VTEC and its many iterations.
Ok, so a lot of people don't really understand the many different forms of VTEC much less what it is or how it works. Anyway, I don't feel like explaining how it really works, but here are the million different forms of VTEC.
SOHC VTEC.
This is the general, run of the mill VTEC that we see in most Honduhs (Civic Si, 4 bangin Accords..). Basically, the VTEC concept is applied to the intake side of things. We reach the VTEC engagement point and BAM, oil pressure forces a little pin to engage the wild profile lobe. This VTEC is the shiet. It basically gives you DOHC performance from a SOHC engine.
VTEC-E.
The E stands for Economy. In this version of VTEC, there is actually only one cam-profile, and VTEC has nothing to do with cam-profile optimization. What happens is that at low rpms, one of the intake valves is inactive, so the combustion chamber is only running on 3 valves. Basically, this is designed to put a funky swirl on the AF mixture so that it burns more thoroughly. At higher RPMs, VTEC is used to activate the 2nd intake valve so that the engine can operate normally. With VTEC-E, you actually lose a bit of power compared to non-VTEC models.
3 STAGE VTEC.
Basically, the Honduh guys decided to combine SOHC VTEC and VTEC-E. This involves using two VTEC systems on the same engine and one activates after another to give three stages.
Stage 1-combustion chamber is on the passive lobe with 3 valves.
Stage 2-combustion chamber is on the passive lobe with 4 valves.
Stage 3-combustion chamber is on the aggressive lobe with 4 valves.
As far as I know, 3 stage VTEC is only being used on the 1.5L engine in the Ferio.
*some people seem to think that this is superior to DOHC VTEC, because DOHC VTEC is 2 stage, which is incorrect. Don't forget that 3 stage VTEC is only VTEC-E and SOHC VTEC working together.
DOHC VTEC
The Holy Grail of VTEC. VTEC technology is implemented on both the intake and the exhaust cams. Basically this is Honda's best form of VTEC, and it is purely intended for performance, not economy. You see this in Honda's performance cars (NSX, Prelude, SiR, etc)
iVTEC
This comes in SOHC and DOHC forms on a variety of Honda's new K series engines. Basically the i implies that VTEC is now supplemented with infinitely variable camshaft phasing, which continuously changes the camshaft timing depending on RPM, engine load, etc for optimum output. iVTEC is something that Honda really needs, because everyone always complains about how Honda's have no torque...but with iVTEC, you get tons of low-end torque.
Whew ok, I think I got it all...
edit:
VTECH
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