cusco tarmac spec center diff
CUSCO Tarmac Gear Mitsubishi Lancer Evolution I~III CD9A CE9A

Sirnixalot said:

cusco tarmac spec center diff
CUSCO Tarmac Gear Mitsubishi Lancer Evolution I~III CD9A CE9A

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I know where to get it, and I can get it cheaper.
I wanna hear what it's like.

Here's some pics of my Cusco Tarmac Gear in various stages of disassembly:



And here's the sleeve that comes with it, that can be used to replace the stock VC:

I know Charles likes his(tarmac) from everything I've read that he as posted. Scott are you 100% happy with yours? Was it worth the cash ECT. Thanks for the pics. They can be very hard to come by!


Kevin

So what would a Quaife front diff, 4 spider center diff and the TRE MaxLock rear diff be like in a road racer?
Is that a true 50/50 split F/R?
I do not auto-x at all, never tried it, and have no desire to.

I do not like drifting, in fact I down right loathe it.

I just don't want to spend $2k+ on something that I may/may not like.
Plus it take over 28 days to get one in from Japan.

For now, I'm going to get a Quaife installed up front when my transmission gets rebuilt...

How hard would it be to install the Tarmac Gear at a later date?
Does it require a full tear down, or is it simply splitting the cases, removing the 4 spider center diff and dropping in the new Tarmac Gear?

Strm Trpr said:

So what would a Quaife front diff, 4 spider center diff and the TRE MaxLock rear diff be like in a road racer?
Is that a true 50/50 split F/R?

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Yes, that setup would be a 50/50 split. The only compromise would be the slow reacting (~2 seconds) center VC. So for example, if one end of the car started spinning up the tires, it could take a couple seconds for the center to transfer power to the opposite end. However, with the Quaife LSD up front and the MaxLock LSD out back, you'll be less likely to experience massive wheel spin at only one end of the car.

Strm Trpr said:

How hard would it be to install the Tarmac Gear at a later date? Does it require a full tear down, or is it simply splitting the cases, removing the 4 spider center diff and dropping in the new Tarmac Gear?

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You could do it with the trans still installed. Just pop off the fist two sections of the case, swap in the Cusco, check/adjust the preload, and seal it back up. It'd be kinda awkward working with the trans on its side like that, but it certainly could be done.

greengoblin said:

Scott are you 100% happy with yours? Was it worth the cash ECT.

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When my car had all stock front, 2-spider center, and rear LSD differentials, it was an understeering pig when accelerating out of a corner. Then my 2-spider center ate itself. So I replaced it with the Cusco Tarmac Gear 35/65, still using the center VC.

With the Cusco, the car suddenly drove like a RWD. The corner exit understeer was replaced with oversteer when hard on the throttle. It was awesome!!! But unlike a RWD, if I kept my foot planted long enough, the VC would eventually lock up and the front would pull the car straight again. Best of both worlds!

However, there was one drawback... With most of the power being sent to the rear, it quickly highlighted the limitations of the stock rear VC. I was getting massive inside-rear wheelspin on corner exit for a good 2 seconds before the rear VC heated up enough to lock. We're talking smoke show wheel spin if I didn't back off the throttle. I needed a faster locking clutch-type EVO rear LSD.

Then I stripped 3rd gear and grenaded my transmission before I could install an EVO rear diff. I swapped in another tranny with a 4-spider center diff, TRE's front RipGrip diff, and installed the EVO rear diff at the same time. So I was back to 50/50, but with a fast locking rear.

The end result was surprising... with the rear EVO diff I was able to initiate oversteer, and the front RipGrip greatly diminished understeer. No massive wheel spin at either end. It's actually a pretty good setup!

Over winter I plan to finally swap the Cusco in the new transmission. Then I'll have the front RipGrip, center 35/65, and rear EVO diffs. It should be quite interesting!

So to answer your question; is the Cusco worth the $2K price tag...? It's hard to say. It's twice the price of a 4-spider. And with proper front & rear LSD's you can achieve a pretty good setup. But I suspect that come Spring when I try my car with its latest driveline configuration, I'll be happy I made the investment.

Thanks so much for the taking the time to give us such great feedback. PLEASE check back in once you bang on the new setup!

