Cusco Tarmac 35/65 Centre Diff
Jul 5, 2007, 06:32 AM
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Cusco Tarmac 35/65 Centre Diff
Howdy All,
I've searched for what I'm after but I just cant find it.
I want to run one of the 35/65 Cusco Tarmac Centre Diffs - But I cant find a definitive answer - are they available for the USDM Evolution? And if so, what style of centre diff do they fit in?
Many Thanks In Advance,
Jash
I've searched for what I'm after but I just cant find it.
I want to run one of the 35/65 Cusco Tarmac Centre Diffs - But I cant find a definitive answer - are they available for the USDM Evolution? And if so, what style of centre diff do they fit in?
Many Thanks In Advance,
Jash
Jul 6, 2007, 02:57 AM
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Jash,
From all the info I can find, which is next to nie, The Cusco 35/65 diff replaces the open centre diff in the gearbox with a planetry gear arrangement.
Due to the fact that standard evos torque is controlled either via the viscous coupling or the ACD (this is the limited slip part of the centre diff), torque split cannot be controlled front to rear as standard, as we all know. (much like a standard front or rear lsd, the LSD cannot set one wheel to have a 75/25 torque split at all times, it just controls the amount of slip, the more one wheel slips, the more the diff becomes closer to locked) Which is exactly what the ACD does, control slip, it can be locked, or pretty much open (if ACD) it can't choose to make more torque to the front or rear, its simply not in its design, and I can show you.
For the Cusco tarmac diff to work, a special planetry diff replaces the open centre diff, and as this diff now controls the torque split, the ACD/VCU needs to be removed (replaced), otherwise, they are simply going to try and override the 35/65 torque split.
I have heard that the Cusco diff is effectively an open diff, as it does not use clutch packs etc to control torque split, as this would make it a 50/50 "limited slip diff" much like any other LSD, which makes sense, but it does control the ratio of torque - torque split. (Any normal 50/50 centre LSD will have clutch packs, much like a normal LSD, its the gear design that alows for a 65/35 torque split)
As for the GSC 60/40 diff, I believe they use a spool to replace the VCU, but not a locked spool, an open spool. The VCU/ACD is the carrier for the center diff, without it the diff has only one bearing supporting it, and would flop around like an old mans weenie. But again, this seems to be a planetary diff, driving internal parts at differend speeds to induce a torque split (not geared output ratios)
Its a bit confusing, but with a decent driveline diagram, and some explanation I could probably help.
The Cusco Diffs are only stated for evos up to evo 6, as this was the last of the VCU'd cars - apart from some of the USDM evo's, therefor it the 6/7 centre diff is the same, you can use it in your 7, but removing some of the clutch plates from the ACD, or disengaging the pump to render the ACD inoperative.
PM me on the Evo Oz site (lostinthewoods) and I'll send you my number, give me a call, and hopefully I can clear some things up. (I am in Perth too).
Cheers,
Ruari
From all the info I can find, which is next to nie, The Cusco 35/65 diff replaces the open centre diff in the gearbox with a planetry gear arrangement.
Due to the fact that standard evos torque is controlled either via the viscous coupling or the ACD (this is the limited slip part of the centre diff), torque split cannot be controlled front to rear as standard, as we all know. (much like a standard front or rear lsd, the LSD cannot set one wheel to have a 75/25 torque split at all times, it just controls the amount of slip, the more one wheel slips, the more the diff becomes closer to locked) Which is exactly what the ACD does, control slip, it can be locked, or pretty much open (if ACD) it can't choose to make more torque to the front or rear, its simply not in its design, and I can show you.
For the Cusco tarmac diff to work, a special planetry diff replaces the open centre diff, and as this diff now controls the torque split, the ACD/VCU needs to be removed (replaced), otherwise, they are simply going to try and override the 35/65 torque split.
I have heard that the Cusco diff is effectively an open diff, as it does not use clutch packs etc to control torque split, as this would make it a 50/50 "limited slip diff" much like any other LSD, which makes sense, but it does control the ratio of torque - torque split. (Any normal 50/50 centre LSD will have clutch packs, much like a normal LSD, its the gear design that alows for a 65/35 torque split)
As for the GSC 60/40 diff, I believe they use a spool to replace the VCU, but not a locked spool, an open spool. The VCU/ACD is the carrier for the center diff, without it the diff has only one bearing supporting it, and would flop around like an old mans weenie. But again, this seems to be a planetary diff, driving internal parts at differend speeds to induce a torque split (not geared output ratios)
Its a bit confusing, but with a decent driveline diagram, and some explanation I could probably help.
