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s15 helical vs. 2-way

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  • s15 helical vs. 2-way

    I know this has been discussed many times on other forums (and I've seen it a few times here)...

    I can basically trade straight up for an S15 Helical (entire pumpkin ready to bolt in) for my Tomei 2-way differential this winter.

    My application is mostly HPDE, some street (spirited driving/hwy), some drag on rare occassions, never drifting other than an occassional slide for kicks. I'm honestly sick of the noise of a 2-way, but moreso how the car feels. i'm not an experienced driver, but it definitely feels very "drifty" to me. i've had a few close calls with the back end stepping out, and i've READ that the helicals help with this. Also, hard braking with the 2-way is a bit scary. I've heard the Tomei can be made less aggressive, but I've also heard the adjustability margin is slim.

    Am I taking a step in the right direction? I've read the pros and cons of both but I'd like to hear from people who have experience performance driving both. most of the feedback on the other forums are from those heavily into drifting. of course the clutch is the way to go for that application.

  • #2
    My car is about 95% street driven, with a few track days here and there. I've also ridden in and driven cars with clutch-type diffs. They were all Kaaz as luck would have it, not Tomei.

    The clutch diff was noisy and even in an ordinary turn (pulling out of the parking lot) made the back end squirrely. Admittedly the car was set up for drift, so the owner probably wanted it that way. I know there is adjustability in these, depending how the clutch packs are set up, but that seems like a lot of work to do especially if you need to change it depending on the events your participating in.

    The helical diff is much more progressive - it goes from invisible to locked in a linear manner, unlike the clutch-type which was more of an on-off switch. I love it for on-ramps and country roads, even at relatively low speeds. For the driving I do I'd only pick a clutch-type diff if there was no helical option. The helical makes no noise and is basically seamless in its operation.

    I think if you're doing mostly track days and street driving, a helical might be the way to go. Just my opinion though.
    1990 S13, SR-swapped "Budget Baller" - gone down the road...


    • #3
      I've experienced both a clutch type (kaaz unit) and an s15 helical. I started off with a clutch type. I frequent auto-x and track days, and I also use my car for daily driving. I could not stand the clutch type after the few months. I had a bit of the problems yourself and Rittmeister mentioned. It did things I didn't want it to, and then some. Ever since I switched to the s15 I couldn't be happier. It's maintenance free, it's great on and off the track, and it puts the power down very smoothly. I think you'd be happy with the s15 unit.


      • #4
        thanks for the input guys. kaaz and tomei are pretty similar from what i've read and experienced. both aggressive 2-ways compared to say a gtr rear or the mild nismos. i am slowly leaning towards helical, and yes the on-off drifty feel of the 2-way isn't really the driving feel i am after for the time being. i might give the helical a go this winter


        • #5
          Why wouldn't you want a 1.5-way diff instead of a 2-way?


          • #6
            I had a 1.5 way clutch type. Under acceleration out of corners, with the both wheels locked, caused the car to bog around the corner. That drove me NUTS. Although my plates were set to 100%, then down to 80%, and after paying 200 dollars for a shop to do it I still had the same problem. You can fine tune the lock, and if you have a bit of cash/time then it might be worth it. But in my opinion, having a low maintenance unit means I have more time to drive my car than fix it. A clutch type that looks very promising is the OS Giken, but I'm always weary about trying clutch type diffs :X


            • #7
              The 1.5-way is supposed to help turn in, as it gives the wheels less lock during decel. It will behave the same as a 2-way diff when you accel out of a corner.

              Have you tried the uber clutch diff, known as the ATS/Carbonetic (ATS-Across's name here in the USA) Carbon Diff?

              Jason Rhoads used that diff, and loved it. Reason being is that, the carbon plates allow for a certain amount of slip before they lock up, and when they lock up, they lock up very well due to the nature of cabon plate on carbon plate + heat.

              They last a long time too, as carbon discs wear down less than metal discs do.

              That's all from what I've heard from people who have used it, and what the brochure says, but not from personal experience, so take what I said with a grain of salt, but do remember, some of these people who have made those claims have achieved some amazing feats (Jason Rhoads), so their opinions do matter.


              • #8
                the only thing i don't like about the helical is if you lift the wheel up or take the weight off the wheel it spins like a open diff. very annoying on the track. i'm thinking a 1.5 would allow power to be added sooner and not spin the outside tire.

                I would love to try both but only have experience with the helical.

                i may be able to cure the lifting with better suspension setup in the back.