Kevin

In this thread there was some talk about using a worn out VC wit the tarmac. I've read about this other places too. Has anyone used or seen the Ralli Art VCU replacement or the clutch style replacement found here.

Ralliart viscous coupling revealed.. | Galant VR-4 > Technical Discussions | GalantVR-4.org Mitsubishi Galant VR4 Forum

Seem like some really neat stuff though very hard to find.

OK so I just want to be perfectly clear before I do this. Regardless if I put an EVO 3 or EVO 8 (I read they were the same) in the rear slot on my 1G, I will need axle cups from an EVO 8 OR a 3 bolt 1G NON LSD. Is that correct?

greengoblin said:

In this thread there was some talk about using a worn out VC wit the tarmac. I've read about this other places too. Has anyone used or seen the Ralli Art VCU replacement or the clutch style replacement found here.

Ralliart viscous coupling revealed.. | Galant VR-4 > Technical Discussions | GalantVR-4.org Mitsubishi Galant VR4 Forum

Seem like some really neat stuff though very hard to find.

Click to expand...

Found more info on this and thought I should post it up so people could read through it if they want.


Ralliart viscous coupling RA737828A1 - 4GTuner

SLO MO VIDs: Welded vs Stock at LAUNCH! - 4GTuner

Ralliart viscous coupling RA737828A1 - 4GTuner


You may be able to find one here:

Cheap car parts, Engines & Textspares Parts. Find used car parts & car spares from online car breakers

With the Cusco, do you still have to run a VC in the center? Or can that be removed?

97gst_spyder said:

With the Cusco, do you still have to run a VC in the center? Or can that be removed?

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With a small search you could have found that out you can run with or w/o it.

97gst_spyder said:

With the Cusco, do you still have to run a VC in the center? Or can that be removed?

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More info here: http://www.dsmtuners.com/forums/road-course-autocross/400884-lets-talk-difs.html

just reading up on cusco tarmac centerdiff. I would like to try one of these. I see that this was tried here with the factory VC in place. I build transmissions so I understand how the center diff operates. It seems to me running a factory VC would be a very bad idea with this tarmac diff. the VC operates when it sees anything other than a 50/50 split. when front spins 60/back 40 the VC fluid thickens and locks the clutch plates bringing back the 50/50 split. or attempt to anyway. it may only be able to prevent a 70/30 spin and keep it at 60/40. but rest assured the plates are working and churning away inside with anything other than 50/50 split.

to look at it another way the factory VC is not about distributing power 50/50. it about limiting wheel speeds front to back axle. when all tires are same size and car is driving forward the VC does nothing. the clutch plates are stationary inside. its only when wheel speeds of front or rear axle changes from 50/50 split does the VC do anything.

now with this 35/65 diff installed the VC would be working overtime ALL THE TIME. it does not have the abilty to allow 35/65 split and do nothing. its a mechanical coupling that does its job to limit spin front to rear when anything other than 55/50 is present. this tarmac diff with its 35/65 split is splitting wheel speeds. yes it takes more power to drive the rear than it does the front. but it is doing that through a planetary gear ratio change on one of the outputs.

so a few things will happen if you use the factory VC with this diff. A you wouldnt be getting the 35/65 split the diff is designed to give. the VC would be working to bring back to factory 50/50 split. B the VC would certainly over heat as its not designed to slip inside all the time. C it would be costing some WHP loss as a lot of energy would be lost inside the VC. add all that up and its seems a very bad idea to me.

Jerry,

I'm not sure you understand how our center differential works. During normal driving there is no speed difference between the front and the rear, even with the cuzco. The VCU is irrelevant.

I think the VCU is needed with the cuzco, is does not look like it has an internal clutch pack. When it encounters wheel spin it will goto the 35/65 split, but it can only transmit as much as the fronts have traction. So whatever torque the front has, you'll have 65/35 of that. If you add in a clutch, that will allow you to approach a 0/100 split. depending on how little traction the front has, and how much torque the clutch can transmit.

http://www.stealth316.com/2-awd3.htm#cdvcu according to that it should only be 50/50 when there is no wheel spin, and 35/65 when there is.

such a thorough article but the author is incorrect in his conclusions of how this TQ split occurs. he disagrees with mitsubishi explanation. I agree with mitsubishi.

