If you’re fitting an intercooler at home, you’ve got a number of options when
it comes to the plumbing. You can use stainless steel, mild steel, aluminium –
or copper. Copper? Yes, one approach that’s rarely done is to use preformed
plumbing bends and tube made from copper. So what are the advantages and how
does it all come together?
DIY Intercooler Plumbing
The most common approach in DIY intercooler plumbing is to use mild steel
exhaust tubing. This is easily bought in preformed bends and can be welded
together as required. Normally, the home tinkerer cuts and grinds until the
bends and short straights form the right overall shape, tapes it together, and
then takes it to a welder. Another option is to use pre-formed bends in
aluminium tube – and much the same process as with steel is followed. More
difficult to work with - but potentially looking the best – is stainless steel
pipe like that shown here. (Incidentally, polished stainless steel bends can
often be bought from scrap metal and secondhand machinery dealers.)
However, while taking any of these approaches seems great in theory, in
practice it’s much harder than it looks. Firstly, without a big saw (eg a
friction disc cut-off saw) it’s difficult to cut the tube squarely. (You need to
be a genius to cut 2-inch tube square with a hacksaw!) As a result, lots of
filing and grinding is usually needed before the sections of tube will match-up
Secondly, when you take the taped-together assembly to a welder, it’s
imperative that the bits and pieces get welded together with exactly the right
rotational orientation. For example, if a join has rotated even slightly, you
might find that at the other end of the assembly the pipe shape misses the
required cut-out in the car’s sheet metal by inches! Have two or three joins
that aren’t lined-up perfectly in the welding and the whole plumbing job can be
a disaster. And because the bits of pipe are held together with just butt
joints (ie they don’t slide into each other), such a rotation at the joins can
easily occur in the distance between your place and the welder.
However, there is a way of putting together intercooler plumbing which is
much more likely to be successful – use copper.
We’re used to seeing lots of plumbing bends in hardware stores made from PVC
plastic pipe but prior to the widespread use of plastic, all these bends were
made from copper. And copper pipe bends are still available from plumbing supply
Like plastic pipe bends, you can get a wide variety of sizes – including 40mm
(~1.5 inch), 50mm (~2 inch), 65mm (~2.5 inch), 80mm (~3 inch) and 100mm (~4
inch). Both short radius and long radius bends are also available. (Short radius
bends use a radius the same as the pipe diameter, while long radius bends use a
radius about 50 per cent bigger than the diameter.) Bends are available in 45
and 90 degree angles.
Like plastic pipe bends, these copper bends are designed to slide into the
appropriately sized pipe. So for example, a 90-degree 50mm bend has two socket
ends into which 50mm copper pipe snugly fits. This means the complete
intercooler pipe system can be semi-rigidly constructed before final brazing is
The bends are also pretty good in internal shape, with all the short-turn
radii being smoothly curved and the full internal diameter being maintained
through the bends. However, when the pieces of straight pipe are pushed into the
bend’s sockets, the inner surface isn’t as smooth as is obtained with (say)
TIG-welded exhaust tube.
Another potential advantage of copper is that it will better conduct the heat
through the walls of the tube – so the ‘hot side’ plumbing on its way to the
intercooler will shed some of the heat. Of course, the opposite will also occur,
so the ‘cold side’ tube should be insulated so heat isn’t transferred from the
engine bay back into the cooled intake air.
And another thing: with this intercooler plumbing, corrosion will never be a
The cost is lower than you might first think. In 50mm tube, right-angle,
short radius bends cost AUD$6.50 each, with 45-degree bends AUD$6 each. Again in
50mm diameter, copper tube costs AUD$26 a metre – cheaper in fact than a metre
of 2-inch mild steel exhaust tube that on the same day cost me AUD$30!
Finally, because copper is softer than mild steel, it’s possible to put
dimples in the pipe and bends to miss critical components – something which may
be necessary in tight engine bays.
If flanges are required in the system, it’s easy to have them cut from steel
and have the copper plumbing brazed or silver soldered to the mild steel. For
maximum strength, the copper pipe or fitting should pass through the flange,
being brazed on both the inside and outside of the flange. The inside can then
be tidied-up with a round file.
So you have a bunch of 45 and 90-degree copper bends and some straight copper
pipe. What’s next?
If there’s plenty of room, it’s just a case of cutting the pipe to length (to
improve your chances of keeping the edge square when using a hacksaw, wrap a
piece of electrical tape around the pipe and cut along that), and assembling the
bends and pipe by pushing them together. The ‘fit’ is quite tight so the pipe
and bends will stay assembled unless you deliberately pull them apart.
If two bends are being placed directly one after the other and clearances are
tight (and when aren’t they?), the expanded ‘socket’ ends of the bends can be
cut off short. If you leave enough of the sockets that the joining pipe will
still be held in place, this will squeeze up the assembly with no downsides. If
clearances are too tight to allow even that, the bend sockets can be completely
cut off – although then you’re back to holding together butt joints until you
can get to a welder.
In some cases, for example if you cut off the socket of one of two bends
being assembled closely together, the assembly won’t want to stay together. In
this case, drill some small diameter holes through the edges of the sockets and
use self-tapping screws to temporarily hold the assembly together. After the
joints have been tack-welded, the screws can be removed and the holes
Talking about welding, the strongest approach is to silver-solder the joints
together. Less strong but still plenty durable is to braze the joints, and not
as strong (but quickest) is to soft-solder the joints. Soft-soldering can be
carried out at any radiator repair shop, while brazing and silver-soldering are
normally done by a welder. Note that these latter processes can be quite slow,
so you might want to get a quote before work is started.
Compared with using rubber hose, a major advantage of using slip-together
copper pipe and bends is the ease with which additional fittings can be added.
For example, a blow-off valve exit or boost pressure measuring point can be
easily incorporated by simply having a section of smaller diameter tube welded
at right-angles to the copper plumbing.
Copper plumbing is (obviously!) inflexible. So unless the intercooler is
being mounted on the engine, the copper plumbing should always include a section
of rubber hose to allow the engine to move relative to the body. This can take
the form of a rubber elbow or straight section of hose.
When building intercooler plumbing, in many case a change in diameter needs
to be catered for. This might be at the connection from the turbo plumbing to
the intercooler, or where the intercooler plumbing reaches the throttle body. An
easy and cheap way of making up an adaptor is to have an exhaust shop expand a
short section of mild steel pipe that matches the smaller diameter, so that the
other end matches the larger diameter. Silicone and rubber hose adaptors are
also available to cater for diameter changes.
For someone building intercooler plumbing at home, copper tube and fittings
have some major advantages. The bends are high quality and are available in
tight radii, the plumbing can be easily assembled and held together until the
assembly is taken to a welder, and the price of the pipe and bends are quite
low. It’s also easy to add boost and/or pressure measuring points. The
downsides? Well, if lots of fittings are used, the welding costs can soon add
up; and if you’re working in a very tight space, a moulded rubber hose gives you
more flexibility. Finally, after it has been welded, the copper is quite soft,
so you need to be careful not to dent it.
So it depends on the application whether copper tubes and fittings have major
advantages over lots of bits of rubber and hoseclamps. Perhaps a combination of
both is best of all...
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