VTEC and Frequently Asked Questions
Q: What is VTECH?
-VTECH is a company that makes crappy phones. They have nothing to do with Honda.
Q: Oh, then what is VTEC?
-VTEC is Honda’s version of variable valve timing. It stands for Variable Valve Timing and Lift Electronic Control. It is a way of varying the lift and duration of the intake/exhaust valves in the car’s engine to maximize air/fuel flow efficiency.
Q: Ok so when does my VTEC kick in?
-The “kicking in” you’re referring to is the hi-cam profile engaging, causing an increase in power starting at a specific RPM. Since VTEC incorporates both a low-cam and hi-cam profile, it is technically ALWAYS on. To say that your VTEC kicks in, is basically a universally accepted incorrect statement. The hi-cam profile engages at varying RPMs depending on the model of Honda you drive. The D17 civic engages its hi-cam around 4300rpm.
Q: Ok, so how does VTEC work then?
-VTEC works by varying valve lift timing and duration to compensate for the time daly and out of phase arrival of the air/fuel charge at the intake valves. Ideally, in lower rpm, the valves should remain open for a short period of time, and at higher rpm, should remain open longer. This is accomplished by using twice the number of cam lobes on each cam. One set is called the low-cam profile for lower engine rpm, and the other is the hi-cam profile for higher engine rpm. (this is also why cars with types of variable valve timing rev higher than cars without) At low engine speeds, the short lift and duration of the valves are ideal for maintaining the intake charge velocity required for good engine and throttle response. At higher engine speeds, the valves must open more and for longer in order to get air/fuel into the engine fast enough. Think of it like this. At high rpm if you were to still be using the low-cam (short duration) profile, the engine would literally be gasping to breathe because it’s not getting enough air/fuel, and this would cause it to make hardly any power. Likewise, at low rpm, having the valves open too much for too long (hi-cam profile) would cause the engine to idle very rough and be extremely inefficient since you are essentially over-breathing the engine.
Q: So what does VTEC do inside my engine?
-Well, as already stated, there are 2 cam profiles on each cam. The rocker arms (or cam followers as Honda calls them) move up and down with the cam lobe profile all the time. However, at the low-rpm profile, only half of the cam followers are actually engaging the valves on the engine. (obviously these are the low-cam profile cam followers) At higher engine speeds (hi-cam engagement point) a control unit opens a spool valve sending oil pressure to pins in the cam followers. The pins low the low-speed followers to the high-speed followers, allowing the high-speed followers to engage the valves. The low-speed followers do not need to be disengaged in any way since they are simply superceded by the hi-cam followers with their greater lift and longer duration.
Q: So why does everyone say VTEC is for getting good gas mileage?
-Fuel efficiency is only half of the benefit of VTEC. If you wanted to have a car without some type of variable valve timing system, but still wanted decent power, you’d have to have a combination of both low and hi cam profiles. This would mean less fuel efficiency at lower rpm, and nearing higher rpm, the engine begins gasping to breathe. However, the low-cam profile is not only used because it is most fuel efficient. It is also used because it delivers the most power in a smooth and efficient way. Believe it or not, if you take an engine with VTEC and compare it to one without, the car with VTEC will not only make more power, but will do so across the ENTIRE rpm range. So a 1.6 liter SOHC engine will not make as much power both in low and high rpm, as a 1.6 liter SOHC VTEC engine. Same goes for DOHC. A 1.6 liter DOHC will not make as much power in both low and high rpm as a 1.6 liter DOHC VTEC. So although people say “Hondas have no torque” they are in fact, sorely mistaken. Compared to engines of the same size and configuration (SOHC/DOHC), Hondas make MORE torque than engines without a variable valve system.
Q: So what is 3 stage VTEC?
-There are varying types of VTEC. DOHC VTEC has low/hi cam profiles for both the intake AND exhaust valves. SOHC VTEC (like the D17) has only one profile for exhaust valves, but has a low/hi cam profile for the intake valves. VTEC-E works the same as SOHC VTEC, but closes off an intake valve at low RPM to allow for much greater fuel efficiency. This VTEC truly is meant for efficiency and not power gain. 3 stage VTEC exists in only one engine, the D15B. This was a civic engine available in only Europe and Japan. Just like the VTEC-E at low rpm, one intake valve is closed and the engine runs off of a low-cam profile. At the second stage, a first pin is engaged by oil pressure, opening up the closed intake valve to allow for more power like a normal SOHC VTEC. At high rpm, a second pin engages, allowing all valves to be opened by a hi-cam profile again like the SOHC VTEC. So 3 stage VTEC is a combination of VTEC-E and SOHC VTEC.
Q: Why does my friend say his Integra GS-R has 3 stage VTEC then? And I swear I can hear his engine change twice as if it has two VTECs.
-You and your friend are confusing the dual stage intake manifold in the GS-R for another VTEC cam profile. The intake manifold on a GSR has 2 sets of intake runners. One set is for lower rpm breathing, the other set for higher rpm breathing. At a specific point (BEFORE hi-cam engagement) the intake manifold closes off the longer set of runners, allowing the short intake runners to breathe better and allow a more direct flow of air into the engine. If the car has an intake, this literally will sound like the hi-cam profile kicking in, and a slight increase in power results. But then the actual hi-cam profile kicks in, and the engine really screams, now using the shorter intake runners, as well as the hi-cam profile.
Q: So if VTEC is so great, why doesn’t everyone have some sort of VTEC-like system?
-There are a fair amount of manufacturers that DO have a variable valve timing system. BMW uses VANOS, Honda uses VTEC, Toyota uses VVTI, and even FORD (yes ford) uses variable cam timing. FORD’s first engine to do this is the 5.4 liter modular V8 triton engine that powers the Ford F150. Why is Ford using it? “The new 24-valve engine will be our first modular V-8 to use variable-cam timing. This design allows Ford engineers to optimize intake-and exhaust-valve actuation across the rev range.” So in other words, they’re using it for the same reason Honda and everyone else does. Keep that in mind next time some Ford guy is telling you how Honda’s VTEC is stupid. Ford is using the exact same technology in one of their own engines now. About time American car manufacturers caught on.
Q: When was VTEC first introduced?
-That depends on where you mean. Japan got VTEC in 1988 (model year 1989) by way of an Integra. The US first saw VTEC in 1990 by way of the NSX.