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It seems that due to the cost of new fabricated intercoolers, a lot of
people are looking for a cheap alternative. However, as the old
saying goes, 'you only get what you pay for' and the same applies to
intercoolers. There are significant differences in intercoolers,
not only in core construction (bar and plate or tube and fin), but also
their design (especially tank design).
There is a reason for the
cost involved in buying a new intercooler (whether it be ARE or another
company), and they do offer advantages over other options especially
truck intercoolers.
Bar and Plate or Tube and Fin?
Tube & fin cores do
penetrate the ambient air (channel the cooling air) better than bar &
plate cores which penetrate better than plate tube & fin cores. Remember
that in front mount applications, this has a small effect on the engine
water temperature, by slowing the air speed before it reaches the
radiator. This is because the rounded leading edge of the tube & fin
tube parts the air with less turbulence than the square leading edge of
the bar & plate tube, which parts the air with less turbulence than the
"W" shape of the tube & fin tube. The following drawings illustrate the
turbulence caused by the three tube shapes.
Tube and Fin
Bar and Plate (below)
Plate Tube and Fin (below)
Tanks
Square edged tanks are frowned upon by
performance conscious enthusiasts for two reasons:-
1) A square edge concentrates stresses
along that fold, which, depending on several factors, will shorten the
life of the tank to a some extent. It's surprising the number of small
weeps that can go undetected for months, especially if the turbo seals
are good, resulting in a loss of economy/performance. This applies more
to a sheet metal tank than cast tanks, due to their thinner wall
construction.
 
Square edged intercooler tank and
resulting flow
Better designed intercooler tank and resulting flow
2) Most importantly is that the square
edged tanks hurt air flow & increase "static" pressure drop. The intake
charge does not want to make a sharp turn with the majority of the air
taking a radiused path out off the edge, causing some of the air to eddy
back around through an elongated 360 degree tumble. This causes friction
with both the wall surface & the following air, really hurting flow
figures.
A few factors should be remembered with
air flow. A street car is not in high boost that much of the time
(maybe20% max. or no licence, no tyres!), and for possibly 20% of the
time in vacuum, with maybe another 30% at less than 5psi boost, so the
engine operates as a naturally aspirated engine for approximately 40% of
it's life.
Now, how many hundreds of hours a year do
the Group A Supercar teams spend on the flow bench trying to find even a
half a percent increase in flow? A square edge tank can easily cause a
20 percent drop in flow, in vacuum !! Some people confuse the result of
poor tank/pipe design with turbo lag, when it actually may have little
to do with the turbo's performance.
This has been reinforced with our
Air/Water intercooler R&D. program, where much shorter/straighter pipe
lengths are used (reduced turbo lag). A crisper throttle response with
increased "driveability" can actually be felt driving the vehicle, also
very important in Rally, Hillclimb, Jet boat, type competitions.
The importance of squared tanks
exponentially decreases with boost pressure increases. If you see a car
at the drags that runs 35 plus psi, with square tanks on it's
intercooler, don't worry about it after the car has launched & is
revving out as power loss is minimal ( maybe 3%), but if the engine
could not spool up quickly, or needs nitrous to spool up, then the tank
shape plays a very definite part in this problem, with Rotary engines
seemingly affected more than 4 cylinder engines.
Can an intercooler be too big?
In street driven applications, an
intercooler can definitely be too big, not for 'attitude', but for
maximum performance. It is not an argument to say that Joe Blow's RX2
runs 9.6 @ 132 with a monstrous intercooler because that car may run 9.4
@ 134 with an intercooler that is engineered very close to the overall
requirements of that combination. The same may be said for Fred Nerks
TX3 that runs 13.8 @ 100 with his headlight to headlight monster
intercooler jumping out of the grille. The car may run 13 flat @ 108
with a proper engineered setup. This is because if a 13,500 cu. cm. core
drops the intake temperature to 40 degrees @ 1.3 psi. "static" pressure
drop, a 8,550 cu. cm. core may drop the temperature to 41 degrees @ 0.82
psi "static" pressure drop, which will produce more power.
The closer to ambient temperature the
intake charge gets cooled to, the exponentially higher the internal
surface area of the core is needed, also exponentially increasing the
friction (drag) of the air in the larger core.
