This custom flex plate kit is designed to adapt the Gen III / LS series to the GM TH400 transmissions. The kit includes a flexplate, 11mm flex plate bolts, crank spacer.
Gen III / LS Engines
The new style Gen III / LS series engines (4.8, 5.3, 5.7 LS1, 6.0, 6.2) all have the same crank stick out which is .400” closer to the block than the traditional 350 V8. The Gen III / LS series crank bolt pattern is different than any other GM crank as to the bolt pattern on the flex plate. Only Gen III / LS series flexplates fit these engines!!!
Since a Gen III / LS series flexplate only fits a Gen III / LS series and the engine crank is recessed .400”. There are a few unique things about the torque converters that bolt to the flexplate. The spacing of the flexplate from the back of the block is the same as early GM blocks. The flexplate is dished out .400” to compensate for the crank. The differences come into play as to the bolt pattern of the torque converter to the flexplate and the snout length of the torque converter.
How do we adapt TH400 to a Gen III / LS series engine? We offer a custom flexplate to fit a TH400 and a crank spacer that compensates for the shorter engine crank.
NOTE: This kit includes a new flexplate and it may not work on all LS series engines. The 6.0L engine with cast iron cylinder heads should only be used with the original transmission due to a different crank shaft stick-out length. It does not have a recessed crank. The 4.8L engine coupled only to a manual transmission in 1999-2003 does not have a recessed crank.
LS7 / LS9 / LSA / LSX engines all have a 8 bolt crank that hold the flexplate do the engine. This kit is not cannot be used.
Note: This kit will not fit 2014 & up Gen V engines (New LT1 V8 & 4.3 V6, 5.3, 6.2)
The GM Generation III & IV blocks are classified as a 4.8L, 5.3L, 5.7L(LS1), and 6.0L. These blocks have gained popularity because of the emission controls required when performing a engine swap. A few things to consider when using a Generation III V8 block are as follows: All fasteners are metric. The heads of a Gen III are wider than an early GM V8, so the exhaust manifolds are tough to fit between the frame rails on most vehicles. The exhaust on the driver’s side can be a problem for mechanical clutch linkages. The oil pan is aluminum and cannot be modified. This can cause some problems on vehicles requiring oil pan modifications. We recommend the installation of a Gen III into the following vehicles: Jeep TJ, YJ, and CJ7 (CJs may be required to use a header system), Toyota Land Cruiser, full size Chevys, and any other vehicle with a minimum of a 25” inside frame width.
Transmission Combinations: The Gen III engines have the same block bolt pattern as the early GM with the exception of one bolt hole. When bolting an earlier GM transmission or one of our bellhousings to the Gen III block, you will only be able to use 5 bolts on some bellhousing kits. The Gen III engine used a different crank stickout from the back of the block and a different crank bolt pattern. This means the early style flywheels and flexplates will not bolt to the new Gen III blocks. The stock flywheels and flexplates from the Gen III blocks are also unique with regard to the clutch bolt pattern and the torque converter bolt pattern. We have designed two kits for either a manual transmission or an automatic.
There are some Gen III blocks that do not have the recessed crank. This kit will not work on these blocks. One block that we know of is the 6.0L with cast iron heads and the 4.8 or 6.0 engines coupled only to a stock manual transmission in 1999 to 2003. A custom flywheel would have to be made to work on these block P/N CF720000.
The kit designed to fit a manual transmission is PN712500M (Luk Clutch) or PN712500M-CF (Centerforce clutch). This kit includes a flywheel, flywheel bolts, 11” pressure plate & disc, bolts for the pressure plate, pilot bushing spacer, release bearing, and metric bolts & washers for the bellhousing. The above listed kit works with our bellhousing kits P/N 712525, 712548, 712549, 712567V 712576, 712577, and 712591V. A special starter, P/N 22-0002, is required if using bellhousings 712567V and 712591V 716155 GEN III BUSHING & 716154 GM
The kit designed to fit the TH350 or 700R automatic transmission is PN712500A; and for the TH400 transmission PN712500A4. These kits include a modified flexplate (drilled for a early GM torque converter), flexplate bolts, crank spacer bushing.
Exhaust: The truck manifolds fit the majority of applications with the exception of the Jeep CJ. The Jeep CJ can use a Gen III Camaro manifold or exhaust headers that we manufacture. On our NV4500 bellhousing kits, the truck manifolds also have some clearance issues with the slave cylinder. We sell a slave cylinder bracket for a NV4500 and Gen III engine application. We also offer a rear dump header similar to truck manifolds, P/N 717045. PN717040 Jeep CJ Gen III Fenderwell Header PN717043 Gen III Center Dump Header PN716286 Slave Cyl. Brkt. (NV4500 w/ truck manifolds)
Vacuum Lines: You will notice that the GEn III block has no provision for vacuum lines. There is a small port on the back of the intake manifold that can be used. First, pull out the black plug on the intake manifold by holding pressure on the gray ring. Once the plug is out, drill and tap the black plug for a 1/8” pipe thread. Use a 90 degree 1/8” pipe by 3/8” barb adapter and thread it into the tapped plug. Press the plug back into the manifold and attach the hose.
Radiators: The Gen III requires a steam release port which is a standard feature on our radiators that the part number ends with a (-LS) at the end. The Gen III also require smaller water inlets and outlets on the radiators. The Gen III engines recommend a 50/50 mixture of Dex-cool and water.
Fan: We recommend using an electric fan in most installations. Our Spal fans allow for ample clearance in the engine compartment providing for good air circulation. We offer a Spal fan kit (to fit our radiator) under P/N 716670. This fan is rated at 2070 CFM.
Wiring: Installing the Gen III is fairly simple; however, depending on the year of the vehicle, coupling to the stock gauges may require a vehicle service manual. For example, on a Jeep TJ we retained the stock Jeep sending units and attached them to the GM block (oil pressure, temperature, and fuel level). All of them work fine except the tachometer (in which we installed an aftermarket one). Since we used the stock sending units and because the Jeep TJ had a computer controlled stock engine, the Jeep computer thinks that the original engine is still sending information. Vehicles that were not originally computer controlled may just need new dash gauges coupled to the Gen III sending units.
Throttle Linkage: The throttle cable that comes on most Gen III engines has a standard cable connection which can be fitted to most gas pedals. A new, larger access hole may need to be drilled in the firewall where the stock cable was originally located.
Fuel: The Gen. III fuel rails have anywhere between 50-60 pounds of fuel pressure! Only approved high pressure hose and fittings should be used. The Gen III engines need a minimum diameter of 3/8” line on the pressure side, and a minimum of 5/16” on the return side (3/8” is best for the return line). Depending on the year, model, and make of your vehicle, you will need to find out what type of fuel delivery system your vehicle was equipped with and what type of pressure it was running. For example, a Jeep TJ used a fuel pump that was internally regulated in the fuel tank at 46 psi. Since the Jeep regulated the pressure at the tank, it did not run a return fuel line. On this installation, we opted to run two new 3/8” lines; one pressure and one return. The pressure line needed to be installed by drilling and installing a bulkhead-type “AN” fitting alongside the stock Jeep pump assembly. A fuel tank pickup also had to be installed. The old “pressure” line out of the Jeep tank was used as a return line from the Vortec. To use this connection, we had to remove the stock internal regulator. This is just an example of one application we encountered.
The Gen III crank is almost flush with the back of the block