The Cusco Diffs are only stated for evos up to evo 6, as this was the last of the VCU'd cars - apart from some of the USDM evo's, therefor it the 6/7 centre diff is the same, you can use it in your 7, but removing some of the clutch plates from the ACD, or disengaging the pump to render the ACD inoperative.
PM me on the Evo Oz site (lostinthewoods) and I'll send you my number, give me a call, and hopefully I can clear some things up. (I am in Perth too).
Cheers,
Ruari
Jul 6, 2007, 03:47 AM
#3
Why would you suggest that the ACD or VCU has to be removed when running the 35/65? They are both simply locking units, controlling when the rear wheels are coupled with the front wheels. The 35/65 torque split remains constant. Please explain.
Jul 6, 2007, 07:00 AM
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Exactly, if you have ACD/VCU in place they will essential try and lock the front and rear wheels.
The ACD/VCU will make the split 50/50 again. If you have a 35/65 split, this will allow the rear wheels to slip, as they have more torque, hence the reason why it is desired. If you have the ACD/VCU in place, it will try and control the slip.
Lets say you are coming out of a turn, the rear wheels are spinning slightly faster than the fronts due to the 35/65 diff, the ACD will detect this slip, and pressure will feed to the ACD to lock the ACD clutches. This will effectively lock the front/rear wheels = 50% torque split, counteracting the tarmac spec diff.
Don't forget that the actual centre diff in the gearbox i an open diff, and the ACD/VCU is the locking component from front to rear (the LSD part of the the centre diff). If you make the centre diff LSD with a cusco or GCS centre diff, you don't need two limiting slip components.
Or at least this is as I understand it. Please let me know if I am way off the mark.
The ACD/VCU will make the split 50/50 again. If you have a 35/65 split, this will allow the rear wheels to slip, as they have more torque, hence the reason why it is desired. If you have the ACD/VCU in place, it will try and control the slip.
Lets say you are coming out of a turn, the rear wheels are spinning slightly faster than the fronts due to the 35/65 diff, the ACD will detect this slip, and pressure will feed to the ACD to lock the ACD clutches. This will effectively lock the front/rear wheels = 50% torque split, counteracting the tarmac spec diff.
Don't forget that the actual centre diff in the gearbox i an open diff, and the ACD/VCU is the locking component from front to rear (the LSD part of the the centre diff). If you make the centre diff LSD with a cusco or GCS centre diff, you don't need two limiting slip components.
Or at least this is as I understand it. Please let me know if I am way off the mark.
Dec 20, 2009, 05:00 PM
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Exactly, if you have ACD/VCU in place they will essential try and lock the front and rear wheels.
The ACD/VCU will make the split 50/50 again. If you have a 35/65 split, this will allow the rear wheels to slip, as they have more torque, hence the reason why it is desired. If you have the ACD/VCU in place, it will try and control the slip.
Lets say you are coming out of a turn, the rear wheels are spinning slightly faster than the fronts due to the 35/65 diff, the ACD will detect this slip, and pressure will feed to the ACD to lock the ACD clutches. This will effectively lock the front/rear wheels = 50% torque split, counteracting the tarmac spec diff.
Don't forget that the actual centre diff in the gearbox i an open diff, and the ACD/VCU is the locking component from front to rear (the LSD part of the the centre diff). If you make the centre diff LSD with a cusco or GCS centre diff, you don't need two limiting slip components.
Or at least this is as I understand it. Please let me know if I am way off the mark.
The ACD/VCU will make the split 50/50 again. If you have a 35/65 split, this will allow the rear wheels to slip, as they have more torque, hence the reason why it is desired. If you have the ACD/VCU in place, it will try and control the slip.
Lets say you are coming out of a turn, the rear wheels are spinning slightly faster than the fronts due to the 35/65 diff, the ACD will detect this slip, and pressure will feed to the ACD to lock the ACD clutches. This will effectively lock the front/rear wheels = 50% torque split, counteracting the tarmac spec diff.
Don't forget that the actual centre diff in the gearbox i an open diff, and the ACD/VCU is the locking component from front to rear (the LSD part of the the centre diff). If you make the centre diff LSD with a cusco or GCS centre diff, you don't need two limiting slip components.
Or at least this is as I understand it. Please let me know if I am way off the mark.
On the CD9A/CE9A's W5m33 transmission, the VCU has never been co-located with the differential, so you can change the center differential and retain the VCU. This is the reason why the Cusco tarmac gear for the CD/CE9A just an open differential with a torque bias determined by the planetary gearing. Just like this:
Now, what you're suggesting is to leave the VCU out, but just as has been mentioned, that would make for just an open centre differential. I don't think that's a good thing.
