Civic VX, VTEC-E, D15Z1, etc

[suspendedhatch]

I thought I'd post up some diagrams to help clarify things and also to make them available for anyone else that wants to copy them into other threads etc. I hope that this thread will make things clearer to people and to help dispel some false assumptions and misconceptions that people make when they have only a partial understanding of VTEC-E.

This thread is wide open for any VX fanatics to contribute to in any way whether it's posting up info or simply posting a link. I'm not claiming ownership, I'm just kicking this off. MY ONLY REQUEST IS TO KEEP EVERYTHING IN LAYMAN'S TERMS.

VTEC-E is very simply explained as a method of switching from 12 valves to 16 valves on a 4 cylinder engine. One intake valve per cylinder is closed under certain conditions in order to improve low end torque and decrease fuel consumption. Then when load and RPM have increased, both intake valves open up to allow more air so that the engine doesn't choke up; giving you better mid range power. The cam lobes are optimized for BOTH low and mid range.

Normally no power is sent to the VTEC solenoid resulting in 12 valve mode. When RPM conditions are met, the VTEC solenoid is energized resulting in 16 valve mode. In other words, when the solenoid is ON, VTEC-E is OFF.


Here's a diagram of the D15Z1. Not very educational but very interesting to look at. The most obvious difference between this and its contemporary D-series motors is that the catalytic converter is mounted directly to the exhaust ports to light it off faster and decrease emissions.


This is a good demonstration of how closing one intake valve per cylinder swirls the incoming air into the combustion chamber in order to spread the fuel evenly for a complete and uniform burn. This is how it is possible to run a very lean mixture which would cause a lean misfire in conventional engines, even the very closely related D series engines from the same time period.



Notice that "lean burn" occurs in the very low load (high vacuum / low pressure) portion of the fuel map. There is a wide range of driving where you're in 12 Valve mode but not lean burn.


Here is the SOHC VTEC description (D16Z6) for comparison purposes. Though the switching mechanism for VTEC is exactly the same as that for VTEC-E, using the same parts and wiring, the purpose behind these two technologies is different. Honda just happened to have this particular switching apparatus available and in production at the time. But don't make the mistake that you can simply put an Si/EX ECU into a VX and it's converted to VTEC. The cam and valve train are fundamentally different.


VTEC by comparison optimizes both mid and high range RPM power combining racing cam lobes and daily driving cam lobes so that you not only have impressive high RPM power, but a smooth steady idle, low emissions output, and low fuel consumption.