Lets Talk Clutches (LOJ Adapter Specifically)

In this Blog post we're going to cover a host of different topics about clutches that will better help you understand them in general, as well as understand why LOJ transmission adapters are configured with the clutch options listed.

  • Section 1 - The basics of stock single disk clutches
  • Section 2 - Hybrid Single Disk Clutches
  • Section 3 - Twin Disk Options

Section 1 - The Basics

There has been a lot of confusion and misinformation provided over the years with the differences between clutches on Nissan vehicles, specifically the Z32 300ZX (Non-Turbo and Twin Turbo), Z33 350Z (V35 Infiniti G35), 370Z (V36 Infiniti G37), and Skyline GTR (R32) models. I mention those models specifically, because all LOJ Conversions Transmission Adapters utilize one clutch form or another from these platforms. To get us started, lets cover some basics that need to be considered when speaking of these clutch differences.

The first physical characteristic, or design feature, that needs to be considered is the bolt pattern of the pressure plate to the flywheel. All of the factory clutch options for the platforms listed above use a 9-Bolt pattern with three alignment dowels, one of which is offset differently to ensure the clutch is bolted to the flywheel in the same orientation every time for balancing purposes. The flywheels and clutches that LOJ sells are neutral balanced, meaning the offset dowel is an unneccesary feature in these applications since the parts are evenly balanced in all orientations. However, older Nissan models had engines that were not neutral balanced, and weight needed to be added to the flywheel or clutch to achieve a balanced rotating assembly. This drove the need for the offset pin and that design feature has simply carried over into later models. The Non-Turbo 300ZX, 350Z, 370Z, and R32 GTR all use the same pressure plate bolt pattern. Only the Z32 300ZX Twin Turbo has a different pattern which is larger.

The second physical characteristic that needs to be considered is the physical diameter of the clutch friction surface and by association, the pressure plate and flywheel surface diameters. The Non-Turbo Z32 300ZX and R32 Skyline GTR both use a 240mm (9.45") diameter clutch disk. The Twin-Turbo 300ZX, 350Z, and 370Z all use a larger 250mm (9.85") diameter clutch disk. Why does this matter? Because in reality, clutches aren't really designed to hold a given horsepower... they're designed to hold torque loads. Horsepower is simply a function of torque at a given RPM. If you've ever tried to get a stuck bolt loose, you know that using a longer wrench gives you more leverage, and makes the bolt easier to remove. In the same vein, a larger diameter clutch can hold more torque with the same amount of clamping force applied with the pressure plate. In the early 90's, Nissan installed the larger 250mm clutch on the Z32 300ZX Twin Turbo to allow for a higher torque holding capability. They were able to maintain driver comfort by using this configuration clutch in combination with a clutch pedal that had a small booster added.

So now what do we know? For the given models mentioned above, Nissan used two different clutch bolt patterns (Pattern A "Big" and Pattern B "Small") and two different clutch disk diameters (240mm and 250mm). However it appears that in later years, Nissan figured out how to use a 250mm clutch disk diameter inside the smaller pressure plate bolt pattern, and this is the combination that has been used in all 350Z and 370Z models. They were able to get the increased torque holding capability of the larger clutch disk packaged inside the smaller and lighter pressure plate.

It is for this reason that ALL LOJ Adapter Plates for Z32, Z33, and Z34 transmissions are drilled for both pressure plates, and why LOJ exclusively offers Small Pattern 250mm clutches for our adapter kits. The small pattern pressure plates, being so common, are cheaper to produce and lighter than the large pattern pressure plates, and the 250mm clutch gives the maximum torque holding capability within that package.

Section 2 - Hybrid Single Disk Clutches

There are some adapters that LOJ produces that utilize what we call a hybrid single disk clutch. What does that mean? It really boils down to something about the clutch not 100% meeting the configuration of a stock clutch, and in LOJ's case, always referring to the input shaft spline count on the clutch disk.

This applies to our adapters for the Nissan Frontier 6-Speed Manual Transmission. For these applications, we could have used the standard 350Z clutch discussed above, and it would have worked fine. However, the Frontier transmission has a very large bellhousing compared to the 350Z transmission, and can fit a stock diameter LS1 clutch which is 12" versus the 250Z ~10". This is a huge difference in the world of clutches, and electing to use a 12" clutch will greatly increase torque holding capability without sacrificing pedal effort. 

The clutches used with all of our Frontier Transmission Adapters are the same, they are 95% an off the shelf aftermarket LS1 clutch, with the 5% difference being a Nissan spline drive in the center of the clutch disk as opposed to the standard GM spline drive. We sell Clutchmasters clutches exclusively, and threy build this specific configuration for us. However, if you have a clutch builder of choice, ANY clutch manufacturer can do this for you.

Section 3 - Twin Disk Options

The last topic to discuss are the twin disk clutch options for LOJ Adapters. In order for this section to make sense we need to discuss a few basics. First, in a perfect world a twin disk clutch would hold double the torque of its single disk counterpart given the same clamping force. Why? Because a twin disk doubles the surface area that the pressure plate applies the clamping force. In reality, this number is closer to 90% more capacity for a host of reasons beyond the scope of this article. Second, twin disk clutches are generally smaller in diameter than single disk clutches to reduce rotational inertia. Lastly, twin disk clutches utilize a unique pressure plate bolt pattern different than any OEM single disk clutch. 

That last point is the most important for us to cover in this article. Aftermarket single disk clutches like we discussed in sections 1 and 2 utilize the same pressure plate bolt pattern as their OEM equivalent. Why? Because the clutch manufacturer wants you to be able to use their clutch with your stock or any brand aftermarket flywheel out there for your application. In reality, most of these clutches utilize modified OEM pressure plates to increase the clamping force by changing the spring rates.

Aftermarket twin disks are different animals. Every manufacturer designs their own pressure plate for their applications. A Clutchmasters pressure plate is different from an Exedy pressure plate, which is different from an ACT, Quartermaster, Competition Clutch, Cusco, etc.... This is because each manufacturer develops their twin disk without the constraints of a flywheel bolt pattern. They want to use that same pressure plate for every application they can.  Additionally, a 8.5" twin disk will have a smaller pressure plate bolt pattern than a 10" single disk just because the clutch is so much smaller. 

The above reasons are the primary reason why the flywheels LOJ sells for our single disk applications are not compatible with our twin disk clutches, and vice versa. It is also why you CANNOT use another manufacturers twin disk clutch with any of our flywheels. Other manufactures bolt patters and stack heights will all vary and there is no way to make one flywheel compatible with everyone else's clutches. For that reason, if you want a twin disk clutch with an LOJ Adapter, you must use our Clutchmasters Clutch Options.

Of course, if you have any questions about the above information, feel free to contact us!!!