The one person I have talked to who has a Tarmac gear left the VCU on and says that since the VCU takes a finite amount of time to lock up, the Tarmac gear has plenty of time to exercise its rear biased characteristics. Perhaps more importantly, the VCU does not redistribute torque per-se. All it does is link the two output shafts together so that in the event one end slips, the other is dragged along with it. Actually, I should mention that the w5m33's VCU resides in the rear output shaft and the differential body, but it does the same thing in that the short of it is that its action is slip dependent. It is worth remembering too that the Viscous Coupling doesn't really solidly lock up until a remarkable amount speed differential is detected. In fact, it still only transfers a limited amount of torque. I've heard that the w5m33 stock center viscous is rated at 16kgf per 100rpm? Not sure, but it's something along those lines.
Last edited by randedge; Dec 20, 2009 at 05:03 PM.
Trending Topics
Nov 5, 2015, 06:19 PM
#8
There use to be a fella racing his Evo 8 in TA here in California, Nils Laufsen (approximately spelled), supported by Robi Fuller and Road Race Engineering.
He used the Cusco 35/65 and I asked Nils how did he like it: he strongly advised me against using it.
According to him it did nothing to improve track performance.
I have received same advice by CliveW, a well known Lancer Evo transmission/trasnfercase/diff builder in UK for the MLR (Langer Register) racing crowd and builder of one of the coolest CP9A Evo V cars featured even here on EvoM.
I own 2 Evos, a 6.5 and 8.5.
So 6.5 with VCU and AYC, and 8.5 with ACD and RS diff.
Having setup both, 6.5 for road work (call it Tarmac Rally setup) and 8.5 for TA in California, I cannot see reason to change the center diff to 35/65: It will be way oversteering and not help to be faster.
For Gymkhana/Autocross (US parking lot pylon racing) I can see potential benefit for low to moderate power car: but not for high power car.
I would like to hear from knowledgeable person familiar with this diff in Evo V/VI, how would it interact with VCU or Quaife?
I am curious..and without total direct experience always tempted.
But can say from direct experience that my two car do not need anything- they are totally awesome.
He used the Cusco 35/65 and I asked Nils how did he like it: he strongly advised me against using it.
According to him it did nothing to improve track performance.
I have received same advice by CliveW, a well known Lancer Evo transmission/trasnfercase/diff builder in UK for the MLR (Langer Register) racing crowd and builder of one of the coolest CP9A Evo V cars featured even here on EvoM.
I own 2 Evos, a 6.5 and 8.5.
So 6.5 with VCU and AYC, and 8.5 with ACD and RS diff.
Having setup both, 6.5 for road work (call it Tarmac Rally setup) and 8.5 for TA in California, I cannot see reason to change the center diff to 35/65: It will be way oversteering and not help to be faster.
For Gymkhana/Autocross (US parking lot pylon racing) I can see potential benefit for low to moderate power car: but not for high power car.
I would like to hear from knowledgeable person familiar with this diff in Evo V/VI, how would it interact with VCU or Quaife?
I am curious..and without total direct experience always tempted.
But can say from direct experience that my two car do not need anything- they are totally awesome.
Nov 5, 2015, 06:27 PM
#9
There use to be a fella racing his Evo 8 in TA here in California, Nils Laufsen (approximately spelled), supported by Robi Fuller and Road Race Engineering.
He used the Cusco 35/65 and I asked Nils how did he like it: he strongly advised me against using it.
According to him it did nothing to improve track performance.
I have received same advice by CliveW, a well known Lancer Evo transmission/trasnfercase/diff builder in UK for the MLR (Langer Register) racing crowd and builder of one of the coolest CP9A Evo V cars featured even here on EvoM.
I own 2 Evos, a 6.5 and 8.5.
So 6.5 with VCU and AYC, and 8.5 with ACD and RS diff.
Having setup both, 6.5 for road work (call it Tarmac Rally setup) and 8.5 for TA in California, I cannot see reason to change the center diff to 35/65: It will be way oversteering and not help to be faster.
For Gymkhana/Autocross (US parking lot pylon racing) I can see potential benefit for low to moderate power car: but not for high power car.
I would like to hear from knowledgeable person familiar with this diff in Evo V/VI, how would it interact with VCU or Quaife?
I am curious..and without total direct experience always tempted.
But can say from direct experience that my two car do not need anything- they are totally awesome.