Make an effort to suss out the best
overall intercooler & pipework for your car, usage & driving style. It
may make a worthwhile gain, possibly at less cost!
Intercooler Maintenance
An intercooler that has been in service
for a couple of years will definitely provide more cooling if it is
cleaned properly. That is, soaked in a degreaser bath to remove the
interior oil film that has accumulated (which may be ever so thin with a
new turbo), then power flushed with water. The exterior fins should
sprayed with a proper aluminium acidic cleaner to remove the surface
oxidation that will have formed. Both the oil film & oxidation inhibit
the transference of heat to the ambient air.
If not sure of the proper procedure &
products to use, we strongly recommend having this done by a
professional business.
Please see the below picture, which is a 9 month old intercooler that
was soaked in a water based degreaser mixed with kero. The caustic base
of the degreaser attacked the alloy & rendered the core completely
useless, a new core being the only alternative - expensive mistake.
Specific acid cleaners must be used on the external cooling fins as the
average thickness is only 0.08mm - that's paper thin. Any bent over fins
should be straightened so full air flow is allowed through the core.
Last word. Intercooling a forced induction intake charge is a
compromise. We direct all our energies at minimising the negative
compromises & maximising the positive compromises!
(insert ill-cleaned intercooler picture
here)
Truck Intercooler Cores
There are numerous
differences between a 'truck intercooler' and an intercooler fitted into
a performance car application. However, 'truck intercoolers' is a
broad term and does not sufficiently categorise the product. Just
like other types of products, truck intercoolers come in both bar and
plate and tube and fin design. However, due to their specialised
application truck intercoolers have a noticeably courser internal fin or
external fin pitch (depending on whether tube and fin or bar and plate),
than their cousins fitted into normal performance car applications.
This means that although a
new truck core can be used in performance applications, the core surface
area/volume must be large enough in proportion to that of a standard
'performance core', because although it will give good temperature drop
it will be at the cost of a medium/ high "static" pressure drop.
A truck intercooler core has
to be larger because as with any intercooler, the heat from the intake
charge is dissipated by contact with the surface of the interior walls
(fins or extrusions), and then is transfers through the thickness of the
exterior wall to the surface of the exterior fin, and is then
transported away by the passing ambient air.
The larger volume of a truck
intercooler has three main drawbacks:-
1) Higher 'static' pressure drop
2) Increased 'turbo lag'
3) Higher engine water/under bonnet temperatures - in front mount
applications as the large truck intercooler blocks more of the flow
through to the radiator.
Therefore, if money is a
major issue than new truck cores in a performance car are a viable
BUDGET
alternative, especially if tanks can be fitted at "mates rates"!
Used Truck Intercooler Cores
It is our opinion that used
truck intercooler cores should not be used in a performance car.
Using a used truck intercooler core is a huge gamble, are you prepared
to risk the welfare of your engine because of a cheap intercooler.
Why put a $100 core in front of a $2000+ engine?
Because most truck
intercooler cores fit straight into a performance car application, they
are usually modified. During this modification process, whether it
be when the old tanks are being cut off, or when the core is being cut
down in preparation for welding tanks on, swarf and fillings can get
lodged in the core, some of which can be up to 600mm in length and can
be imposible to blow or clean out. The result is that they
dislodge days or weeks later, after working their way through the
intercooler tubes and intake piping and end up passing into the engine.
I'm sure you can imagine the result of that!?
Another point is that bar &
plate and finned tube cores are much, much harder to clean any solid
particles out of as they get trapped in the fins & have to "travel"
through the length of the tube, interestingly, the exact same reason why
per sq. cm., these cores dissipate heat better, but at a higher "static"
pressure drop.
Used truck cores in a
performance car are a stupid desperation alternative.
Short
Glossary (for a our full edition
click here)
* Static pressure drop - The measurement
of the drop in pressure of the air travelling through the core, friction
or 'parasitic drag' measured on a flow bench (of capable capacity) at
ambient temperature.
* "Dynamic" pressure drop - The
measurement of the drop in pressure of the air travelling through the
core, friction or 'parasitic' drag plus the drop in pressure caused by
the cooling of the intake charge (closer molecular structure of the
particles resulting in a denser, smaller volume exiting) due to the
mechanical design of the intercooler, or in more engineering
terminology, thermal matrix heat exchanger!
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