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Scythe Grand Kama Cross CPU Cooler

The Scythe Grand Kama Cross is a down-blowing CPU cooler featuring a large 140mm SlipStream fan, 4 copper heatpipes twisted to form a “X” formation, and an relatively small stack of aluminum fins. Does it have what it takes to compete with the big tower heatsinks?

May 24, 2010 by Lawrence Lee

Product
Scythe Grand Kama Cross
SCKC-2000
CPU Cooler
Manufacturer
Scythe
Co., Ltd.
Street Price
US$40~$50

As computer microprocessors continue to ramp up in speed and power consumption,
modern motherboard components that deal with power management are subject to
an ever increasing amount of stress. Current high-end motherboards ship with
high quality components and heatsinks for the voltage regulators as manufacturers
expect enthusiasts to dish out even more stress through overclocking. It is
ironic that these same users typically use large side-blowing tower CPU heatsinks,
reducing the helpful top-down airflow most stock cooler units provide over the
components surrounding the CPU socket.

For those concerned about this issue, down-blowing heatsinks are better, though
they generally do not cool the processor as effectively, partly because they
do not blow exhaust out toward the back of the system. An ideal top-down cooler
would provide improved socket cooling without sacrificing much in the way of
CPU cooling proficiency.

Enter the Scythe Grand Kama Cross, a larger version of the Kama Cross, a modestly
sized cooler with only 3 copper heatpipes and a 100 mm fan. The Grand version
is much larger, featuring four heatpipes with airflow provided by a 140 mm Slip
Stream fan. It is unusual looking with the heatpipes curving inward so that
the ends cross each other in a “X” formation. The aluminum fins around
the heatpipes are tightly spaced, angled to direct airflow around the socket,
and surprisingly short, particularly at the ends. The total area of the fins
is lower than usual for a heatsink of this size.


The Scythe Grand Kama Cross box.

 


The Grand Kama Cross.

While Scythe has introduced hard mounting systems for some of their heatsinks,
the Grand Kama Cross, despite weighing 750 grams, ships with S478, AMD, and
LGA775/1156/1366 mounting frames that utilize stock mounting mechanisms. On
the Intel side, not only do you have to deal with push-pins, but for LGA1156,
the pins have to be slid halfway between the LGA775 and 1366 positions. There
is nothing to lock the push-pin in place, which can result in a mounting that
is off-center. The only good thing about these frames is they can be rotated,
which is useful for the Grand Kama Cross since one side is much wider than the
other. If the heatpipe ends are arrayed vertically, it could interfere with
the power supply in many ATX tower cases.


Accessories.

 

Scythe Grand Kama Cross: Key Features
(from the product
web page
)
Feature & Brief Our Comment
Top Mount Fan
By pointing the airflow of the fan towards the motherboard, Chipsets and
MOS-FETs on VR modules can be cooled simultaneously.
Blowing down on the motherboard has its
advantages, but this usually results in poorer CPU cooling compared to heatsinks
that blow out the side.
Slip Stream 140 mm PWM Fan
By applying the new SLIP STREAM140 fan, wider area of components on the
motherboard can be cooled compared to 120mm fans while keeping low noise
and high cooling ability for the CPU.
120mm Slip Streams perform well and have
excellent acoustics. The Grand Kama Cross uses a large 140 mm PWM model.
4-Way Mounting
4-Way (direction) mounting is available. This allows you to configure the
optimized airflow direction inside your chassis without and restrictions.
Like many Scythe coolers, the mounting
frame is secured from the bottom with a square hole configuration, allowing
it to be freely rotated.

 

Scythe Grand Kama Cross: Specifications
(from the product
web page
)
Model Name Grand Kama Cross CPU Cooler
Model No SCKC-2000
Compatibility Intel®:
Socket 478
Socket T / LGA775
Socket LGA1156
Socket LGA1366

AMD®:
Socket 754
Socket 939
Socket AM2
Socket AM2+
Socket AM3

Dimensions 177 x 140 x 137 mm /
6.97 x 5.51 x 5.39
in
Fan Dimensions 140 x 140 x 25 mm /
5.51 x 5.51 x 0.98 in
Noise Level 9.6 ~ 24.7 dBA
Air Flow 27.2 ~ 69.93 CFM
Fan Speed 500 ~ 1,300 rpm (± 10%)
Weight 750 g (26.46 oz)
Material of Base Plate Nickel-plated copper

PHYSICAL DETAILS

The Grand Kama Cross is composed of 4 copper heatpipes, and 72
short aluminum fins. It measures 177 x 140 x 137 mm (W x D x H) and weighs about
610 grams, 750 grams with the stock fan and bolts.