He used the Cusco 35/65 and I asked Nils how did he like it: he strongly advised me against using it.
According to him it did nothing to improve track performance.
I have received same advice by CliveW, a well known Lancer Evo transmission/trasnfercase/diff builder in UK for the MLR (Langer Register) racing crowd and builder of one of the coolest CP9A Evo V cars featured even here on EvoM.
I own 2 Evos, a 6.5 and 8.5.
So 6.5 with VCU and AYC, and 8.5 with ACD and RS diff.
Having setup both, 6.5 for road work (call it Tarmac Rally setup) and 8.5 for TA in California, I cannot see reason to change the center diff to 35/65: It will be way oversteering and not help to be faster.
For Gymkhana/Autocross (US parking lot pylon racing) I can see potential benefit for low to moderate power car: but not for high power car.
I would like to hear from knowledgeable person familiar with this diff in Evo V/VI, how would it interact with VCU or Quaife?
I am curious..and without total direct experience always tempted.
But can say from direct experience that my two car do not need anything- they are totally awesome.
8.5 - stock ACD? no tune? and when you say the RS diff, are you talking about the stock diff or a JDM 1.5 way RS diff?
Nov 5, 2015, 09:20 PM
#10
(Commenting on Evo 123, not sure about 4-9) If run with a viscous, it would theoretically run open and allow spin until the viscous coupling heats up from enough slip to lock and go 50/50. It should be used with well-set up front and rear diffs. Most reviews I've read say that it can be run without a coupling on a low-power car, but higher powered cars are going to want some sort of locking action. The speed output front & rear are the same when there is no wheel slip, but the planetary setup would indeed put more torque to the rear wheels (assuming 100% traction). The Tarmac's Achilles heel is that it is an open diff, and the car will be slower if you overpower an axle through a corner. It's good for braking and corner entry in theory, allowing independence between the front and rear diffs. In autocross, it's very useful for rotation, it will make the car act like a RWD without a coupling on it. Ideally, you'd want it to allow some freedom to rotate the rear end, but lock when there is significant wheelspin. Unfortunately, there isn't much of a solution for this to happen effectively; the viscous will take a second or two to heat up and lock, and that's a long time to be spinning.
I have a DSM/Evo123 Tarmac sitting here in a box and I ponder the what-ifs every day. It's a very polarizing part; I say if it's autocross or you want to have irresponsible fun with your Evo, it's a neat part to have. Extremely hard to find, though.
I have a DSM/Evo123 Tarmac sitting here in a box and I ponder the what-ifs every day. It's a very polarizing part; I say if it's autocross or you want to have irresponsible fun with your Evo, it's a neat part to have. Extremely hard to find, though.
Last edited by RS200; Nov 5, 2015 at 09:26 PM.
Nov 5, 2015, 11:52 PM
#11
Kyoo
normal OEM RS rear LSD...nobody I know of runs 1.5way on track in USA...cannot see reason to have LSD action under braking, on an Evo. That, to my knowledge is gravel setup, never to be used for street/tarmac/track.
The rear diff..and this is totally irrelevant to Cusco center diff discussion...is plated per Ralliart recipe with Ralliart plates...again irrelevant..but in case anybody finds that somehow important.
Typical Weir 12 plate works the same..so its just different approach to same problem with similar outcome.
ACD is stock, no tune.
Given the amount of grip on 275/35, 285/30 and 295/30, this car has, I doubt that ACD tune will affect much the behaviour.
On gravel/slippery I can see ACD reflash having a strong input.
I'll try it however- but nobody should expect miracles.
normal OEM RS rear LSD...nobody I know of runs 1.5way on track in USA...cannot see reason to have LSD action under braking, on an Evo. That, to my knowledge is gravel setup, never to be used for street/tarmac/track.
The rear diff..and this is totally irrelevant to Cusco center diff discussion...is plated per Ralliart recipe with Ralliart plates...again irrelevant..but in case anybody finds that somehow important.
Typical Weir 12 plate works the same..so its just different approach to same problem with similar outcome.
ACD is stock, no tune.
Given the amount of grip on 275/35, 285/30 and 295/30, this car has, I doubt that ACD tune will affect much the behaviour.
On gravel/slippery I can see ACD reflash having a strong input.
I'll try it however- but nobody should expect miracles.
Nov 6, 2015, 11:17 AM
#14
EvoM Guru
iTrader: (1)
Quaife has torsen center diffs. I would call to verify fitment though. The website is a bit unclear.
https://shop.quaife.co.uk/differentials?manufacturer=34
https://shop.quaife.co.uk/differentials?manufacturer=34
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