Honda Acura NSX 1991, Service Manual

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general, it would be ideal if the high rpm performance of a racing engine and the low rpm performance of a standard
passenger car engine could be combined in a single engine. This would result in a maximum performance engine with a
wide power band. Two of the major differences between racing engines and standard engines are the timing of the in-
take/exhaust valves and the degree of valve lift. Racing engines have longer intake/exhaust timing and a higher valve lift
than standard engines. The Honda Variable Valve Timing and Lift Electronic Control System takes this into
account.
When valve actuation is adjusted for low rpm timing and lift, low rpm torque is better than in a standard engine. When
valve actuation is then adjusted for high rpm timing and lift, output improves to the level that a racing engine can offer.
Until now, few variable valve timing systems have been commercialized. In those that have, only the time that both
valves are open (intake/exhaust overlap) could be changed. Honda’s system is the first in the world in which both the
valve timing and the degree of valve lift can be changed as needed, making it the most advanced valve train mechanism
available.
Comparison of Valve Lift of Racing Engines vs. Mass Produced Engines
Racing Engine
Variable Timing
Lift Engine
Standard Engine
Valve Timing
Valve Lift
Exhaust
Intake
Exhaust Intake Exhaust
Intake
Max. Power 0 0
Low rpm Torque 0 0
idling Stability 0 0
*TDC = Top Dead Center *BDC = Bottom Dead Center
0 = Optimum Characteristic
The engine is equipped with valve timing and lift settings which change according to driving conditions.
Low rpm
H i g h r p m
Variable valve timing
and
Lift
engine
RPM
switch over
point