the 35/65 TQ occurs when driving straight. the VC does nothing driving straight. the VC used with cusco tarmac works when there is anything other than a 35/65 split.. the authur is getting confused by his understanding of how a planetary gear set works in an a/t transmission. in the case of a/t planetary gearset can have different gear ratios depending on which gears in the planetary are locked. in the case of AWD car the planetary is attached to output of one axle. and it is never locked. it is always driven by the same one gear. wheel speeds front to rear will always be different. the planetary gearset essentially acts like an open diff to allow these different wheel speeds.

in the case of normal 4g63 AWD car if you weld VC coupler you will have 50/50 split all the time. if you weld VC with a tarmac center diff you will have a 35/65 split all the time.

my mistake was mechanically putting the 35/65 split before the VC in the driveline. the 35/65 split is applied after the VC.

No, if you lock a tarmac you get 50/50. The 35/65 is only developed through a speed difference in the ouputs.

bastarddsm said:

No, if you lock a tarmac you get 50/50. The 35/65 is only developed through a speed difference in the ouputs.

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I disagree. the planetary applies a 35/65 split whether the VC is locked or not. it is independently applied to one axle

the 4g63 has a 50/50 split whether or not the VC is locked or not. same final drive is applied to both axles.

with the tarmac. the same final drive is not applied to both axles.. one axle has a planetary gear set multiplier.

Yeah, and if the outputs of the planetary are locked together the "planetary gear set multiplier" is taken out of the equation.

The 35/65 is because it it would spin the fronts 2.85 times faster than normal if the rears were stopped, and then the rears would turn 1.53 times faster if the fronts were stopped.

A 50/50 would be 2 times faster.

If it worked like you said 3000GT's would burn up VCU all the time as they have a simlilar VCU to a dsm and the CD is just like a tarmac.

i give up. you dont understand how a VC works or a planetary drive. neither is ever locked in and AWD car during any kind of driving.

No I understand it perfectly. Explain to me how the VCU in a 3/s survives when it has a planetary CD with a 45/55 power split?

Jerry, the stock center VC doesn't come into play until there is a wheel speed differential between the front & rear drive wheels.

I have a Cusco Tarmac Gear center diff. If I accelerate hard enough to break the tires loose, then the rear always breaks loose first. The center VC then begins to heat up and 2 seconds later it locks, changing the torque distribution from 35/65 to 50/50.

In many cases this is a good thing. You break the rear loose, the tails hangs out, and as the VC heats and locks it transfers 50% of the torque to the front and helps pull the car straight again.

I have used my Cusco Tarmac Gear both with and without the stock center VC. When I run the car without the VC, it behaves just like a RWD car. You can hang the ass out (assuming you can break traction) and drift. Quite fun, but not always the fastest way around the road course.

I will try to explain..some of the lingo may be off so dont beet me up on that.

to simplify this explanation lets look at a fwd drive train because it is much easier to understand.. there are two axles. left and right. and one center diff between them. driving straight these two axles turn at same speed when tires are same diameter. the diff is doing nothing. if there were clutch plates on this diff they would also be doing nothing.

now lets install a taller tire on right side of car. now driving in a straight line the right axle will be turning slower all the time. the diff will be turning all the time. if there are clutch plates attached to diff they will be churning and burning. they are not designed to slip and grab at all times.

now lets apply a fictional second differential in the middle of right axle. now the center diff no longer spins all the time. the clutch plates are again stationary. the second diff is spinning all the time. the tires are rotating at different speeds. you have a tq split proportional to these different wheel speeds.

now heres the cool part. the planetary is doing the job of both diffs in the above scenario. it does both jobs simultaneously. in an A/T a planetary diff has three potential different gear ratios depending on which gear is the drive gear . in the case of this AWD application the planetary is never locked. and it gets power input through two different places. each place gives a different gear ratio output. input one has the clutch plates attached to it and drives both front and rear axle sets.. input two drives one axle set and applies a secondary gear ratio to that one axle. power input one allows the clutch plates to be stationary. power input two allows a TQ split between front and rear axles that is applied at all times. if an awd vehicle has a planetary center diff with a tq split the front and rear axles will be turning at different speeds. all thats needed to prove this is a high speed camera and slow motion drive by of the vehicle.