The heatpipes are twisted like a pretzel, with the ends curved to cross
over in opposite directions. The fin mass is also strange, cut into a
series of short, staggered inclines at the top, tall near the center,
and short at the edges. The portion of the fins closest to the heatpipes
are angled to send airflow to either side of the CPU.


Though a very wide heatsink, the Grand Kama Cross is only 13.7 cm tall,
and the fins are high off the ground so it is unlikely they will interfere
with board components/heatsinks.


The fins are 0.38 mm thick and spaced 1.66 mm apart on average. The fan
is bolted to a pair of metal “L” brackets attached to the ends
of the heatpipes — this may exacerbate vibrational effects from the
fan.


The bottom.


The heatpipes are soldered to a flat, nickel-plated copper base with a
good degree of polish.


Installed on our LGA1366 motherboard using push-pins. In this orientation,
the heatsink does not overhang the motherboard edge and at the back, there
is about one inch of clearance to the outside edge of the back panel connectors.

TESTING

Before thermal testing, we took some basic physical measurements.

Approximate Physical Measurements
Weight
610 g
750 g with fan and bolts
Fin count 72
Fin thickness
0.38 mm
Fin spacing
1.66 mm
Vertical Clearance
51 mm (from the motherboard
PCB to the bottom fin)
Horizontal Overhang (+/-)
18 mm (far edge
of the heatsink to the top edge of the motherboard PCB)

 

Comparison: Approximate Fin Thickness & Spacing
Heatsink
Fin Thickness
Fin Spacing
Scythe Ninja 2
0.39 mm
3.68 mm
Thermalright HR-01 Plus
0.45 mm
3.15 mm
Noctua NH-U12P
0.44 mm
2.63 mm
Noctua NH-C12P
0.47 mm
2.54 mm
Thermolab Baram
0.44 mm
2.52 mm
Noctua NH-D14
0.43 mm
2.33 mm
Prolimatech Armageddon
0.51 mm
2.08 mm
Prolimatech Megahalems
0.50 mm
2.00 mm
Zalman CNPS10X Quiet
0.40 mm
2.00 mm
Xigmatek HDT-S1283
0.33 mm
1.96 mm
Scythe Kabuto & Zipang 2
0.34 mm
1.94 mm
Scythe Mugen-2
0.31 mm
1.89 mm
Cooler Master V8
0.30 mm
~1.85 mm
ZEROtherm Nirvana
0.43 mm
1.82 mm
ZEROtherm Zen
0.37 mm
1.80 mm
Titan Fenrir
0.36 mm
1.78 mm
Cogage TRUE Spirit 1366
0.40 mm
1.70 mm
Scythe Grand Kama Cross
0.38 mm
1.66 mm
Cooler Master Hyper 212 Plus
0.43 mm
1.54 mm
Zalman CNPS10X Extreme
0.42 mm
1.50 mm
Thermalright Ultra-120
0.45 mm
1.42 mm

Testing was done on our
new i7-1366 heatsink testing platform
. A summary of the test system
and procedure follows.

Key Components in Heatsink Test Platform:

  • Intel Core i7-965 Extreme
    Nehalem core, LGA1366, 3.2GHz, 45nm, 130W TDP.
  • Asus
    P6X58D Premium
    ATX motherboard. X58 chipset.
  • Asus
    EAH3450 Silent
    graphics card.
  • Intel
    X25-M
    80GB 2.5″ solid-state drive. Chosen for silence.
  • 3GB QiMonda
    DDR3 memory. 3 x 1GB DDR3-1066 in triple channel..
  • Seasonic X-650 SS-650KM
    650W ATX power supply. This PSU is semi-passively cooled. At the power levels
    of our test platform, its fan does not spin.
  • Arctic Silver
    Lumière
    : Special fast-curing thermal interface material, designed
    specifically for test labs.
  • Nexus 120 fan (part of our standard testing methodology; used when
    possible with heatsinks that fit 120x25mm fans)

The system is silent under the test conditions, except for the CPU cooling
fan(s).

Normally, our reference fan is used whenever possible, the measured details
of which are shown below.

Reference Nexus 120mm fan
Anechoic chamber measurements
Voltage
SPL@1m
Speed
12V
16 dBA
1100 RPM
9V
13 dBA
890 RPM
7V
12 dBA
720 RPM

Measurement and Analysis Tools

  • Extech 380803 AC power analyzer / data logger for measuring AC system
    power.
  • Custom-built, four-channel variable DC power supply, used to regulate
    the fan speed during the test.
  • PC-based spectrum analyzer:
    SpectraPlus with ACO Pacific mic and M-Audio digital
    audio interfaces.
  • Anechoic chamber
    with ambient level of 11 dBA or lower
  • Various other tools for testing fans, as documented in our
    standard fan testing methodology
    .
  • SpeedFan,
    used to monitor the on-chip thermal sensors. The sensors are not calibrated,
    so results are not universally applicable. The hottest core reading is used.
  • Prime95,
    used to stress the CPU heavily, generating more heat than most real applications.
    8 instances are used to ensure that all 4 cores (with Hyper-threading) are
    stressed.
  • CPU-Z,
    used to monitor the CPU speed to determine when overheating occurs.
  • Thermometers to measure the air temperature around the test platform
    and near the intake of the heatsink fan.

