996GT2 diff ramps? What are the Cup Ramps
Discussion
The 996 gt3 and cup diffs use the same ramps- 50 deg on accel, 37.5deg on decel from memory, giving a 40%/60% lockup.
The lower the angle is the quicker the diff locks up.
The cup just uses a larger number of better quality plates along with a thicker washer to make the diff more aggressive and give significantly greater preload.
997 GT3 diff is quite a bit less aggressive. This might be a simple option if you are looking for something with steeper angles (less bite).
The lower the angle is the quicker the diff locks up.
The cup just uses a larger number of better quality plates along with a thicker washer to make the diff more aggressive and give significantly greater preload.
997 GT3 diff is quite a bit less aggressive. This might be a simple option if you are looking for something with steeper angles (less bite).
Edited by fioran0 on Wednesday 12th September 12:32
jfp said:
Does anyone know where I can get steeper than standard diff ramps for my 996GT2? we have measured the power ramp at 30 degrees, gut feel is a 45 degree ramp would be better. Does anyone know what Cup cars use. Cheers, Jon.
Hi John sorry to spam your thread dude, Im looking to purchase a 996 GT2 and ive taken a fancy to a red one in the classifieds... I believe you had an inspection done on this can you share any details with me please? It could save me a long journey.You can email me on UGGS4U@YAHOO.COM
Cheers Uggs
jfp said:
The current ramps cause full lock up too early in the torque delivery, hence the car pushes on with very modest throttle inputs. Thanks, Jon
The Cup set is massively more aggressive than the street one. If you think you are pushing now!!!Are you 100% sure what Diff you have in there? Is it def a stock diff and def stock street internals.
You may need to just try to work with the diff more rather than against it. (trail brake harder)
Are you sure it's also not a setup based issue rather than diff based. It's perfectly possible to get at a balance where any throttle washes out the front and it's nothing to do with the diff.
Edited by fioran0 on Wednesday 12th September 12:35
fioran0 said:
The Cup set is massively more aggressive than the street one. If you think you are pushing now!!!
Are you 100% sure what Diff you have in there? Is it def a stock diff and def stock street internals.
You may need to just try to work with the diff more rather than against it. (trail brake harder)
Are you sure it's also not a setup based issue rather than diff based. It's perfectly possible to get at a balance where any throttle washes out the front and it's nothing to do with the diff.
Once you've driven through the initial locked diff/push/plough on understeer (and yes it is that bad/noticeable) and in the process stabilized/got the front end turned in, the car hooks up perfectly and drives as you'd expect it to Neil.Are you 100% sure what Diff you have in there? Is it def a stock diff and def stock street internals.
You may need to just try to work with the diff more rather than against it. (trail brake harder)
Are you sure it's also not a setup based issue rather than diff based. It's perfectly possible to get at a balance where any throttle washes out the front and it's nothing to do with the diff.
The understeer happens at very small and gentle throttle openings, it does so at 30,40,50mph. We're not talking about the car being driven hard or "aggressively" here. More driven in a very "normal" everyday fashion.
sportsandclassic said:
Was it you I spoke to a few weeks back ? Have had two people on about this on a GT2....
Hello Mike, yes it was indeed. Its a big problem on the GT2, on both power and overrun. The car should work very well, but the diff is a bigger problem than people realise, certainly even more so than Geo... Jon. Slippydiff said:
Once you've driven through the initial locked diff/push/plough on understeer (and yes it is that bad/noticeable) and in the process stabilized/got the front end turned in, the car hooks up perfectly and drives as you'd expect it to Neil.
The understeer happens at very small and gentle throttle openings, it does so at 30,40,50mph. We're not talking about the car being driven hard or "aggressively" here. More driven in a very "normal" everyday fashion.
Gotcha,The understeer happens at very small and gentle throttle openings, it does so at 30,40,50mph. We're not talking about the car being driven hard or "aggressively" here. More driven in a very "normal" everyday fashion.
