GM Gen III Vortec

The GM Vortec Generation III 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 Vortec Generation III V8 block are as follows: All fasteners are metric. The heads of a Vortec 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 Vortec 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 Vortec 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 Vortec block, you will only be able to use 5 bolts on some bellhousing kits. The Vortec 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 Vortec blocks. The stock flywheels and flexplates from the Vortec 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 Vortec 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 6242-002.

The kit designed to fit a manual transmission is PN712500M. 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  

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. Transmissions such as the 700R4 will require a TV cable kit, PN718000. Transmissions like the TH350 and TH400 will require a Lokar kickdown cable.

Exhaust: The truck manifolds fit the majority of applications with the exception of the Jeep CJ. The Jeep CJ can use a Vortec 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 Vortec engine application. We also offer a rear dump header similar to truck manifolds, P/N 717045. PN717040 Jeep CJ Vortec Fenderwell Header PN717043 Vortec Center Dump Header PN716286 Slave Cyl. Brkt. (NV4500 w/ truck manifolds)

Vacuum Lines: You will notice that the Vortec 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 Vortec 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 Vortec 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 Vortec 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 Vortec sending units.

Throttle Linkage: The throttle cable that comes on most Vortec 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 Vortec Gen. III fuel rails have anywhere between 50-60 pounds of fuel pressure! Only approved high pressure hose and fittings should be used. The Vortec 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