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GM Generation III & IV Conversion Flywheel

In 1997, with the introduction of the groundbreaking LS / Vortec series engines, GM changed the depth of their crank flanges by about 3/8" under their previous and Chevrolet crank specifications that had remained their standard since at least 1955. With this, they also changed to a newer style of clutch system whose height, spline count and release ratios changed from the popular and more affordable clutch assemblies that dominate the OEM and aftermarket.

Product & Features


A very key piece of Novak's recipe for successful Gen. III & IV engine conversions with standard shift transmissions is this flywheel, featuring the following:

  • Spaces the entire clutch assembly rearward; closer to the clutch release "throwout" bearing for more effective clutch release
  • Provides for maximum transmission input shaft spline engagement
  • Made of billet steel
  • Places the ring gear in the proper plane of its starter motor
  • Compatible with the earlier, standardized GM / Chevrolet 12" clutch kits
  • Precision balanced
  • SFI explosion-proof rated
  • Uses the far more predominant OEM bolts as are used with the GM automatic flexplates
  • Moderate 35# weight for a great balance between sustained torque and quick revving
  • 168 tooth ring gear


One beautifully machined billet flywheel.

Applications & Compatibility


The LS400-35X flywheel is compatible with most Generation III & IV GM V8 engines, including the 4.8L, 5.3L, 5.7L, 6.0L, 6.2L engines in conversion scenarios. This flywheel is not compatible with the GM 4.3L V6 or Atlas series engines.

There are several exceptions to this rule for which you must watched out. Some 4.8L & 6.0L engines from 3/4+ ton truck applications have a crank face in the standard Gen I position but with the LS bolt pattern. Please refer to this page for more information on these applications


Compatible transmission combinations include (adaptation may be required):

  • SM465
  • SM420
  • NP435*
  • Ford T18 / T19*
  • Jeep T90
  • Jeep T98 (M715)
  • Jeep T18*
  • Jeep T14 / T15
  • T150*
  • T176
  • AX15
  • NV3550
  • NSG370

*Special combination clutch kit required for 1-1/16" input splines

Advantages Over Factory Flywheels 

Prior to the Gen. III, GM conversion engines (Gen. I-II) were generally always able to use a factory flywheel. The manual transmission is virtually extinct from the line-up of GM trucks and most cars now. The famous 5.3L Vortec has never been available with a manual transmission option. Only the 4.8L and 6.0L Vortecs featured manual transmission options and therefore a factory flywheel, whose neutral balance does match the 5.3L and other Gen. III+ engines.

At Novak, we strive to use factory style parts to the maximum extent possible, and both we and our customers have tried many things to make these factory flywheels somehow work, without much real success. We are often asked why they don't and can't be made to properly work in conversion scenarios. The following are the main reasons why the use of these OEM flywheels are incompatible in conversion situations:

  • They cannot be spaced rearward without taking the ring gear out of the plane of the starter's drive gear
  • Any compatible pressure plates have a unique bolt pattern and problematic release ratio with Jeep and earlier GM mechanical and hydraulic release systems
  • They don't fully engage the splines of conversion transmissions
  • Most available clutch disc hub spline counts are incompatible with the myriad conversion transmissions that feature the 10 x 1-1/8" input shaft splines
  • Lower clutch disc surface area
  • Additionally, these newer clutch assemblies remain quite expensive over their classic counterparts, by usually 35% or more

See this page for additional information

Related Products

Flywheel bolts

We recommend and offer ARP's 12-point alloy flywheel bolts for this application


Adjustable Release Bearing

While sometimes not needed in this application, Novak's unique and adjustable throwout bearing assures the right height of bearing, which is the most important factor in any clutch system's successful operation. 


We frequently reach for this adjustable bellhousing arm pivot, which adds additional adjustability and better release arm angles. 


Installation Requirements

Installation requires use of the six OEM automatic flexplate-to-crank bolts. A torque wrench is required and the recommended torqe of the bolts be set to 74 ft. lbs. in three successive stages - 15 ft. lbs, 37 ft. lbs. then 74 ft. lbs. Use of a removable thread locking compound (such as LocTite™ Blue) is recommended if your bolts are not already pre-coated with the factory applied locking compound.

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