If you’ve been following technical developements in MotoGP for a while, you’ve certainly heard about the “big bang” engines. The “big bang” concept – which is basically a change in the firing interval of the cylinders – was originally developed back in the days of 500cc two-stroke GP bikes, and has recently been applied by both Yamaha and Kawasaki on their inline-four MotoGP engines.
A standard inline-four fires its cylinders at regular intervals – one cylinder every 180 degrees of crank rotation. This creates a constant delivery of power to the rear wheel, which can make it difficult to maintain rear-tire traction, or to regain said traction once it has been lost via wheelspin. Since this effect becomes more pronounced as power output increases, it is especially noticeable in current Superbikes (many putting out 200+ horsepower) and MotoGP bikes (220-250 horsepower).
Years ago, Superbike racers discovered that it was easier to modulate the power to prevent wheelspin on the Ducati V-twins than it was to do the same on the Japanese inline-fours. This is because there is a longer interval (in terms of both time and crankshaft rotation) between cylinders firing, which gives the rear tire a “break” – time to recover traction and match its speed to that of the motorcycle.
The “big bang” engine attempts to transfer this characteristic to the inline-four by changing the firing intervals of the cylinders. By firing two cylinders close together, followed by a long break, then the other two cylinders in close succession, then another long break before the cycle begins, a “big bang” motor gives the tire some recovery time. This gives enormous benefits to rideability and tire wear.
The disadvantage is that these uneven firing intervals throw off the balance of the motor, creating excess vibration that can be damaging to the bike and annoying to the rider. The life span of the motor’s internal components is also affected, since there are now effectively two large power pulses per power cycle instead of four smaller ones. To get an idea of how this will affect the durability of the motor, just walk over to the nearest glass window and knock on it lightly four times. Now knock on it twice as hard, two times. See what I mean?
These negative affects can be counteracted, however. Stronger internals will resist the bigger power pulses, and a balance shaft can dampen the excessive vibrations – although balance shafts create parasitic losses that sap horsepower.
Recently we have seen reports that Virgin Yamaha is using a “big bang” firing order on its Yamaha R1 race bikes in the British Superbike Championship. This is the first we’ve heard of the “big bang” in a road-based bike, rather than the pure racing prototypes of MotoGP. Hearing about the Virgin R1, we started to wonder if the “big bang” design will ever make it into a production inline-four streetbike.
As the power output of modern 1000cc sportbikes climbs to ever more ridiculous heights, rideability will start to become the deciding factor for many potential buyers (hopefully it already is!). If a production inline-four 1000cc from one of the Japanese “big four” were to be redesigned to utilize the “big bang” firing order, it could dominate the category by allowing more of its excessive power to be safely used on the streets.
Our bet on which manufacturer will be first to debut a “big bang” streetbike lies with Yamaha. They have a tradition of thinking outside the box (a 400cc four-stroke motocross bike!), and they have already been using the “big bang” design since last season in MotoGP. Seeing a private race team like Virgin Yamaha using it in an R1 might be just the inspiration Yamaha’s engineers need!
