Technical Insights
by Elden Carl
by Elden Carl
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Copyright © 2006 Top Gun Motorcycles. All rights reserved. Distribution or publication of this document (electronic or otherwise)
is prohibited without the express written consent of the author. For more information or to request permission to publish this
document, please see our contact page. For information on our pledge to maintain your privacy click here. To learn more about
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is prohibited without the express written consent of the author. For more information or to request permission to publish this
document, please see our contact page. For information on our pledge to maintain your privacy click here. To learn more about
your friends at Top Gun Motorcycles, read about us here.
What's NEW!
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| Cylinder |
| Head |
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You can see the results obtained in the
series of graphs (a table of actual
temperature readings is included at the
bottom of the page). The DR-650 ran hotter
at every point, particularly at the cylinder and
head. Also, note that both bikes maintained
fairly stable temperatures throughout, a
positive attribute for both cooling systems.
Also note that the downhill comparison
showed a measurable reduction in cylinder,
and especially head, temperatures on the DR.
OK, Deuce, but what does that tell me?” First
of all, don’t be surprised at the higher head
and cylinder temperatures of the DR. The
KLR-650 has a water jacket to absorb and
dissipate heat through the cooling system.
The DR cylinder is lined with nicosil which
speeds the transfer of heat from the
combustion chamber to the outside. Air
convection and an efficient oil cooler also
contribute to cooling. I would be more
concerned if the DR wasn't hotter at the
cylinder and head, because more of that heat
would be sinking into the rings and piston.
Also, I would say that the oil cooler works
quite well as evidenced by the stable
temperatures around the engine case and oil
sump. The decrease in temps for the DR on
the downhill leg also lends credibility to its
ability to shed heat. It took advantage of the
lower strain on the engine and managed to
cool off measurably.
We took one reading at the header adjacent
to the exhaust outlet which led to a couple of
interesting observations. The temperatures
were 280 degrees for the DR and 250
degrees for the KLR; the KLR is actually
creating a lot of heat internally even though
the cylinder and head temperatures don’t
show it. Also, the small difference between
the exhaust temp and cylinder/head temps on
the DR highlights its efficiency at transferring
heat outward.
Although only three stops, the temperatures
were pretty stable on each bike and I don’t
think more stops would necessarily have
revealed additional information. Remember,
the intent was to get an idea of where the
bikes were running in relation to temperature,
and note the differences between them as
well as any trends.
Lessons Learned. First, the DR runs hotter.
In our experience though, we’ve never heard
of a DR overheating, and we’ve found they
use much less oil than the KLR. I recently had
the opportunity to attend a Motorcycle Safety
Foundation Experienced Riders Course.
Those of you who’ve taken one know that you
spend a good part of the day either idling, or
in first or second gear at no more than 20
mph. This day was well over 80 degrees,
sunny, and in the open on a hot asphalt
course. A rider on a Harley Davidson Road
King commented that his bike was cutting out
due to the heat. The DR never missed a
beat, thanks to its hard working oil cooling
system which includes an oil jet that
constantly sprays the underside of the piston
dome with oil as well as an oil feed coming
straight from the oil cooler to cool the top
end. For DR riders, the hotter temperatures
should at least make you take pause before
deciding to use a cheap motor oil (we
recommend Mobil 1 Synthetic, Golden
Spectro, HP4M, or similar high quality oil), or
making any engine modifications that might
increase temperatures even more.
For KLR riders, you can see how much work
your water jacket does. Make sure you check,
and properly service as necessary, your
coolant. Since the KLR is not designed to
pass heat in the same manner as the DR,
you don’t want to handicap your cooling
capacity.
Finally, in stock configuration the DR is
geared higher than the KLR, especially 5th
gear which seems more like an overdrive.
Remember that the deciding factor on how
you gear your bike should be how you ride
your bike. If you load it up with gear, ride tight
twisty roads, or even have a tall sitting height
like me (lots of wind drag!), you probably
want to add a tooth or two to the rear
sprocket. However, a smaller, lighter rider
who doesn’t put a lot of extra weight on
series of graphs (a table of actual
temperature readings is included at the
bottom of the page). The DR-650 ran hotter
at every point, particularly at the cylinder and
head. Also, note that both bikes maintained
fairly stable temperatures throughout, a
positive attribute for both cooling systems.
Also note that the downhill comparison
showed a measurable reduction in cylinder,
and especially head, temperatures on the DR.
OK, Deuce, but what does that tell me?” First
of all, don’t be surprised at the higher head
and cylinder temperatures of the DR. The
KLR-650 has a water jacket to absorb and
dissipate heat through the cooling system.
