How Throttle Blipping Came To Be

[Hugh Janus]

Kevin Cameron (Robert Martin/)

“Vtt-nn! Bark! Rumble!” Who can resist? Here we all are, waiting for the stoplight to turn green, and we are anticipating departure by blipping our throttles. Why do we do it? Cruiser guys do it. Tenured professors of English literature do it.

Because motorcycle engines and their fuel systems have been so civilized for decades, there is no longer any physical reason to blip the throttle. We are not “clearin’ ’er out,” because there’s nothing to clear. All bikes now have near-perfect air-fuel mixture at all times because that’s the job of their digital engine management systems.

That became obvious when Cycle World testers used to run for top speeds at their “secret desert road.” Here comes the bike, sounding strong and sharp; 192 mph! Hot stuff. Moments later the test rider rolls back to the group, the bike’s engine burbling happily and stably at idle.

Or think of dragstrip riders. As the tree starts down, they smoothly bring the revs up to their chosen launch rpm, hold an instant, and go. No brum-brum, no vtt-nn, vtt-nn. Bring revs to the launch point and go.

Yet remember the generations of racing mechanics, warming up bikes with rhythmic bursts of throttle, tach needles swinging back and forth. Hailwood’s Honda 250 six warmed up with a rapid, irregular WOOP-woop-WOOP. Manx Norton 500 singles prepared for action with BRUM-bah, BRUM-bah. It was exciting. It was anticipatory. It was a sonic celebration.

But why did they do it? Why not just start the engine, check for oil circulation, and leave the bike to warm up on the stand?

There was a real reason for throttle blipping, and in some cases it still exists today in certain racing engines. In a valve train with high-pressure valve springs, it is the nature of the lubrication between cam lobes and tappets that sets the speed of minimum idle. Above some critical speed, the cam lobes are spinning fast enough to generate a full lubricating oil film between themselves and their tappets (this can be measured by such means as electrical resistance between the parts). But below that speed, the slower motion allows more time for lubricant to be squeezed out, leaving only a partial oil film. Anti-wear additives in the oil can help here, protecting bare surfaces from scoring. But in some race engines, idling just destroys the cams. Because oil films need speed to form completely, friction rises at low rpm. Both Professor Heywood at MIT and Paul Jette at Del West (the California makers of titanium valves and pneumatic spring systems) told me that rising friction at low speed puts a lower limit on idle rpm. Jette noted that many racing valve systems will fail promptly if idled.

On page 3 of general information regarding the Cosworth Norton JAB engine, dated 5/18/1976, it says, “The engine must not be allowed to idle under 2,000 rpm or excessive cam and tappet wear may be experienced.”

That is why racing mechanics for 100 years have warmed up engines by throttle blipping. And that made it cool.

Production machines naturally have to be engineered to idle indefinitely without valve train damage (ever shuffle forward for a solid 10 minutes in a long summertime toll queue?). The bikes we buy and ride are given cam lobes and tappets wide enough and valve springs soft enough to guarantee satisfactory lubrication at idle. They have oil pumps that at idle bathe moving parts through a multiplicity of holes through cam lobes, supplied through oil galleries into their hollow interiors. This is just sensible engineering.

As superior oil additives and super-hard and smooth anti-friction coatings such as DLC have come into general use, even some of today’s 18,000-rpm MotoGP engines are allowed to idle during warm-up.

All that is irrelevant for street riders, who continue to enjoy the sound and fury of a bit of throttle-blipping at stoplights. Its origin forgotten, throttle-blipping has become part of the fun.

Source

[Specs]

When I had my Yamaha RD250 in the early seventies, I had to blip all the time because the bloody thing would keep oiling up one plug or the other, and it was the only way to stop it from stalling. The second cylinder would usually fire up half way around a corner in the wet, causing a huge pucker factor. Always kept me alert!

[XTreme]

15 minutes ago, Specs said:

When I had my Yamaha RD250 in the early seventies, I had to blip all the time because the bloody thing would keep oiling up one plug or the other, and it was the only way to stop it from stalling. The second cylinder would usually fire up half way around a corner in the wet, causing a huge pucker factor. Always kept me alert!

I used to have to run a different temperature plug in the middle cylinder on my H1.

Difficult to believe that we just accepted these things as normal.

[Catteeclan]

Middle cylinders were alway trouble on all those triples. Nice when right but not normally for long.
Not had a prob with any of my bikes for tickover, blipped because I could.