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.
Toyota's DOHC VVTL-I
Toyota's first variable valve timing with intelligence system, dubbed VVT-i, first appeared on the road in the Lexus GS/LS/SC 300/400 in 1998. The addition of variable valve timing made it possible to control intake valve timing for optimal performance. VVT-i can be seen as a high-tech adjustable cam sprocket. Unlike conventional adjustable cam sprockets, which have to be set prior to starting the engine, the VVT-i is an on-the-fly proposition.
The VVT-i system uses engine speed, intake air volume, throttle position and water temperature to calculate optimal cam timing. The ECU can advance or retard the intake cam depending on light, medium or heavy load, optimizing output throughout the entire powerband. Like Honda's VTEC technology, Toyota's VVT-i system was already incorporated in Japan for a period prior to its introduction into the U.S. automobile arena.
The system was taken one step further in 2000, by incorporating a changeover mechanism, which varies the amount of lift seen by the intake and exhaust valves while the engine is operating at high speeds. The new VVTL-i system first debuted in the Toyota Celica GT-S (2ZZ-GE engine). By joining the innovative VVT-i system with variable lift, the 2ZZ-GE powerplant produces a very broad powerband.
Variable Lift Activation
There are certain variables that have to come into play before the VTEC and VVTL-i system are activated. The Honda B18C VTEC engine requires the right rpm input, water temperature, throttle position signal, oil pressure signal and vehicle speed sensor reading before the VTEC system is engaged. If any one of the five variables is out of sync or not functioning, the system will not engage.
Toyota's VVTL-i system is far less complicated and only requires water temperature, crankshaft position sensor and engine rpm before the lift mechanism is activated.
The B18C VTEC changeover point is a surprisingly low 4400 rpm compared with Toyota's 6000-rpm changeover point.
Valve Lift Mechanism and Cam Design
Both Honda's VTEC and Toyota's VVTL-i utilize oil pressure to activate a locking mechanism to achieve higher valve lift. However, the two manufacturers achieve this from two different avenues. The major difference can be found in the cams.
The B18C VTEC cams utilize a total of 24 lobes (12 on the intake side and 12 on the exhaust side). The 16 primary lobes are directly on top of the 16 valves. The other eight VTEC lobes, which are sandwiched between the primary lobes (one for every two primary lobes) are positioned between the two valves (see photo A). As the VTEC motion assembly is locked in position, it only requires one VTEC lobe to actuate both valves.
The 2ZZ-GE VVTL-i cams only utilize a total of 16 lobes (8 on the intake and 8 on the exhaust). Unlike the VTEC system however, which requires 16 lobes to actuate the primary 16 valves. The VVTL-i system only requires eight lobes. This is made possible by a linked rocker arm assembly (see figure B). At any given time, the rocker arm assembly is being actuated by only one cam lobe per every two valves. The VVTL-i system reduces the need for a third rocker arm assembly like the VTEC counterpart, reducing weight from the motion assembly.
As any performance enthusiasts who have seen the variable lift assembly firsthand know, Honda's VTEC motion assembly is held in place by two rocker shafts (one on the intake side and one for exhaust side), which run the complete length of the head. When conditions are ideal, an oil control valve (VTEC solenoid) on the distributor side opens and allows oil fluid to fill the rocker shaft. The rocker shaft provides the necessary oil fluid pressure needed to lock the third rocker arm in place-and voila! VTEC is achieved.
In a manner similar to the VTEC system activation, the VVTL-i also utilizes two-rocker shafts to supply oil to the lift mechanism. Since the VVTL-i system only utilizes one lobe for every two valves, a rocker arm pin is locked in place with oil pressure under the high-speed cam (see figure C). When the rocker arm pin is locked in place, higher lift and duration is achieved from the high-speed cam.
As stated earlier, the B18C engine incorporates a dual-stage intake. The dual-stage manifold on the B18C engine features two intake runners for each cylinder, one longer than the other. When engine speeds are under 5800 rpm, only the longer runners on the intake are being utilized. When engine speeds pass 5800 rpm, a secondary butterfly valve within the intake opens allowing passage through a set of shorter runners (see figure D).
