TRUTH ABOUT BIG MUFFLERS/SILENCERS/EXHAUSTS

Royal Enfield guru Pete Snidal recently spotted something about the motorcycles.

"I notice one thing all the Bullets for sale seem to have in common - can you guess what it is?" he wrote.

Pete is the author of the acclaimed Royal Enfield Bullet owner's and workshop manual. He frequently chimes in on the Royal Enfield Yahoo message board to help troubleshoot problems owners experience.

But what could he possibly be seeing in the for-sale ads?

I guessed that maybe the Bullets listed for sale here tend to have low mileage. Obviously, some owners buy them and then sell them without riding very far. I was on the right track, but Snidal had something else in mind. He wrote:

"Look at all their exhaust systems. Something I discovered very early in life with Brit singles is that they became completely different machines with free-flowing (i.e., loud, requiring using your head about where and when to apply large gobs of throttle) exhaust systems. And that they were much less satisfactory when stock.

"An exception was the Velocettes with that monster Brooklands silencer, and the Goldstars, which already came with noisy mufflers. Some AJS/Matchless, too.

"My theory is that the owners who never 'bothered' with the first-stage mods, i.e., inlet and exhaust mods, just fell into the doldrums with their Bullets, and ended up putting them on the market. If you wonder, try putting your stock exhaust back on, and see for yourself.

"Instant Bow-Wow!"

Snidal was seeing the big, bazooka shaped factory muffler, which restricts performance, in the pictures of the bikes. Replacing it with a shorter and nosier silencer (and tuning appropriately) is an easy way to increase performance.

As Snidal observes, that makes for more owner satisfaction.

Big factory silencer affects performance.

credit : david blasco

Back Pressure in Royal Enfield

“Back pressure is the pressure drop in the flow of gases from engine to exhaust. The less power engine has to spend making pressure to push the gases from exhaust output, the more power it can send to the wheels”.


The term back pressure is misleading as the pressure remains and causes flow in the same direction, but the flow is reduced due to resistance. For example, an automotive exhaust muffler with a particularly high number of twists, bends, turns and right angles could be described as having particularly high back pressure.


The exhaust having maximum bends will have the higher back pressure resulting in negative effect on engine efficiency resulting in a decrease of power output that must be compensated by increasing fuel consumption. Less back pressure makes engine able to transfer maximum power to wheels and keeps it less heated up.


The motorcycle's exhaust pipe is connected to the cylinders in the engine. When the engine is operating, it circulates gas throughout the system. The gas expands as it circulates through the engine, then finds its way into the cylinders. Some of the gas is not expelled out of the exhaust pipe, and it then creates exhaust back pressure. All of the gas pressure should leave out of the cylinders and into the exhaust pipe at a constant rate. If the rate is thrown off balance, then you have the result of exhaust back pressure in your motorcycle. Many believe that there is no effect on your engine when motorcycle exhaust back pressure is formed. Either way, it is not normal for exhaust back pressure to occur.


Back pressure caused by the exhaust system of an automotive four-stroke engine has a negative effect on engine efficiency resulting in a decrease of power output that must be compensated by increasing fuel consumption.  

Free Flow silencers has less back pressure than that of stock silencers that is why we bulleteers prefer louder sound but the fact behind it that a free flow silencer helps in less heating up of engine and louder sound as we alwayz want.



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ROYAL ENFIELD THUNDERBIRD TWINSPARK 350cc REVIEW / ROAD TEST & SPECIFICATIONS

Royal Enfield launched its new bike the Thunderbird Twinspark in 2008. But it was under some serious scrutiny by Bajaj Auto Ltd because of the name and the twin spark technology. Bajaj patents the twin spark technology and it had previously filed a suit against TVS motors for the same reason. But according to Royal Enfield they have not breached the patent copyrights as it holds good for 75 and 250 cc engine bikes whereas the Thunderbird is of a 350 cc version and they plan to incorporate the same technology in their future series of bikes too.

Design & Engineering :

A first look, and you would be hardly able to tell the difference between the Twinspark and any other Thunderbird, till you see the engine. It’s a contemporary looking powerplant with an incorporated crankcase and gearbox projected to lessen oil seepage. Every other bit is similar; the round headlamp, double instrument pods, front disc brake, seat and pillion backrest are all the same as the normal Thunderbird’s. A notable visual difference is the shorter muffler that we received on our test bike.
 

The panels underneath the seat feature a minuscule ‘Twinspark’ sticker, which is the lone sign of this key technical step forward of the bike. Also on either side, just beneath the tank, are round reflectors; a helpful touch when you’re emerging from a side road onto a highway.

The fuel tank is sheet-metal, and the overhang welded below it is a blemish, while the fuel tank cap looks dated. The Twinspark does well to offer slow- cam chain adjusters, as compared to the more predictable system provided on most Indian models.

