rear wheels locked together under trailing throttle that REALLY stabilizes the car. TBD's behave just like open differentials once you release the gas pedal.
Clutch-type LSD's are really the only way to go here regardless of whether you use the PMS version, the excellent Guard one, or an OS Giken.
12-21-2009, 11:23 AM
#22
Rennlist Member
JMHO,......
I think Torque Biasing Differentials (Guard or Quaife) are great for FWD cars, AutoX'ers and street drivers, but they are a poor choice for anything used at the track for DE or competition.
I've broken a few of these in high HP applications, however my main complaint is the inability to keep the rear wheels locked together under trailing throttle that REALLY stabilizes the car. TBD's behave just like open differentials once you release the gas pedal.
Clutch-type LSD's are really the only way to go here regardless of whether you use the PMS version, the excellent Guard one, or an OS Giken.
I think Torque Biasing Differentials (Guard or Quaife) are great for FWD cars, AutoX'ers and street drivers, but they are a poor choice for anything used at the track for DE or competition.
I've broken a few of these in high HP applications, however my main complaint is the inability to keep the rear wheels locked together under trailing throttle that REALLY stabilizes the car. TBD's behave just like open differentials once you release the gas pedal.
Clutch-type LSD's are really the only way to go here regardless of whether you use the PMS version, the excellent Guard one, or an OS Giken.
12-21-2009, 11:33 AM
#23
Three Wheelin'
Yikes you run a quiafe in your 993 tuner? Get that thing out of there ASAP and pick up a guard lsd 50/80. Don't put anything motorsport back there and just go with the guard trust me. Without it my 2wd setup would be uncontrollable in both accel and braking. With our cars we truely do need a locking diff which is something a gear driven LSD cannot provide. Great diffs for certain applications but cars like ours are not a place for this type of lsd.
You also need to be running significant toe in for the rear
KT is also adjustable with ERP arms and if not set correctly your can get strange behavior on accel.
The tilt kit can offer a little help but you'll find that the factory spacer is too big and should be trimmed
You also need to be running significant toe in for the rear
KT is also adjustable with ERP arms and if not set correctly your can get strange behavior on accel.
The tilt kit can offer a little help but you'll find that the factory spacer is too big and should be trimmed
12-21-2009, 12:28 PM
#24
Addict
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It's the diff.
I run the GT2 stiff axle kit, 2 degree neg with 10' of toe each side and have no issues with rear stability whatsoever, even with well over 400hp on stock RS dampers. I run a 9m modified carbon diff which we have fine tuned to match the needs of the 993 & Gt3, but as others have said you should be fine running a proper motorsport quality plate diff, start with a 50/80 setting for track use.
I run the GT2 stiff axle kit, 2 degree neg with 10' of toe each side and have no issues with rear stability whatsoever, even with well over 400hp on stock RS dampers. I run a 9m modified carbon diff which we have fine tuned to match the needs of the 993 & Gt3, but as others have said you should be fine running a proper motorsport quality plate diff, start with a 50/80 setting for track use.
12-21-2009, 01:46 PM
#26
Rennlist Member
Thread Starter
Guys, it seems like we are narrowing it down to zee diff. There goes another $5k into the black hole 
I believe you. Oddly enough, my car seems well planted and stable under braking at the track...but there is always room for imporvement! I had the Guard 40/60 in my last two Porsches and they worked very well.
Hey Spartan, how much toe are you running in the rear?
I still have the stock camber and Kinematic links (arms). The only one I changed is the ERP toe link.
What do you mean about trimming the "factory spacer"?
Good to know 
Do you use the "tilt" kit of the standard dimension solid mounts?
I think Torque Biasing Differentials (Guard or Quaife) are great for FWD cars, AutoX'ers and street drivers, but they are a poor choice for anything used at the track for DE or competition.
I've broken a few of these in high HP applications, however my main complaint is the inability to keep the rear wheels locked together under trailing throttle that REALLY stabilizes the car. TBD's behave just like open differentials once you release the gas pedal.
Clutch-type LSD's are really the only way to go here regardless of whether you use the PMS version, the excellent Guard one, or an OS Giken.
I've broken a few of these in high HP applications, however my main complaint is the inability to keep the rear wheels locked together under trailing throttle that REALLY stabilizes the car. TBD's behave just like open differentials once you release the gas pedal.
Clutch-type LSD's are really the only way to go here regardless of whether you use the PMS version, the excellent Guard one, or an OS Giken.
You also need to be running significant toe in for the rear
KT is also adjustable with ERP arms and if not set correctly your can get strange behavior on accel.
The tilt kit can offer a little help but you'll find that the factory spacer is too big and should be trimmed
KT is also adjustable with ERP arms and if not set correctly your can get strange behavior on accel.
The tilt kit can offer a little help but you'll find that the factory spacer is too big and should be trimmed
I still have the stock camber and Kinematic links (arms). The only one I changed is the ERP toe link.
What do you mean about trimming the "factory spacer"?
I run the GT2 stiff axle kit, 2 degree neg with 10' of toe each side and have no issues with rear stability whatsoever, even with well over 400hp on stock RS dampers. I run a 9m modified carbon diff which we have fine tuned to match the needs of the 993 & Gt3, but as others have said you should be fine running a proper motorsport quality plate diff, start with a 50/80 setting for track use.
Do you use the "tilt" kit of the standard dimension solid mounts?
12-21-2009, 01:50 PM
#27
Rennlist Member
In conjunction with the toe links, I think replacing the Kinematics with ERP bits really helps to 'tie down' the rear end. This was Steve W's advice to me and having done this with 2 cars now, I'm a believer. See my PM.
Perhaps doing that + appropriate LSD will cure what ails ya.
Perhaps doing that + appropriate LSD will cure what ails ya
.
12-21-2009, 01:53 PM
#28
Three Wheelin'
I'll check my alignment sheet when I get home. Kelly Moss setup the car for Road America and I can tell you whats on my sheets. Its alot of toe, enough to where you can see it just by looking at the car
GT2 tilt kits are just spacers for the rear subframe. The factory kit or spacer is too big and should made smaller
GT2 tilt kits are just spacers for the rear subframe. The factory kit or spacer is too big and should made smaller
12-21-2009, 02:55 PM
#29
Rennlist Member
Thread Starter
Thanks
12-21-2009, 03:06 PM
#30
Race Car
Looks like you are getting some good information here all round.
With the alignment specs, what ever you choose will be some form of compromise, you will need to just pick something (either track oriented or Street) and deal with the compromise. And there may be the compromise to deal with regarding tires etc as each one will "want" different specs to get the max performance out of them.
Cant wait to see the results of your choices......
With the alignment specs, what ever you choose will be some form of compromise, you will need to just pick something (either track oriented or Street) and deal with the compromise. And there may be the compromise to deal with regarding tires etc as each one will "want" different specs to get the max performance out of them.
Cant wait to see the results of your choices......