Four inch bore family 1996 to 2002
The 350 continued…
The Vortec 5700 L31 is a V8 truck engine and can be identified by the eighth digit in the VIN which is an “R”. The power plant is in the Cadillac Escalade, Chevy Express/Tahoe(LTD –Z71 models)/full sized pick-up, and the GMC CK/Suburban/Yukon. This 5.7 liter is the last of the first generation Chevy small block 350 engines and has proven to be the most popular. The power plant is similar to the previous LT1 version in the configuration of the heads with similar combustion chambers and intake ports but lacks the reverse flow cooling of its predecessor. This head will bolt onto earlier version blocks and can improve performance while offering a lower price tag than other options although it needs an L31 specific intake manifold with four bolts per head with other, earlier versions having six bolts to attach the manifold to the heads.
The Vortec 5700 is able to develop between 255 hp (190 kW) up to 350 hp (261 kW) at 4600 RPM and offers from 330lb-ft (447 N-m) to 350 lb-ft (475 N-m) of torque at 2800 RPM. In 2014 there is still a crate L31 being produced for marine and automobile hobbyists sold as the RamJet 350 by Volvo Penta and Mercury Marine. The last production vehicle to leave the assembly line with this engine is the 2005 is the Kodiak/Topkick heavy duty truck. The manifold from the 2014 marine version complies with automobile emission standards and is worth considering for a newer vehicle/block because it offers economy with the common type of fuel injectors used. The L31 can trace roots back to the1955 production 265 engine but is finally displaced in regular production by the 5.3 liter 350 cu in 5300 LM7 in 2002.
The 4.125 bore family 1970 to 1980
The only engine in this family is the 400 cu in (6.6 L) with the 4 inch bore (104.8 mm) and a stroke of 3.75 inches (95.3 mm). This engine differs from predecessors in that the block requires steam holes to maintain cool running temperatures as it is prone to develop hot spots in the block, head gaskets, and heads. Without these vents the engine would overheat and possibly seize up. This engine has a 2.65 inch main bearing with a 2.10 inch rod bearing journal. All other small block Chevy engines have 5.7 inch connecting rods but the 400 is unique with its 5.565 inch ones. The main journal in the 400 is a four bolt version from ’70-’72 and a two bolt style from ’73 until the end of production in 1980. This engine was never known as a high performance unit and is rated at between 245 to 265 hp for the whole of its production run. The basic equipment for all the 400 engines is a two barrel carburetor but in 1974 a four barrel version is made an option. The power plant is well known for the high torque and is used in many full sized GM and Chevy trucks including the K5 Blazer and the Jimmy including all full size ½-3/4-1 ton trucks including the larger medium duty units. Many passenger vehicles on both the “A” and the “B” body styles from inception until the 1976 model year. The block has either 2 or 3 frost plugs per side while two is normal there is provision on all blocks for a third if deemed necessary. The engine has become a standard for many racing enthusiasts in both on and off road applications.