If the OP was trying to describe what you did in your post then that's really just working diff behaviour sadly.
The lowish speed push that catches you when you are just trying to get round a motorway exit ramp or similar?
The cup set up is exactly the opposite of what he needs then. Discs that hold much harder and have 10 times more preload are even less fun in those situations.
Practically speaking, all you can really do is run a weaker diff to avoid it and accept the lower assistance when pushing hard or suck it up and learn to be patient with the throttle in some situations knowing you will gain from it in others.
Experimenting in other areas (pressures for one) can sometimes provide surprising workarounds. (exact same issue on CS)
Sometimes, and it pains me to say it given my binary mindset, there's only ever imperfect solutions. Even the mighty F1 needs to swallow that bitter pill.
Maybe that's what used to be called the character of a car. All the little nuances that amazed or infuriated you.
My inner teenager is dying to shout, you've got bags of power and only rwd. Every single corner you encounter should require opposite lock. What's this under steer jibber jabber
Edited by fioran0 on Thursday 13th September 00:39
fioran0 said:
Gotcha,
If the OP was trying to describe what you did in your post then that's really just working diff behaviour sadly.
The lowish speed push that catches you when you are just trying to get round a motorway exit ramp or similar?
That's the one.If the OP was trying to describe what you did in your post then that's really just working diff behaviour sadly.
The lowish speed push that catches you when you are just trying to get round a motorway exit ramp or similar?
fioran0 said:
The cup set up is exactly the opposite of what he needs then. Discs that hold much harder and have 10 times more preload are even less fun in those situations.
IMHO the GT3 exhibits that behaviour too though I wonder if the torque of the GT2 exacerbates things (since its load and not speed differentials that lock diffs
IMHO the GT3 exhibits that behaviour too though I wonder if the torque of the GT2 exacerbates things (since its load and not speed differentials that lock diffs
Precisely the conclusion that we've come to Neil. Not such an issue with the N/A car as it doesn't have the low down AND near instant torque build up that a re-mapped GT2 has.
fioran0 said:
The only thing you can really do is run a weaker diff to avoid it and accept the lower assistance when pushing hard or suck it up and learn to be patient with the throttle in some situations knowing you will gain from it in others.
Experimenting in other areas (pressures for one) can provide surprising workarounds.
Sometimes, and it pains me to say it given my binary mindset, there's only ever imperfect solutions. Even the mighty F1 needs to swallow that bitter pill.
Maybe that's what used to be called the character of a car. All the little nuances that amazed or infuriated you.
I've taken a look at the OS Giken diff, it looks nicely (and cleverly) engineered. I know the Jap guys use them in their big horsepower drift cars and suchlike. I wondered if they'd be any good in a 911.Experimenting in other areas (pressures for one) can provide surprising workarounds.
Sometimes, and it pains me to say it given my binary mindset, there's only ever imperfect solutions. Even the mighty F1 needs to swallow that bitter pill.
Maybe that's what used to be called the character of a car. All the little nuances that amazed or infuriated you.
Having seen what JFP has been through with his car over the past few months, I suspect a large majority of the issues my first 996 GT2 suffered with, lay with the diff . . . .
Slippydiff said:
I've taken a look at the OS Giken diff, it looks nicely (and cleverly) engineered. I know the Jap guys use them in their big horsepower drift cars and suchlike. I wondered if they'd be any good in a 911.
Having seen what JFP has been through with his car over the past few months, I suspect a large majority of the issues my first 996 GT2 suffered with, lay with the diff . . . .
we used an OS Giken diff in our yellow 965T race car, superb kit!.. I have a source for them also.Having seen what JFP has been through with his car over the past few months, I suspect a large majority of the issues my first 996 GT2 suffered with, lay with the diff . . . .
All good comments here... Off power the diff with cup plates and 80 lb pre- load is fine. On hard power cornering load its fine. Don't forget even with that pre-load and no throttle the diff is open, will slip, until the ramps are working. I'm convinced a steeper power ramp that resists working I.e locking the diff, set up for the GT2 will work well. I may swap the power and over run ramps and try it over the weekend to prove out...
