Nucci, I think you misunderstood. Although, show me a FWD BMW and I guess you have a point?

I was saying for the FRONT diff, I can't imagine too many situations where a clutch pack would be a good thing in an EVO. The rear is a clutch pack, and is desirable, basically what this whole thread is about.

As for the torsion diffs, I could be off, but I beleive the majority of the "limited slip" comes from the circumference of the gear, not the ends? The gears get pushed out radially, as well as axially, due to the helical cut, but the majority of the contact area is the circumference. I have seen some modifications on this idea like what you are talking about, but I have never looked into it. To me, you really don't want "lock up" in the wheels that steer. They need to be able to rotate at different speeds while cornering and if you want to minimize slip, that speed differential HAS to happen. A torsion diff does just that, splits up the torque and speed to where ever can use it best.

 

is torsion the same thing as torsen?

 

Thank you sir. Awesome information. I have been on these forums since 2004 and that is the best single post I have read regarding diffs. Kudos. . .

 

Yes, I believe "Torsen" is the correct terminology though. Someone let me know if I am wrong. Thanks.

 

Torsen is correct, spell check owns...

Who makes a Torsen style diff for the EVO that is tuned in the way nucci is suggesting?

 

probably no one? i was under the impression the helical was good enough for the front. i would assume going from the helical to aftermarket the improvements would be marginal at best? in any case if anything should go first its the rear

 

I don't think anybody does. I found the info regarding increasing/reducing friction at the gear end surfaces a few years back when Torsen was still supplying FSAE teams with differential gearsets and they had a technical document available. The details of adding torrington needle bearings behind the end gear faces were in there.

The more and more I see people making Evos into fast autocross cars, I'm convinced that the end goal is to make it throttle steer like an American RWD car. (I don't necessarily think this idea transfers to road racing or the streets though, due to differences in corner radius) Since the loaded front tire is so super-saturated by cornering force in comparison to the other tires, we need to get drive torque off the loaded front tire and onto the unloaded front tire and the loaded rear tire (this thread covers the rear diff in depth already). Whoever figures out how to do that first, or better than everybody else, will have an advantage.

The only reason I brought tech regarding clutch pack/ZF diffs is because as of now, nobody has (publicly anyways) shown how to make modifications to the front half (diff + ACD) of an Evo driveline in order to move drive torque from the loaded tire to the unloaded tire. Since nobody yet has the answer, they might as well have good information regarding the operation of all the available mechanical limited-slip diff styles, in order to be able to think up new crazy ideas to test - until there is a solution.

 

nucci,
GSC offers a 60/40 center diff. I didn't mention it because its simply...out of my budget.

 

i was debating between the gsc and just keeping the acd and getting it reflashed.. im not sure which performs better, it would make for an interesting comparison though

 

Depends upon what you do... My concern is making to the car too much RWD biased for a course with short radius corners...and then messing it up for when I run (someday) run on the big track.

 

A Torsen diff can also be tuned simply by changing the helical angle.

As this thread is lengthy and supposed to be about the rear diff, maybe we should continue front and center diff talk elsewhere?

 

Its about power oversteer... I'd say that you're more than on-topic.

 

Got to run an Evo today that had the Rear Diff upgrade. WOW does it make a ton of difference. Hope to do that early next year before the season starts.

 

i'm a little confused, could you clarify this? we want torque off the loaded tire and onto the unloaded tire? i'm confused how that would make a car corner faster - theoretically if a car is in an extreme turning situation wouldn't that just cause the unloaded tire to spin? doesn't it not have enough downforce to put down that power? esp if you think about a turn so extreme where the unloaded tire is nearly off the ground, and then you put the power down and there's almost zero downforce on that part of the car?

i thought the point was to make the loaded tire get as much of the torque as possible or something like that, but im no expert

 

if rwd cars are ok for track wouldn't a rear biased evo be fine as well? obviously with some set up changes to suit a track as opposed to something like an autocross. don't lambos and etc run like 10/90 at their most extreme?

im just not sure if the 60/40 is necessarily faster than an acd, or at least one with the acd tuned - otherwise wouldn't all the overseas competition evos switch to a rear biased center diff as opposed to tuning the acd? the 60/40 may very well be faster, i'd just like to see it in direct comparison to the acd system