Noise measurements are made with the fans powered from the lab’s variable DC
power supply while the rest of the system was off to ensure that system noise
did not skew the measurements.

Load testing was accomplished using Prime95 to stress the processor, and the
graph function in SpeedFan was used to ensure that the load temperature is stable
for at least ten minutes. The temperature recorded is the highest single core
reading. The stock fans were tested at various voltages to represent a good
cross-section of airflow and noise performance.

The ambient conditions during testing were 10~11 dBA and 21~23°C.

TEST RESULTS

Stock Fan

The 140 mm PWM Slip Stream is a 9-blade fan with a curved, but not quite round

Stock Fan Specifications
Manufacturer
Power Rating
2.64 W
Model Number
SM1425SL12LM-P
Airflow Rating
69.93 CFM
Bearing Type
Sleeve
RPM Rating
1300 RPM
Corners
Open
Noise Rating
24.7 dBA
Frame Size
120 x 120 x 25 mm
Header Type
4-pin PWM
Fan Blade Diameter
128 mm
Starting Voltage
~5.4 V
Hub Size
40 mm
Weight
140 g
Data in green cells provided by the manufacturer
or observed; data in the blue cells were measured.

housing, 120 mm fan holes, and a surprisingly small hub.

Stock Fan Measurements
Voltage
Speed
SPL @1m
12V
1310 RPM
28 dBA
10V
1090 RPM
21 dBA
9V
970 RPM
17 dBA
8V
820 RPM
14 dBA
7V
680 RPM
11~12 dBA
Measuring mic positioned 1m at diagonal angle from
the intake side of the fan.
Ambient noise level: 11 dBA.

The stock fan was previously tested when we reviewed the Prolimatech
Armageddon
, and the noise level was very similar with the exception
of a 2 dBA increase at 12V which may have been caused by the metal frame to
which the fan is mounted. Thankfully, this is not a serious issue since we consider
both 26 dBA and 28 dBA too loud for serious consideration in a quiet PC.

The fan exhibits some minor bearing chatter, and is a little whiny at full
speed, but other than that, its acoustics are excellent throughout its range
like other members of the Slip Stream family. The fan is really only too loud
at 12V. At 10V, the measured noise level is high at 21 dBA, but all you really
hear is turbulence. It undervolts well, becoming inaudible at around 7V.


The Scythe 140 mm fan measured 17 dBA@1m at 9V. Frequency analysis revealed
practically no tonality.

Cooling Results

Scythe Grand Kama Cross w/ stock 140 mm fan
Fan Voltage
SPL@1m
Temp
°C Rise
12V
28 dBA
59°C
38
10V
21 dBA
61°C
40
9V
17 dBA
62°C
41
8V
14 dBA
65°C
44
7V
11~12 dBA
70°C
49
Scythe Grand Kama Cross w/ ref. 120 mm fan
12V
16 dBA
66°C
45
9V
13 dBA
73°C
52
7V
12 dBA
78°C
57
Load Temp: Prime95 for ~10 mins.
°C Rise: Temperature rise above ambient (21°C) at load.

The Grand Kama Cross performed admirably considering that it is a top-down
cooler. With the stock fan at fairly quiet 17 and 14 dBA levels, the thermal
rise above ambient was only 41°C and 44°C, respectively. At 11-12 dBA
the fan becomes almost inaudible, and the temperature increased by an additional
5°C. This would put the in-case temperature of the CPU at ~80°C or higher,
which is probably too high for most users’ comfort… but it may be a perfect
acceptable setting if you know you will rarely push the CPU as hard was we do
in our testing (100% load on all cores for >20 minutes continuously.)

Our Nexus 120 mm reference fan is apparently too small to be as effective as
the stock 140mm fan, allowing the CPU to get 4°C hotter at 12V/16 dBA than
the stock fan at 9V/17 dBA. As the reference fan’s speed was slowed, the difference
became more apparent. With both fans at 7V, the stock fan was slightly quieter
and a very significant 8°C cooler. It’s clear that the large stock fan is
essential to the Grand Kama Cross’ success.

