I read an article by Rick Sieman in 1984 about the fastest stock production dirt bike ever produced. I had to have one. Then another and another. Here is a question asked of Super Hunky:
Q: What's the fastest dirt bike ever made?
A: The fastest real dirt bike ever was the KTM 495. When I was editor of Dirt Bike, we geared one to the moon and had Rod Bush do 123.75 miles per hour on El Mirage Dry Lake with that particular bike. I believe the year was 1981. I have not heard of any other true stock dirt bike go faster under verifiable conditions.
Rod Bush at 123.75 mph! 1981
The bike in this post is my third Great White. It's a 1983 5-speeder and a brute of a bike. It's nearest competitor is the '83 Maico 490 Sand Spider. I had considered
the Maico but couldn't get over the 495's I owned in the 80's. I purchased this
one from Barry Higgins shop in Douglasville Georgia in 2001. It's still in excellent
condition ready to race. It is a machine with
so much power that when your doing 80-90 mph across the desert, it's still
trying to rip the arm's out of your shoulders! The bike demands great respect at all times. It is especially suited
for open-desert racing where it can gobble up those wide open spaces like dessert. Motocross? Not so good as it's a tough one to negotiate the corners
quickly... but tons of power and I like that.
The bike was given a going through and needed minimal adjustments but the suspension and gearing was set up for MX as I longed to hit the track again (no pun intended but I did eventually hit it hard).
The Great White arrives with forklift holes in the crate! All is good though.
Massive 40mm Bing magnesium carb, and that huge cylinder!
Eight 10 mm head studs and a massive exhaust port offer clues to loads of power!
~ Engine Mystery Expained ~
The KTM 495 engine is
over-quadratic. That means that the bore is bigger than the stroke making the
engine extreme from this perspective. It has a bore of ΓΈ92mm and a stroke of
only 74mm. Most modern two stroke MX engines has almost equal bore and stroke. One
has found that to be ideal. Thus, the 495 motor revs like a 250 but with twice
the torque and power! The short stroke means two things. First that the piston
is moving relatively slow in meters per second since it travels shorter
distance than if the stroke was longer. We'll take that again, the piston is
moving slower and travels less distance at a given RPM (Revolution Per Minute)
than most engines having the same displacement. The consequence is less moving
energy. Kind of less flywheel effect. The other thing is that due to the large
bore the channels in the cylinder can be larger (wider) and the piston also has
a larger surface to rest on, wall area. Now the larger bore creates a higher
piston pressure when the expanding gases burns out. Compare it to a hydraulic
piston. A large piston moves a short distance with great force whereas a small
piston travels a long distance but doesn't have the force. The 495 piston moves
a short distance but is pressed down with much greater force. What will happen
is that you will get a lively engine that can increase it's revolution per
minute during a very short period of time. On the other hand it wouldn't do
very well as engine in a truck since it easily could be overloaded once you
apply heavy work on it. The 495 engine doesn't develop extremely high HP
ratings but it could climb from a low RMP to high RPM in a extremely short
period of time. This means that is should and could out-accelerate almost
anything dirt bike alike unless the straightway is very long and uphill. Then
the RPM climb is to no use and sheer power is more important. The larger
cylinder wall area is mostly a good thing though meaning a possibility to have
wider channels allowing more fresh gases to come in and out. It is also better
from a wear point of view. On the other hand the higher piston pressure
stresses the wrist pin and the crank a bit more. The conclusion is that the
larger bore, smaller stroke engine results in: more difficult to start, higher
risk of kickback, bad idle properties and difficult to ride smooth when very
slippery for example. On the other hand you get high power output, great
acceleration and a lively engine. The mass of the huge piston makes up most
downsides when it comes to idle and so on. Absolutely an astounding engine... Bengt Hahn
Marzocchi 43mm forks and White Power Twin Clicker shock deliver nice suspension
Stock front disc is converted to old s'cool drum set up for VMX.
All set up field testing the chassis and roost factor - Success.
As she sits in 2015
I love my CZ's but the 495 beast is still my all time favorite roost meister and all around fun bike to ride. The power and comfort at speed is just too addicting to shake off. My advice to anyone wanting to experience the Great White is - get yourself in great physical shape before you mount her and be smart and alert at all times or she will break you before you know what happens. This comes from experience of being a victim in the hospital for 3 weeks! Thanks for stopping by... EJ
