Ok before I start, I haven't really researched it too much but I guess I unnderstand the basic concept of Vtec.

My friend was trrying to explain how Ivtec was a little bit better than Vtec, which I agreed, but his explanation was a little vague. He just said it makes the valves open faster...

I'm guessing but with regular vtec the soleniod activates it and oil pressure causes the cam to change for more duration and lift? So what exactly does the Ivtec do?

Please excuse my n00bness...just trying to understand..

 

www.howstuffworks.com :goodjob:

 

bah, beat me to it. exactly what i was gonna post too.

 

Thank you.

 

I have always found the hi-po vtec and Ivtec engines dont really "work" that well, there is always a notable and quite nasty hesitation / flat spot at 6000 rpm when the cam profile changes. yuk.

 

VTEC works by allowing you to have 2 different cam profiles on 1 cam. One that idles right and gives good low rpms performance and another profile with more lift and duration that boosts high rpm performance. Basically the best of both worlds. To my knowledge, the only different between I-VTEC and VTEC is VCT, variable cam timing (I think that's right or VTC?). Basically it's a computer controlled adjustable cam gear on the intake cam shaft. Like a set of cam gears you would buy for a VTEC engine that allow for small changes in cam timing, both do the same thing except VCT isn't static, it can change the settings as the engine is running for better emissions and high rpm performance. I-VTEC engines also spin the opposite direction.

 

Andy is correct. The traditional VTEC basically uses an oil pressure-actuated pin to lock rockers together and follow a single cam lobe. The net effect is basically a 'switching' of cams at a specific RPM. You get a good low-RPM cam at low revs, and a good high-RPM cam to keep the torque alive at higher RPMs. (Note: not *all* VTEC cars worked exactly this way. VTEC has also been used in various incarnations, both two and three stage, to improve milage by shutting valves OFF)

The strength of VTEC is that you essentially get two cams in one, with variable lift and duration. There wasn't really another system on the market that accomplished that, though some other manufacturers do now.

The weakness is that you get ONLY two (or arguably three with a 3-stage VTEC). It's either on, or it's not. There's no variability.

You can think of it like a transmission. A one speed tranny would suck for obvious reasons. Two speeds is better, but still not great. Five speeds are good. But the ultimate is an infinite number of gears (like some manufacturers, including Honda, are trying to do now with CVT).

iVTEC is the same thing, but with variable cam timing thrown into the mix. Now the engine can not only use one of two cam profiles, but it can also infinitely vary the timing via an electronically-controlled cam gear. With iVTEC, the engine can vary the lift and duration (between only two profiles), as well as the timing of the intake and exhaust cams with respect to one another (on a DOHC, doubt Honda would ever bother with variable cam timing on a SOHC, doesn't make much sense from a cost/benefit standpoint).

The Holy Grail is infinitely variable duration and lift, along with infinitely variable timing. This is all but impossible using a traditional mechanical camshaft. The valves would have to be independently, electrically controlled. You'd better believe manufacturers are looking for a way to do this, but right now it's just not practically possible.

 

Actually, supposevly BMW has a engine with magnetically controlled valves that runs without a camshaft. I haven't heard much about it, but supposevly, they're still working on longevity.

I though I-VTEC was only on the intake cam too, but maybe I'm wrong, maybe that VVTL-i (toyota's version of VTEC).

 

yea, some BMW rep came into my school once and told us about the intake that doesn't use a camshaft

 

Well if they can ever nail it down reliably, that'd be one sweet engine. Great gas mileage all around, huge low-end torque, perfectly flat torque curve that just won't die (until the bottom end explodes), and to top it all off, super-clean emissions.

Andy - I don't have a ton of experience with the iVTEC stuff, but I believe there's both. The base RSX/Si engine only has variable timing on the intake side, RSX-S has both. Not sure about a lot of other engines like the TSX (probably both) or Accord/CR-V (probably only intake).