Comparison Chart

°C rise Comparison
Heatsink
Nexus 120mm fan voltage /
SPL @1m
12V
9V
7V
16 dBA
13 dBA
12 dBA
Prolimatech Megahalems
38
41
44
Noctua NH-D14
38
42
45
Noctua NH-U12P
39
42
44
Scythe Mugen-2
39
42
45
Cogage TRUE Spirit 1366
40
42
45
Prolimatech Armageddon
40
42
46
Zalman CNPS10X Quiet
40
43
46
Thermalright U120 eXtreme
40
43
48
Cooler Master Hyper 212 Plus
41
44
48
Scythe Grand Kama Cross
(Stock 140 mm fan)
17 dBA (9V)
14 dBA (8V)
11~12 dBA (7V)
41
44
49
Thermalright U120
42
45
49
Titan Fenrir
43
46
50
Noctua NH-C12P
43
47
51
Zalman CNPS10X Extreme
43
47
53
Zalman CNPS10X Flex
45
50
54
Cooler Master V8
46
50
54
Scythe Grand Kama Cross
45
52
57
Scythe Kabuto
51
53
60

The large, efficient stock fan of the Grand Kama Cross propels it past the
Noctua NH-C12P as
our best top-down cooler, and challenges some of the better tower heatsinks.
When paired with our reference 120 mm fan, it drops far down in the chart, but
still dishes out a severe beat-down to the Scythe
Kabuto
.

It may not be as effective when it comes to cooling the components around
the socket though, as the height of the heatsink without the fan is 112 mm,
compared to 91 mm for the Noctua NH-C12P. The Noctua’s fan, though smaller,
is closer to the PCB by almost an inch, and the closer proximity may have an
impact on cooling effectiveness of the motherboard components.

MP3 SOUND RECORDINGS

These recordings were made with a high
resolution, lab quality, digital recording system
inside SPCR’s
own 11 dBA ambient anechoic chamber
, then converted to LAME 128kbps
encoded MP3s. We’ve listened long and hard to ensure there is no audible degradation
from the original WAV files to these MP3s. They represent a quick snapshot of
what we heard during the review.

The recordings are intended to give you an idea of how the product sounds in
actual use — one meter is a reasonable typical distance between a computer
or computer component and your ear. The recording contains stretches of ambient
noise that you can use to judge the relative loudness of the subject. Be aware
that very quiet subjects may not be audible — if we couldn’t hear it from
one meter, chances are we couldn’t record it either!

The recording starts with 5~10 second segments of room ambiance, then the fan
at various levels. For the most realistic results, set the volume so that
the starting ambient level is just barely audible, then don’t change the volume
setting again.

FINAL THOUGHTS

We were skeptical at first about how well the Scythe Grand Kama Cross would
perform due to its relatively modest surface area and tightly spaced fins—
this combination typically spells lower performance for quiet CPU cooling. These
fears proved to be unfounded as the GKC performed very well on our testbed,
even rivalling some very successful tower coolers. The included 140 mm Slip
Stream fan is probably the best stock fan that ships with any heatsink, both
in terms of performance and acoustics. Our only criticism is the traditional
mounting methods used for this big heatsink. A metal backplate with bolts is
strongly recommended for a cooler of its size and weight. We wish Scythe would
retool the mounting systems for all its big coolers.

The Grand Kama Cross delivered the best CPU cooling for a down-blowing heatsink
on our LGA1366 test bed to date, but the Noctua
NH-C12P
may be the better top-down cooler overall. Though more expensive
and equipped with an inferior fan, the Noctua heatsink mounting system is immeasurably
better and its shorter stature puts its fan closer to the socket and surrounding
components by almost an inch. Of course, the Noctua is also most costly. If
you care only about CPU temperature, the Grand Kama Cross is the better choice
of the two, but budget tower coolers like the Cogage
TRUE Spirit
or Cooler Master
Hyper 212 Plus
are also viable alternatives.

Scythe Grand Kama Cross
PROS

* Excellent stock fan
* Good performance
* Well priced

CONS

* Traditional mounting schemes
* A bit tall for a top-down cooler

Our thanks to Scythe
Co., Ltd.
and for the Grand Kama Cross heatsink sample.

* * *

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Titan Fenrir & Coolermaster Hyper 212 Plus: Direct Touch Revisited
Corsair Hydro H50 CPU Water Cooler
Prolimatech Armageddon & Coolermaster
V8 CPU Coolers

Cogage TRUE Spirit
& Zalman CNPS10X Quiet CPU Coolers

SPCR’s 2010 CPU Heatsink
Test Platform [UPDATED: 10 April 2010]

Zalman CNPS10X Flex CPU Cooler

* * *

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