                Most PM answers: F 17X9 +22, R 17X9 +35


                • #9
                  Originally posted by Your Mom
                  I would love to try both but only have experience with the helical.

                  i may be able to cure the lifting with better suspension setup in the back.
                  Before you go playing with the rear suspension we should swap cars on track to compare. The 86XX out back has alot less droop than the OTS koni's you have, but I'm not sure if that is an issue or not, as I never drove with the OTS yellows on track.


                  • #10
                    Originally posted by Your Mom
                    the only thing i don't like about the helical is if you lift the wheel up or take the weight off the wheel it spins like a open diff.
                    A clutch diff is going to do that too. At least, one you're going to want to use for autox/street/grip. The breakaway is only a few dozen ft-lbs. I've hung myself on my driveway with a KAAZ 1.5 way.

                    What I didn't like about the clutch diff is that when you go to apply the power at corner exit, you can feel the nose of the car lurch to the outside as the rear wheels lock together. Never had any issues with noise or clunk on the street with the addition of Ford friction modifier and turning it to 80%. This was on the 4 plate version, not the 12 plate one. I switched to an S15 diff and I'm never going back, just on how it feels in the car.

                    About the ATS diff... It's an expensive proposition to find out if you like it or not. They're the priciest clutch diff around!
                    She's built like a Steakhouse, but she handles like a Bistro.


                    • #11
                      I definitely prefer the Torsen diff in my S2000 to my Kaaz.
                      Cory B.

                      "Driving a race car as fast as possible is all about maintaining the highest possible acceleration level in the appropriate direction."


                      • #12
                        I had the Nissan R32 diff for a while and hated it both on the street and at the track. It chattered like crazy even with many kinds of additive and pushed out anytime I applied throttle. I think they are a 1.5 diff. I also had a 1.5 Kasz or whatever they are called. It acted the same. Helical is wonderful. Set up the car to not lift a rear tire and don't limit the travel too much and it works great. A stiff rear sway and you might as well forget it though. I run stock or none on the rear.


                        • #13
                          The TRE site has a good run down on the difference between differentials.

                          They prefer Quaife style torque biasing diffs over clutch diffs due to there variable smooth engagement, less negative handling effects, lower maintenance, and lower setup labor.

                          Adjusting the lockup torque on a clutch type eliminates a lot of the negative handling characteristics experienced with super aggressive lockup torques.

                          I have a US Nismo 2 way with 75 ft. lbs. breakaway torque and it does not suffer from the poor turn-in and push issues of high torque set diffs.

                          Bottom line is - if you want a clutch diff to handled well get a good quality one that can adjust breakaway, initial engagement feel, and ramp angle so you can tune it to work.

                          NISMO site on diff adjustment -

                          MotoIQ OS Giken LSD Tuning Article -

                          The Nerd shall inherit the podium for knowledge is power.


                          • #14
                            I believe only the highest end Nismo LSD allows you to actually change the initial torque settings by using a breaker bar and a socket to turn a nut or whatever it is.

                            I think it's the GT Pro LSD.

                            The older SSS LSD had the same feature, and the GT Pro replaced the SSS.


                            • #15
                              ive only ever ran the s15 diff and aside from lifting a tire or getting stuck in the snow/ice i havent had any problems w/ it. im running no rear sway for now.

                              heres a great article that was shown to me by an old roadracer, it explains how the torsen works.


                              "How It works:
                              In the Torsen, as in any other differential, the power of the engine is transferred to the differential housing via the ring gear. The Torsen then uses pairs of worm wheels (from two to three pairs, depending an the size of the differential) mounted on the differential housing to turn the worm gears splined to the axle shafts. The left worm wheel of each pair turns the left axle shaft, and the right worm wheel of each pair turns the right axle shaft, Because the worm wheel cannot turn the worm gear, it locks on the gear and turns the axle shaft, propelling the vehicle forward. The right and left axle shafts (and right and left wheels) turn simultaneously. Each wheel then rotates at the same speed.

                              However, when the vehicle makes a turn, each wheel rotates at a slightly different rpm. For instance, during a left turn, the left wheel will slow down by two rpm, and the right wheel will speed up by two rpm. One axle shaft always slows down at the exact rate that the other one speeds up. This difference in rpm is transferred to the worm wheels (because the worm gear on the axle shaft can turn the worm wheel and equalize the other side via the 1:1 spur gears, which act as balancing gears). So the engine is "Locked" or engaged on the axle shafts, while allowing for differential action when negotiating turns."
                              Last edited by pyroteck; 11-26-2009, 05:38 AM.