HONDA 2002 VFR800A
The Technical Blurb

All the bits that make the V-Tec system work (try clicking for a bigger image).

V-TEC (No-one seems to know what this stands for)

To get an internal combustion engine to work as efficiently as possible (and thus produce more power), you want to make sure that you get as much fuel/air mixture into the cylinder as possible. In reality, a 800cc motor will unlikely ever see a full 800cc of said mixture, thanks to air flow restrictions and and limited time to fill the space (it takes a while to get the mix moving every time the inlet valve opens).

Anyway, to get to the point, one of the factors in making the incoming mix actually come in is the size of the inlet hole. You'd think that the bigger the hole, the more you get it. True, but this is only true at higher revs. At lower rpms too large a hole can actually cause the mix to come in too slowly, whereas a smaller hole has a speeding up effect, and ironically fills the cylinder more efficiently. It also adds some turbulence that helps the burn effect, but that's a whole other story.

You have to click for the large image, but this is how it all works below 7000rpm.	And this is what happens above 7000rpm.

The same theory of gas speed and small holes applies to exhaust valves, but not to empty the combustion chamber (the rising piston makes sure of that). No, the high speed of the exiting exhaust gases means that by allowing a bit of valve overlap (inlet valve opens before the exhaust valve is fully closed), the exhaust gases leaves a bit of a vacuum behind it which then acts to help pull the new mix into the cylinder - ultimately helping that fill-the-cylinder-to-the max thing.

In effect, a two valve head is better than a four, up to a certain rev point, at which time there just isn't enough time to get the air in through that little hole, so more holes is better at this point. What the V-TEC system does is make a four valve head into a two valver at lower rpms (below 7000), then kicks in the extra two valves when you need them most, allowing enough gas in despite the shorter time duration in which to do this.

And here are the results of all this trickery.

How does it do this? Good question. The V-TEC valves have a separate collar under the bucket (which the cam acts upon) and located around the top of the valve. Below 7000rpm, as the cam nose pushes against the bucket, it just moves the collar over the valve. Thus the valve remains closed.

At 7000rpm, a sensor triggers a spool valve to squirt some oil to the V-TEC valves in the cylinder head. Here, the oil pressure pushes a pin to slide through the collar and into a notch in the valve. When the cam next comes around, the cam nose now acts on the collar and the valve, which in turn pushes the valve open. Once you drop below 7,000rpm, the oil pressure drops off and a small spring pushes the pin back away, thus reverting back to two valves per cylinder.

Simple init ... no, not really.

ABS (Anti-lock Braking System)

You don't want that wheel to lock up!

The basic idea of ABS is to have a sensor monitoring the spinning wheel so that when it stops spinning (i.e. the wheel has locked up) it tells the brakes to let go.

Once the wheel starts to spin again, the sensor allows brake pressure to resume again, reapplying braking force. Inevitably it locks up once more, the pressure is released again and the wheel starts to rotate, and so it continues until you stop in a safe manner. The idea is you have maximum braking until lockup (at which point you're either skidding and not braking efficiently at all, or sliding on yer arse), at such time it releases the brake and reapplies it as many times as is necessary.

Where Honda have made a fine tune in this idea is to factor in overall speed of the bike along with wheel rotation, and feed this into the main computer many times a second. However, instead of waiting for lockup before releasing, a smidge before that point is reached it bleeds off just enough pressure to usually prevent it getting into lock up mode (although momentary lockups are possible). The result is a seamless ABS operation, instead of the grab/release/grab effect of other ABS systems, or so the theory goes.

LBS (Linked Braking System)

This is a lot easier than trying to describe the linkage system. PCV stands for Pressure Control Valve.

Guaranteed to stir up controversy in many riders who don't like the idea of having any braking control taken away from them. Linked braking systems are exactly what the name suggests - some kind of linking between the front brake and rear, via the hydraulic system.

The theory is that it makes either brake lever more effective than if they were used on their own. Grab a handful of front brake on an LBS and a little bit of the back is applied too (which also helps to prevent front end dive). Stomp on the rear and there's just a tad of front to help things come to a smooth stop.

In the case of the new VFR, the front lever actuates all three pistons of the caliper on one side, but only two on the other. It also actuates the middle piston (of three) at the rear. Use the rear brake lever and you're activating the other two pistons on the rear and the, so far unused, one at the front.

However, in order to avoid the front one coming on too strong when you're just lightly using the rear (i.e. during low speed manoeuvring - like an illegal U-turn), they've also included a sensor and proportioning valve to reduce front brake pressure accordingly. Thus giving the required fine control to the rider.

Very good then. Any questions?