I bow to you superior knowledge on ramp angles. The one area of the car I can never fathom out is the gearbox or diff! I understand the principles, I've seen the parts, but I still couldnt re-assemble the jigsaw like i could an engine. Thankfully I know a man who can 
I'm reading all this and if I understand your problem correctly you are suffering low speed power on understeer.
The first thing I thought was tyres. Buy new and buy sticky, a sticky trackday tyre. I find these allow the car to balance out, particularly with regards turn in. The front is light and the balance between grip and slip is extremely delicate. Far more so than the rear where all that weight is forcing the tyres into the Tarmac.
The next thing I thought was tyre pressures, my gut feel is too high on the front but you would need to work that out for yourself.
The final thing was suspension. Either the dampers themselves or the roll bars. Softer front bars / stiffer rears. I am assuming you have fixed dampers and so can't adjust bump or rebound.
I'm ruling out any driver error of course
I wouldn't be coming back into the pits asking for a diff swap at this stage.
A road car is designed to understeer first because it's easier to deal with than oversteer. In truth although everyone talks about taming the back end of a 911 I think it's all about keeping that front end in contact with the road. On a normally aspirated car it's much easier because you have a very progressive throttle. Turbo charged cars don't have this, the power comes in with a bang some time after you asked for it.
Good luck
I'm reading all this and if I understand your problem correctly you are suffering low speed power on understeer.
The first thing I thought was tyres. Buy new and buy sticky, a sticky trackday tyre. I find these allow the car to balance out, particularly with regards turn in. The front is light and the balance between grip and slip is extremely delicate. Far more so than the rear where all that weight is forcing the tyres into the Tarmac.
The next thing I thought was tyre pressures, my gut feel is too high on the front but you would need to work that out for yourself.
The final thing was suspension. Either the dampers themselves or the roll bars. Softer front bars / stiffer rears. I am assuming you have fixed dampers and so can't adjust bump or rebound.
I'm ruling out any driver error of course
I wouldn't be coming back into the pits asking for a diff swap at this stage.
A road car is designed to understeer first because it's easier to deal with than oversteer. In truth although everyone talks about taming the back end of a 911 I think it's all about keeping that front end in contact with the road. On a normally aspirated car it's much easier because you have a very progressive throttle. Turbo charged cars don't have this, the power comes in with a bang some time after you asked for it.
Good luck
Edited by Henry-F on Thursday 13th September 08:59
jfp said:
All good comments here... Off power the diff with cup plates and 80 lb pre- load is fine. On hard power cornering load its fine. Don't forget even with that pre-load and no throttle the diff is open, will slip, until the ramps are working.
Your preload if its at 80lbs is your problem. Tracked GT3s running higher preload have been trying to work around exactly your problem when driven on the street for many years. 80Nm is the unofficial limit if you are happy to still accept a bit of push on the street but don't want real headaches in the wet or tight corners (ie out of a junction). That's 60 ft lbs. The more preload, the quicker and snappier the diff reacts when asked to. It becomes more on/off as preload increases.
If you were running street spec pre load (5-15nm) then you would need more throttle and for longer for it to get up to full lock on accel and the transition from off to on would be much more progressive.
Total lock remains the same, you just get a smooth curve up to lock rather than a binary function.
Edited by fioran0 on Thursday 13th September 11:17
jfp said:
I'm convinced a steeper power ramp that resists working I.e locking the diff
Can you clarify what you are meaning here?The steeper the ramp angle, the less lock up you get. so 20% lock is something like 75 deg ramp angle.
The greater the preload, the less it takes for the diff to lock up.
It reads as though you are misunderstanding how the clutch plate type works. It doesn't work by resisting the urge to lock. You weaken preload to make it more gradual to full lock and increase ramp angle to make the amount of total lock lower.
Edited by fioran0 on Thursday 13th September 11:28
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