Drivetrain & Performance :

The all-new engine has twin-spark plugs, an automatic decompression facility and unit-construction that the company claims has answered the crisis of oil discharge, a key problem with the old engine. Although a lot does stay alike, other important changes contain a high-flow trichoidal oil pump, hydraulic tappets, an automatic primary chain tensioner and the drive chain assembly shifted to the right side in order to reduce transmission loss.

The Twinspark benefits from TCI ignition for a fine spark. You get 2bhp more, for a figure of 19.8bhp, and 2.85kgm of torque, which is a insignificant 0.1kgm more than the older version.

Start it and you instantly notice a smoother feel near idle. The handlebars don’t judder in your hands just yet. Select first gear and as you let the clutch out, it feels a bit improved. A six-plate clutch instead of four makes the difference. As you hasten through the gears, this smoothness unfortunately diminishes however, to be replaced with Royal Enfield characteristic vibrations, Which is where it goes from bad to worse, and it’s apparent that thrashing the engine is not the way to ride this bike.

Economy :

Fuel economy is not a subject of relevance among Royal Enfield bike lovers, who will buy the Thunderbird Twinspark more for its lifestyle value, than economy.

For the record, the Twinspark returns 35.7kpl in the city and 36.8kpl on the highway.

BTW according to company the fuel efficiency ranges anywhere between 45-50 kmpl.

Ride & Handling :

  

The riding arrangement of the Twinspark is classic cruiser fare, and its saddle is a sensibly pleasant place to be on long rides.

The new bike has an integrated gearbox that produces only 10% more power and torque compared to the previous Bullets. So, there is not much to rejoice. It generates a maximum power of 20 bhp and the maximum torque is 28Nm. For an instant halt the bike requires 150/280mm brakes.

The shifting of the rear brake has become easier. The suspension is not satisfactory; it is slightly stiffer but gets better with a pillion rider. Stability on straight lanes remains good but riding into curves isn’t any great. The front tyre seems to skid while breaking that causes some kind of discomfort. The bike is recommended for city riding and for a rare long drive too.


The Thunderbird uses known, large, kicked-out forks and an extended single-downtube frame. Its gas-charged dampers at the rear are par for the course for motorcycles in India, but even on their softest setting tend to jump when pushing the bike to its edge. These work best when the bike is overloaded.


The Thunderbird Twinspark is somewhat a burden in city traffic, but a steady bike on the highway thanks to its 19-inch rims. The handlebars do provide ample weight for city riding, but there is no dodging this bike’s rangy wheelbase and heft in the city.

Popularity Rating of Royal Enfield Thunderbird Twinspark In India :

The new Thunderbird Twinspark will not have a mad following like we see for Pulsars or Karizmas but is liked by people who already own a bullet and those who do not have one but have a liking for the brand. You might not see 100s and 1000s of these on roads, but one on road and it is a head turner.

Price : 

The Royal Enfield Thunderbird Twinspark is available in three colours: Silver, Black and Red and is handsomely priced at Rs 103000.(price quoted from year 2009)

At Rs.1,00,000+ the bike is not cheap, but it is a legend cloaked in modern wizardry. Enfield claims the Thunderbird TwinSpark is maintenance free though only time will tell, as it is too early to comment on this. 

Verdict :

The dreary general quality, the heavy price tag and the out-of-date technology make sure you do not buy this bike by using your head. Yes, the new engine is better and more modern, but then these are changes that should have been made a long time ago.

But looking at the Thunderbird Twinspark as such is missing the point totally. It is a bike you buy with your heart.

Technical specifications :

  

Engine	Single Cylinder, 4 Stroke, OHV, Dual Spark Ignition Engine, Air Cooled
Displacement	346 CC
Bore x Stroke	70mm x 90mm
Maximum Power	19.8 bhp @ 5250 rpm
Maximum Torque	28 Nm @ 4000 rpm
Transmission	5 Speed (left foot gear shift)
Ignition	Digital TCI (Transistor Coil Ignition)
Carburetor	BS29 / UCAL
Dimensions
Ground Clearance	135 mm
Width	780 mm
Wheel Base	1370 mm
Length	2120 mm
Height	1080 mm
Tyres
Front	3.25 x 19", 6/4 PR
Rear	3.5 x 19", 6/4 PR
Electricals
Electrical System	12 Volts
Head lamp	35W/35W Halogen, MFR
Brakes
Front	Hydraulic Disc Brake (Disc dia 280mm)
Rear	Internal Expansion (Drum), 6"
Maximum Speed
Speed	120 Kmph
Suspension
Front	Tele Scopic With Hydraulic Damping. Stroke 130mm.
Rear	Swing arm With Gas Shock Absorbers stroke 80mm

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