want a cookie?

 

It could be completely centrifugal in nature, no electronic control. That would mean it might be adaptable to earlier model EVO’s!

 

isn't it oil pressure camshaft shift type of activation? so wouldn't you really need the head plus hte camshaft that has the double ground profiles.

and actually superhatch... could you elaborate on how the electronic portion works... and how they can mess around with the timing on the fly... cuz in my celica gts the second profile would snap in and i'm sure it's like that in the vtech motors too... so what exactly are you referring to? cuz i'm really not in the know about this stuff.

 

MIVEC system on the intake cam gear! Sweet!

 

MIVEC doesn't have two different cam lobes like VTEC... it just shifts the intake cam timeing.

Keith

 

If memory serves me, I believe it has the intake cam retarded for more low end tq at low rpm's and then when rpm's rise it makes the cam advance to help with top end (increasing the duration the valve is open, (but i guess it could be the other way around)

 

but how does it do this advancing... you gotta have some lobes doing something right? (i'm honestly just asking... not tryinna give attitude... already admitted i don't know how it works.)

 

no...there are no lobs, it acts like an ajustable cam gear. It allows the cam gear to advance or retard the actual cam. Its very different from honda's Vtec that has a seperate lob the switchs over upon oil pressure.

 

You gotta watch your terminology there, it doesn't increase duration, the duration the valve is open is purely a function of the cam profile, which is fixed. What does vary is the amount of overlap (the time both the intake and exhaust valves are open at the same time...

 

No, the lobes don't have to change to advance the cam timing... The cam gear is traditionally bolted directly to the camshaft, so every degree that the cam gear spins the cam spins equally. Well, this setup put a servo between the cam gear and the cam, allowing the cam to open the valves at different times depending on where the servo has the cam timed. However, the cam profile itself is fixed, the valve will still open the same amount of time at the same lift, what changes is WHEN the valve opens, relative to the piston position.

 

Ok, there are two things happening on a i-VTEC and a VVTL-i motor.

The camshafts physically have two lobe profiles that are spinning around inside the head. There are also extra rocker arms following these extra cam profiles. At a certain RPM the ECU sends an electronic signal to a solenoid on the head that opens an oil passage. When this passage opens, oil pressure flows into the rocker arms that are following the low-lft low-duration cam profile and forces pins out of the side that cause those rockers to lock into the rockers following the high-lift long-duration lobes. Essentially from that point forward, the valves open according to the new profile, until that solenoid is closed, and the springs release the pins and the rockers start following the low profile again. There is no smooth transition going on, it is an on/off switch, you follow one or the other. If you've ever head one of these motors with an intake on it, you can audibly hear the change, and I personally think it sounds pretty cool

The other system at play is like what is on this Evo 9 motor. The ECU can change the phase of the intake cam, in the exact same manner of an adjustable cam gear. The benefit of having it adjustable on the fly, is that you can improve low end response, torque, fuel economy, and emission, but then when you put your foot in it the ECU can shift the phase of the cam for more power. It is electronically controlled because there is a stepper motor inside that unit that shifts the cam gears position relatice to the cam.

Old-school VTEC motors only had the dual lobe setup....

VVT-i and MIVEC as well as a host of other engines out there have only the second part.

i-VTEC and VVTL-i motors have both....

I hope this clears things up, cause I don't want to type anymore...