In last month's "Tech Scene," we compared the differences between Toyota's VVTL-i (Variable Valve Timing and Lift-intelligence) and Honda's VTEC (Variable Valve Timing and lift Electronic Control). After starting the column, we realized we needed more space to fully explain the intricacies between the two engines. Although many enthusiasts have a clue of what variable valve lift is or does, many are still clueless as to how the mechanism is engaged and how it affects performance. In this article, we will cover the difference in valve lift mechanisms, cam design, intake manifolds, blocks, heads and overall performance.
Honda's DOHC VTEC
The first to enter the boxing ring is the long-standing champion: the Honda B18C DOHC VTEC engine. VTEC technology first entered the production car market in the United States in 1990, in the form of the Acura NSX engine. However, the VTEC effect dates as far back as the 1988 Honda Civic/CRX in the form of the notorious B16A, which was offered overseas at the time.
Although the NSX was the first vehicle to use the VTEC effect in a production vehicle, it wasn't until the 1992 Honda Civic Si/EX engines that VTEC made an impact in the sport compact market. Unlike the current generation B18C/B16A engine, the '92 vintage D16Z SOHC VTEC engine only incorporated the VTEC mechanism on the intake valves, improving airflow to the combustion chamber at higher engine speeds.
At the time of release, the D16Z engine produced one of the highest horsepower outputs (125 hp) of any 1.6-liter production engine found in the U.S. The D16Z engine was merely a glimpse of what was to come from Honda.
The following year (1993), Honda released the B17A engine, which made its way into the 1993 Acura GS-R. The B17A engine was almost identical to the B16A, with the exception of the displacement (1.6-liters to 1.7-liters). The two engines share a nearly identical head, intake and throttle body. Both engines also feature an 81mm bore, but had different strokes because of the difference in displacement.
The B18C made its way to our shores in 1994, powering the third-gen Acura Integra GS-R. Although sharing much of the technology of the B16A/B17A engines, the B18C was a whole new breed of DOHC VTEC. In appearance, the intake manifold was a completely redesigned unit, compared with the B16A/B17A. The major difference is the use of a dual-stage intake. At low-rpm operation, the engine ingests air from a set of long intake runners for better bottom-end torque. As engine rpm and load increase, a set of secondary butterflies open, giving the intake air access to shorter intake runners for a more direct flow into the combustion chamber, resulting in better top-end power.
By combining both the dual-stage intake and secondary cam lobes, the B18C is capable of producing power all the way to its lofty 8000-rpm redline. The use of VTEC technology revolutionized the perception of small-displacement engines. Honda was able to engineer a small-displacement engine capable of producing excellent power throughout the entire powerband, yet still pass with flying colors at the smog stations.