Two camshafts in one — a mild cam for the school run and a wild one that arrives at 5,500 rpm.
1989·1.6 L inline-four·160 PS at 7,600 rpm·8,000+ rpm·~5,500 rpm
1· THE STORY
The engine that refused to choose
Every camshaft is a compromise: a gentle profile idles sweetly but suffocates the engine at high revs; a racing profile breathes at 8,000 rpm and barely idles at all. In 1989 Honda’s B16A refused to choose — each valve got two cam lobes, and a small oil-pressure pin locks the rockers to the wild lobe at high rpm, swapping profiles mid-stride. A 1.6-litre hatchback engine that revved past 8,000 and gave a hundred horsepower a litre, with no turbo and no tantrums.
1.6 L inline-fourDisplacement160 PS at 7,600 rpmPower
2· WHY IT MATTERED
The breathing compromise
How long the valves stay open — the cam’s duration — sets an engine’s character. Short duration fills the cylinder well at low revs; long duration keeps feeding it when the pistons are sprinting. One profile cannot do both: whatever the cam grinder chooses, half the rev range pays for it.
3· WHY IT MATTERED
A pin swaps the profiles
VTEC’s answer is mechanical sleight of hand: beside each pair of gentle lobes sits one aggressive lobe working a free-floating rocker. At the switch point, oil pressure slides a pin through all three rockers, locking them to the wild lobe — full race-cam lift and duration, engaged in milliseconds. Back off, the pin retracts, and the engine goes back to sipping.
4· WHY IT MATTERED
A hundred horsepower a litre, for the masses
The B16A gave screaming top-end power AND a docile idle AND commuter reliability — a combination tuning folklore said was impossible. The crossover surge became a culture of its own, and the idea conquered everything: variable valve timing, in some form, is now in virtually every petrol engine made.
Two torque curves in one engine: rev past the switch point and watch the wild cam take over — then drag the switch point around and see why Honda put it where they did.
Readout
Mild cam workingshort duration, sweet idle, strong midrange — and a ceiling coming
Torque (vs best)71%
Power (vs peak)49%
Cam in chargemild
Honda’s switch point~5,500 rpm
The yellow envelope is what the driver gets: the best of both cams, stitched at the switch point. Notice the step where the curves cross — that little surge as the pin engages is the crossover generations of drivers chased.
Deep dive · Why engines have a redline· opened from Honda VTEC (B16A)
Timelines · Engines · go deeper · Honda VTEC (B16A)
Why engines have a redline
One number on the dial — really three different walls arriving almost together.
valve float·inertia — squared·breathing·margin below the first wall
1· THE IDEA
The rev limit: springs losing a race, inertia squaring, cylinders running out of breath
A redline looks like a single fact — past here, damage — but no one thing fails there. It is where the manufacturer draws a safety margin below the FIRST of several independent limits, each with its own physics and its own cure. That is why the number varies so wildly between machines burning the same fuel: a family diesel gives up at 4,500 rpm, a superbike screams past 14,000, and a Formula 1 engine has run beyond 19,000.
2· WHY IT MATTERS
Valve float — the spring loses a race
A cam can PUSH a valve open at any speed, but only its spring can bring it back — and the valve’s inertia grows with the square of engine speed while the spring’s strength stays fixed. Past some rpm the valve stops following the cam and floats, hanging open when it should be shut. In an interference engine the piston, arriving on schedule, may meet it. Racing’s cures: F1’s pneumatic springs of compressed nitrogen, and Ducati deleting the spring entirely with a closing cam lobe.
3· WHY IT MATTERS
The inertia hammer
A piston stops dead and reverses twice every revolution, and the force to do that grows with the SQUARE of speed: double the revs, four times the load on rods, bolts and bearings. At road-car redlines each piston is already stopped and restarted with roughly the weight of a small car, a hundred times a second. Nothing snaps at the line itself — but the square law erodes the safety margin above it brutally fast.
4· WHY IT MATTERS
Running out of breath
Each intake stroke gets a fixed slice of crank angle, so at high rpm that slice lasts milliseconds — and the air, which has inertia, simply stops arriving in time. Cylinder filling falls, torque falls with it, and power stops rising even before anything breaks. This is the gentle wall: the engine does not explode past its power peak, it just stops being worth revving.
5· TRY IT
Race the spring
Rev the engine and watch the valve’s inertia climb its square law towards the spring’s fixed strength — where the curves cross, the valve stops obeying the cam. That crossing IS the mechanical redline.
Readout
Valve controlobeying the cam
Inertia vs spring39%
Float begins7,200 rpm
One representative road engine. Stiffer springs move the line up — and steal power all through the range to compress them. Pneumatic springs stiffen exactly when squeezed harder, which is how F1 bought its 15,000+ rpm.