Copper Intercooler Plumbing

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 perfectly.

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.

Using 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 businesses.

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 undertaken.

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 problem!

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.

Flanges

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.

Doing it

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 welded-up.

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.

Diameter Changes 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.

Conclusion

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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