The DR cylinder is lined with nicosil which
speeds the transfer of heat from the
combustion chamber to the outside. Air
convection and an efficient oil cooler also
contribute to cooling. I would be more
concerned if the DR wasn't hotter at the
cylinder and head, because more of that heat
would be sinking into the rings and piston.
Also, I would say that the oil cooler works
quite well as evidenced by the stable
temperatures around the engine case and oil
sump. The decrease in temps for the DR on
the downhill leg also lends credibility to its
ability to shed heat. It took advantage of the
lower strain on the engine and managed to
cool off measurably.
We took one reading at the header adjacent
to the exhaust outlet which led to a couple of
interesting observations. The temperatures
were 280 degrees for the DR and 250
degrees for the KLR; the KLR is actually
creating a lot of heat internally even though
the cylinder and head temperatures don’t
show it. Also, the small difference between
the exhaust temp and cylinder/head temps on
the DR highlights its efficiency at transferring
heat outward.
Although only three stops, the temperatures
were pretty stable on each bike and I don’t
think more stops would necessarily have
revealed additional information. Remember,
the intent was to get an idea of where the
bikes were running in relation to temperature,
and note the differences between them as
well as any trends.
Lessons Learned. First, the DR runs hotter.
In our experience though, we’ve never heard
of a DR overheating, and we’ve found they
use much less oil than the KLR. I recently had
the opportunity to attend a Motorcycle Safety
Foundation Experienced Riders Course.
Those of you who’ve taken one know that you
spend a good part of the day either idling, or
in first or second gear at no more than 20
mph. This day was well over 80 degrees,
sunny, and in the open on a hot asphalt
course. A rider on a Harley Davidson Road
King commented that his bike was cutting out
due to the heat. The DR never missed a
beat, thanks to its hard working oil cooling
system which includes an oil jet that
constantly sprays the underside of the piston
dome with oil as well as an oil feed coming
straight from the oil cooler to cool the top
end. For DR riders, the hotter temperatures
should at least make you take pause before
deciding to use a cheap motor oil (we
recommend Mobil 1 Synthetic, Golden
Spectro, HP4M, or similar high quality oil), or
making any engine modifications that might
increase temperatures even more.
For KLR riders, you can see how much work
your water jacket does. Make sure you check,
and properly service as necessary, your
coolant. Since the KLR is not designed to
pass heat in the same manner as the DR,
you don’t want to handicap your cooling
capacity.
Finally, in stock configuration the DR is
geared higher than the KLR, especially 5th
gear which seems more like an overdrive.
Remember that the deciding factor on how
you gear your bike should be how you ride
your bike. If you load it up with gear, ride tight
twisty roads, or even have a tall sitting height
like me (lots of wind drag!), you probably
want to add a tooth or two to the rear
sprocket. However, a smaller, lighter rider
who doesn’t put a lot of extra weight on
| Oil Filter Cover |
| Clutch Cover |
| Dyno Cover |
the bike and rides open roads can probably pull 5th gear with stock gearing. The KLR-650
engine seems to handle lugging better than the DR-650. The heavier KLR flywheel helps
keep the crank moving and the one-spark combustion chamber acts like a "C average"
high school student – it’ll do the minimum, but it’s more than happy to shove some of the
work right out the exhaust ports. The DR gets less help from its lighter flywheel and
combined with its over-achieving two-spark combustion chamber, gives the impression
from the saddle that the engine is really hammering away at itself. The key is to listen to
your engine. Don’t make it work too hard. If riding conditions are working against you and
you can’t keep your revs up, drop back to 4th and give it a break. For you DR riders out
there, I get the following RPM/MPH readings with 14/42: 4000/60, 4500/68, 5000/76.
engine seems to handle lugging better than the DR-650. The heavier KLR flywheel helps
keep the crank moving and the one-spark combustion chamber acts like a "C average"
high school student – it’ll do the minimum, but it’s more than happy to shove some of the
work right out the exhaust ports. The DR gets less help from its lighter flywheel and
combined with its over-achieving two-spark combustion chamber, gives the impression
from the saddle that the engine is really hammering away at itself. The key is to listen to
your engine. Don’t make it work too hard. If riding conditions are working against you and
you can’t keep your revs up, drop back to 4th and give it a break. For you DR riders out
there, I get the following RPM/MPH readings with 14/42: 4000/60, 4500/68, 5000/76.
We’ll run more comparisons in the future and we’ll keep you posted. If there’s something
you’ve always wanted to know, drop us a line. In the meantime, check your six and ride
safely!
you’ve always wanted to know, drop us a line. In the meantime, check your six and ride
safely!
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* All temperatures are degrees Fahrenheit
| Top Gun Motorcycles |
