How Honda's V-TEC makes it's power

In any engine, the only way to make more power is More Air and More Fuel. The easy part is getting the fuel. You simply use larger injectors, work the injectors harder (not recommended) or increase the number of injectors. The tricky part is to get the air in. To do this you either use some sort of device to compress the air and literally ram it through the inlet ports ala turbo charging/supercharging or you can try and increase the breathing performance and efficiency. Now to increase the breathing efficiency you can do one of those things or all which is what most people normally do. This includes: 1. Increasing the port shape and size so that more air flows in without losing the velocity. As you know Bernoulli's Principle states that if you increase the area you lose the velocity but there are "tricks" which can be employed to juggle between both. 2. You increase the cam duration and lift. The longer the valves are opened and lifted the more the air can flow in. Unfortunately this area is again a compromise. A naturally aspirated engine that has big cam duration and lifts still needs the vacuum in the engine to draw the air in. And as stated earlier, having the ports open sooner and more valve lift is the equivalent to increasing the air and you lose the velocity. The engine then struggles to breathe at low revs and occasionally loses one of its power strokes due to this efficiency. This phenomenon is called eight stroking and leads to that V8 like idle and poor low-end performance. It also leads to an over rich condition and generally leads to lots of bad exhaust emissions. This problem is not an issue once there's an increase in revs and the efficiency of the engine is enough to match the camshaft characteristics. So some bloke in Honda must have though "Heck, why can't I have the BEST of both worlds. I have a cam lobe profile that gives an excellent idle and good exhaust emission at low revs plus another cam lobe profile that will give me good breathing efficiency at high revs. Also, let's include an intermediate profile for excellent air swirl to further increase the airflow into the engine. While we're at it let's design a rocker mechanism that is operated using oil pressure via a solenoid to switch between the low and high cam profiles at a preset rpm. Let's control all this via the ECU. This is what VTEC is. But remember, 1 & 2 are still interlinked. So Honda juggled between the best of both areas and came up with the very first B series engines 10 years ago. Now let's go back to 2. First. There are many ways to open and close the cams and most road engines usually use a mechanism called a hydraulic lifter or followers. The advantage of this mechanism is it's quiet and doesn't need frequent and labour intensive adjustment like a solid lifter engine. Unfortunately there is a downside to the hydraulic lifter. They don't like long duration and lift. Hydraulic lifters can suffer from three main maladies: - i) Pumping up, where the lifter solidifies too early during the lift ramp of the cam and over-lifts the valve, this can happen when an engine is over-revved. But you can control this with a reasonable rev limit. ii) Pumping-out where oil is evacuated from the lifter causing the lifter to solidify too late in the lifting ramp and the valve is under-lifted mainly caused by too fast a lift or too wide a duration. iii) Oil aeration which allows the hydraulic lifter to be compressed rather than solidifying on lift, this is the main cause of valve train rattle. Of these i) is the most dangerous since it can lead to valve/piston contact, ii) and iii) just cause the engine to rattle and subject the lifter/follower and cam to shock loads which should have been absorbed by the take up ramp designed into the cam profile. All in all hydraulic lifters and aggressive cam profiles are not too a happy combination. Needless to say Honda VTECS don't use this but the 4G93P does So now that we know, what else makes the B series or the B18C such a good engine? These are: 1. Good port shapes and flow of the engine. The B18C straight out of the box flows an amazing 141+ cfm with no loss when the throttle body and inlet manifold are fitted compared to the 4G93 at around 120+cfm. 2. VTEC enables you to use wild cam profiles. Honda merely specified more lift and duration for the Type R spec. A stock 4G93 has about 256 degrees duration vs. 280+ for VTECS. The B18C is also capable of 11.5mm inlet valve lift and 10.5mm exhaust valve lift, which is simply amazing. The 4G93 is quite good for a hydraulic lifter but pathetic compared to a B18C at around 8+mm of lift. 3. When you use big cam profiles you usually lose dynamic compression (when the engine is working). Now as you know compression is yet another power tool. General theory states that for every 1 point increase in compression you'll get about 3-4% more power. Reason is the valves are open for such a long length of time and generally overlap a lot too (both inlet and exhaust are opened at the same time) that you lose compression. So to resolve this, Honda specified what a very high static compression of 11.1 for the B18C. The 4G93 is only around 10.5 but closer to 10.0 By now you can clearly see that in stock form as far as power output and capabilities are concerned the B18C has all the right "parts" compared to a more road oriented engine like the 4G93P. However all is not lost. You can make the 4G93P perform like a B18C by: 1. Having more static compression 2. Increase cam duration and lift. But you must be asking what about the fact that hydraulic valvetrain hates big cam profiles. There are of course tricks to get around such a thing for which it'll take me even more time than what I have to explain. Maybe part 2? The idle will be poor and lumpy though due to the event I explain earlier. Emissions? What emissions? Most petrol heads I know of can live with that. Oh and don't forget to increase the revs too. 3. Port the engine in such a way that the 4G93 flows as well as a B18C. This is not an issue so long as you have a Serdi, good skills, knowledge and experience and a flow bench to measure your work. The Rover K series engine is of very similar configuration and capacity to a 4G93 except that it is lighter having an all aluminium head and block. It uses hydraulic valve train too. There is no VTEC but there is VVC for the more performance-oriented variants that is simply dynamic cam timing control. Now consider this, how on earth did many tuners extract 220 to 240+ bhp onwards from that engine without using VVC for road use? I'll explain that in part 2 if I have the time. Might have missed some parts or intricacies in this very long posting which I might have overlooked or forgot and for which I apologize but this is generally the gist. Enough blabbering._________________