All over this board I keep reading about people who love "hitting VTEC". People who have just broken their car in can't wait to "hit VTEC" above 6,000rpm.
I'm confused.

Someone please correct me on this one.

VTEC is always on. When you are accelerating, stopping, reving, always. It's valve alteration that allows for optimum timing accross the entire RPM range to get the most out of the engine. The S2000 is not a turbo that jolts you forward suddenly. Yes, at 6,000rpm the engine roars, the car accelerates swiftly (almost frighteningly so), but it's not as if VTEC turns on as if it was off before. If you feel greater acceleration at the top end it has more to do with the meager 157ft-lbs of torque our cars have.

Can someone educate me on this? This is how it was explained to me by the Honda Rep at the car show and from an engineering standpoint, this makes more sense then VTEC suddenly turning on at the high rpm range.

I invite SOMEONE WHO KNOWS FOR SURE to shoot me down if this is crap, but I'd like to understand how VTEC REALLY works.

 

[QUOTE]Originally posted by Ajjra
[B]All over this board I keep reading about people who love "hitting VTEC".

 

When people refer to vtec "kicking in" they are referring to the crossover from the mild cam lobes to the more aggressive cam lobes at around 6000 rpm. Cam lobe crossover is unique to vtec engines so people associate the crossover as vtec'ng. I do believe that variable timing occurs across the entire powerband so I guess vtec is technically always on.

John

 

So if I understand this correctly, what people really feel is the DOHC switching over. VTEC is in effect always, varying your valve times in an optimized way?

 

VTEC isn't always on. It is simply a two-stage system. It does vary the timing, but not infinitely. The only Honda motors that are capable of that are the new i-VTEC motors, which in addition to the two-stage cam, alter the cam-phase infinitely. So VTEC actually does kick on at around 6000rpm, and when it does, the valve timing changes along with the valve lift.

 

Therefore all VTECs are DOHC?

 

Honda makes SOHC VTEC engines as well, but the system is completely different. Up to a certain rpm, one intake valve opens fully and the other opens just a hair (to induce swirl in the combustion chamber). Above a certain rpm, both intake valves open all the way. The exhaust valves are unaffected...they do the same thing at both high and low rpms.

On DOHC VTEC engines, the dual cam lobes operate on both the intake and exhaust valves. Hope this clears things up .

 

[QUOTE]Originally posted by Ajjra
[B]So if I understand this correctly, what people really feel is the DOHC switching over.

 

SOHC has 5 lobes per cylinder, all packed onto one camshaft. 2 for normal intake, 2 for normal exhaust, and 1 for high RPM intake.

DOHC has 6 lobes per cylinder, 3 on each camshaft. 2 for normal intake, 2 for normal exhaust, 1 for high RPM intake, and 1 for high RPM exhast.

The reason SOHC doesn't VTEC the exhaust is that they must choose intake or exhaust. And since an engine evacuates a cylinder more efficiently than it fills, the intake side is where the most help is needed.

DOHC's are more precise because the camshaft is very close to the valves, and very small rocker arms (cam followers if you prefer) are necessary. Smaller parts mean a higher redline. And since a higher redline requires better breathing, the exhaust VTEC actually helps nicely.

The SOHC engine has the normal and high RPM performance profiles rather close to each other because of the limited redline. In the DOHC engine, the profiles are further apart, and the switchover is more noticeable (less linear).

 

YOUR ALL WRONG!
















j/k


Anyways here's a good read

VTEC IMPLEMENTATION
iVTEC Explained


Peace