Engines for Offroad Applications

Chevrolet 4.3L V-6 Data

The Vortec 4300 is a 90° V6 truck engine, replacing the Chevrolet 250 in light trucks and 200/229 90 degree V6s in passenger cars (the 200 and 229 were known as the V6-90, both were shortened versions of the Small Block Chevrolet). It is based on the 350 in³ (5.7 L) Chevrolet small-block V8.   

All Vortec 4300s use a cast iron block and heads and 101.60 mm (4.000") bore and 88.39 mm (3.48") stroke (bore and stroke dimensions the same as a 350). Connecting rods still measure 5.7" although the rod journal diameter is 2.25".

1992-present cylinder blocks used a different timing cover since these engines used a balance shaft (some 1992 production cylinder blocks for the LB4 with TBI induction used the 'traditional' front timing chain cover from the small block Chevrolet). They are OHV engines with two valves per cylinder

Weight: approx: 450 Lbs

Produced in: Tonawanda, New York and Romulus, Michigan.

Throttle body injection:   4.3L LB4

The engine first appeared in 1985 with the throttle-body injected LB4 in passenger cars (light trucks and vans had carburetors until 1987). In 1991, the limited-edition GMC Syclone featured a 280 hp and 360 ft•lbf turbocharged/intercooled LB4 with the first use of multi-port fuel injection on a Vortec V6.

Throttle-body injection (called TBI by General Motors and Central Fuel Injection (CFI) by Ford) or single-point injection was introduced in the mid-1980s as a transition technology toward individual port injection. The TBI system injects fuel at the throttle body (the same location where a carburetor introduced fuel). The induction mixture passes through the intake runners like a carburetor system, and is thus labeled a "wet manifold system". The justification for the TBI/CFI phase was low cost. Many of the carburetor's supporting components could be reused such as the air cleaner, intake manifold, and fuel line routing. This postponed the redesign and tooling costs of these components. Most of these components were later redesigned for the next phase of fuel injection's evolution, which is individual port injection, commonly known as MPFI or "multi-point injection". TBI was used extensively on American-made passenger cars and light trucks in the 1980 to 1995 timeframe.

Central port injection (CPI):  4.3L L35 and 4.3L LF6

The central-port injected L35 (Vin 'W') debuted in 1992 (where the cylinder block was modified - with the incorporation of a balance shaft), with better breathing for 200 hp (150 kW). Another CPI engine, the LF6, joined the rest in 1996, while the LB4 was retired after 1998.

General Motors developed an "in-between" technique called "central port injection" (CPI) or "central port fuel injection" (CPFI). It uses tubes with poppet valves from a central injector to spray fuel at each intake port rather than the central throttle-body. This system tends to have a high failure rate and repair is fairly easy. The 2 models used were CPFI from 1992 to 1995, and CSFI from 1996 and on. On early CPI (CPFI) systems fuel is continuously injected to all ports simultaneously also called "batch fire", which is less than optimal. On 1996 and later CSFI systems the fuel is sprayed sequentially as the name implies "Centralized Sequential Fuel Injection".

Multi-point fuel injection: 4.3L LU3 and 4.3L LG3

In 2002, GM introduced a new multi-port injected LU3 engine, and a LG3 variant appeared soon after.

 Power output of the new LU3/LG3 engines is 180-200 hp (134-150 kW) and 245-260 ft•lbf (332-353 N•m).

Multi-point fuel injection injects fuel into the intake port just upstream of the cylinder's intake valve, rather than at a central point within an intake manifold, referred to as SPFI, or single point fuel injection. MPFI (or just MPI) systems can be sequential, in which injection is timed to coincide with each cylinder's intake stroke, batched, in which fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke, or Simultaneous, in which fuel is injected at the same time to all the cylinders.

All modern EFI systems utilize sequential MPFI. Some Toyotas and other Japanese cars from the 1970s to the early 1990s used an application of Bosch's multipoint L-Jetronic system manufactured under license by DENSO.

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