On the other side, the 2ZZ-GE intake is constructed from a combination of aluminum pipe runners with an aluminum die-cast intake plenum welded together for weight reduction. The reverse plenum design and equal length runners ensure all cylinders are receiving the same amount of air, increasing volumetric efficiency among all four cylinders (see figure E).
Both the B18C head and 2ZZ-GE head are constructed from cast aluminum. The DOHC design of the B18C and 2ZZ-GE head also incorporates a high intake port angle, increasing airflow into the combustion chamber. The B18C head is considerably larger and heavier than the 2ZZ-GE, partly because of the large three-rocker motion assembly. Although the head casting of the 2ZZ-GE is rather narrow in width, a cross section of the head (see figure F) shows a steep 43-degree valve angle for improved intake and exhaust flow efficiency.
Since the early '80s, Honda has been notorious for using a floating sleeve (open deck) design for its engine blocks. The floating sleeve design promotes heat dissipation to the cooling jackets surrounding the cylinder walls, decreasing chances of detonation caused from extreme heat saturation. The cast aluminum block features cast-iron cylinder sleeves, preventing cylinder distortion and is outfitted with an oil jet cooling system, ensuring long-term durability and reliability. An oil jet under each piston sends pressurized engine oil to the underside of the piston to help dissipate the heat caused by sustained high-rpm operation.
Toyota's 2ZZ-GE block also features an open deck design, which is a new concept for Toyota. Unlike the company's traditional cast-iron, closed-deck blocks, the 2ZZ-GE block is constructed from cast aluminum, which enhances weight reduction on the weight-conscious Celica GT-S. The cylinder walls are made of a metal matrix composite to ensure wear resistance.
Who is the undisputed champion of small-displacement, high-output engines? By just checking out the manufacturers ratings, the 2ZZ-GE engine has a clear advantage on horsepower output; 180 hp for the 2ZZ-GE and 170 for the B18C. The 2ZZ-GE engine also has a slight advantage with a torque rating of 133 lb-ft compared with 128 lb-ft. What better way to decide then to take it to the dyno? The two testers we used were a 2000 Celica GT-S with 5,000 miles on the odometer and a 1994 Acura GS-R with 62,000 miles on the odometer. The reason for the 1994 model GS-R and not the 2000 model GS-R was due to OBD-II. We have found out from extensive dyno tuning sessions with GS-Rs that the 2000 model GS-R produces far lower base numbers than the non-OBD-II GS-R.
In the dyno cell, testing clearly showed the GT-S producing considerably more overall peak power than the GS-R. But what surprised us was how the GS-R was able to produce substantially more power on the bottom-end (before 6400 rpm) than the GT-S. For all-out performance, we have to give the nod to the GT-S, but for overall usable horsepower, we pat the GS-R on the back.
Is there a new champion in the ring? Well, not really. Although the two engines have fought to a draw, we have to give the split decision to the GS-R, because of its unmatched aftermarket support. However, given some time to build a strong tuner following, we wouldn't be surprised to see the 2ZZ-GE taking the title in the near future.
|TALE OF THE TAPE|
|Cylinders & Arrangement||4-cylinder, In-line||4-cylinder, In-line|
|Valve Mechanism||16-valve DOHC Chain Drive||16-valve DOHC Belt Drive|
|Combustion Chamber||Pentroof Type||Pentroof Type|
|Displacement||1796cc (109.6 cu.in.)||1797cc (110 cu.in.)|
|Bore x Stroke||82.0mm x 85.0mm||81mm x 87.2mm|
|Max Ouput||180 horsepower (7600rpm)||170 horsepower (7600rpm)|
|Max Torque||133 lb-ft. (6800rpm)||128 lbs-ft. (6200rpm)|
|Redline||8000 rpm||8000 rpm|