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DIY Intercooler Plumbing

Getting a new intercooler connected

By Julian Edgar

Click on pics to view larger images


This article was first published in 2011.

Upgrading the intercooler is one of the most common DIY modifications made to turbo cars. These days, with intercoolers available through eBay, it’s also a process with much greater flexibility (there are heaps of different sizes and shape ‘coolers available) and a modification that can be done much more cheaply than in the past.

But how do you plumb the intercooler into place? And what rules should you keep in mind when doing the work?

Let’s take a look.

Planning

One of the most important steps is planning where the pipe runs will go and what diameter they’ll be.

Normally there is a transition in size from the turbo outlet (smaller) to the intercooler intake (larger), and often another step up in size from the turbo outlet to the throttle body. Therefore, to say that you’ll use 3 inch (or 2½ or even 4 inch) plumbing is probably not the case: there will need to be a variety of sizes used.

The four initial dimensions to get sorted are:

- Turbo outlet diameter

- Intercooler inlet diameter

- Intercooler outlet diameter

- Throttle body diameter

Most factory turbo cars progressively increase the diameter of the plumbing between the turbo outlet and the throttle body - however this is hard to do when making your own. Instead, it’s common to adapt the plumbing coming out of the turbo to a larger size that connects to the intercooler, and then to use that same large size between the intercooler and the throttle. So the first step is to have a look at your car and decide on the diameters of plumbing that will be used in various areas.

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The next question is: is there room for this plumbing? It’s seldom the case that the factory has left space for large diameter plumbing to run around the engine bay – let alone get past the headlights and radiator to the front of the car. That means that two decisions need to be made: where will holes be cut (eg in inner guards) to let the new plumbing pass to the front of the car; or if the plumbing is reduced a little in size, can it be squeezed through existing gaps?

In a typical intercooling system by far the greatest restriction is caused by the intercooler itself, rather than the plumbing going to and from it. For example, without any downsides, you can typically use intercooler plumbing that is smaller than the intake to the airbox, and also a little smaller than the exhaust.

When cutting holes in bodywork, make the holes round without any nicks or rough edges. This reduces the likelihood of cracks starting from the holes. And always remember to look at the structural requirements of the metalwork that you’re cutting away!

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When planning pipe runs, aim to keep sharp bends to a minimum. For example, many people use 90-degree rubber or silicone elbows on the intercooler connections – but these are bad because they are very short radius (ie tight) bends that harm flow. It’s better to use larger radius metal bends and then make the connections to the intercooler with short straight sections of hose. In the same way, it’s better not to ‘hug’ the contours of the car’s metalwork but instead to just take the most smoothly-flowing paths.

Plumbing Types

There’s a myriad of ways of doing DIY intercooler plumbing.

Kits of Preformed Bends and Hoses

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You can buy intercooler hose kits that comprise steel, aluminium or stainless steel preformed bends; clamps; and silicone or rubber hoses and bends. The metal bends often have pre-formed lips on their ends, helping to hold the hoses in place.

However, for all but the simplest of installations, it’s very likely that the bends will not be quite right, so needing lots of bends, hoses and clamps. The end result can look a bit amateurish – did you really need to use that many clamps?! But the benefit of this approach is that no fabrication is needed.

Second-hand Hoses and Pipes

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If you live near a larger wrecker, especially one that imports used cars and parts from Japan, it’s likely that they’ll have a large assortment of used intercooler hoses, alloy and steel pipes. If you have a good idea of the required shape of the plumbing, you can pick out the required bits and pieces.

This approach is cheap (sometimes very cheap), gives you a lot of flexibility and requires few tools. And, despite also needing lots of clamps, the result can look quite professional with those original equipment parts integrated into the system.

Copper Fittings

This approach isn’t taken very often but it can be very effective, especially in lower power cars and where space is very tight.

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What you do is use off-the-shelf copper plumbing bends and tube that simply push together. You assemble the tubes into the right shapes, hold them together with tape or self-tapping screws and then take them to a plumber who cheaply brazes or silver solders them together.

You can get a wide variety of copper tube and bend sizes – including 40mm (~1.5 inch), 50mm (~2 inch), 65mm (~2.5 inch), 80mm (~3 inch) and 100mm (~4 inch).

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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 blow-off valve 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.

Mandrel Exhaust Bends and Tube

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Using off the shelf mandrel exhaust bends and exhaust tube gives you the greatest flexibility and at a fairly low cost. In addition, if well made, this plumbing can flow better than taking any of the above approaches. Mandrel bends are available in lots of diameters - from 2 inch to 6 inch!

However, to be successful with this approach it’s almost a necessity that you have a welder of some kind. You don’t need to do any more than tack the tubes together (so even an old arc welder can be used) but if you cannot rigidly hold the plumbing parts together before final welding, you’re almost sure to have major difficulties. (For example, many people tape the parts together and then take them to a welder. But the tape has to move only a fraction and you’ll find that at the other end of the plumbing you might have lost the 25mm of body clearance you had back home….and that means the tube no longer fits.)

In addition to a welder, you’ll need a friction cut-off saw or something similar – if you try to cut the tube with a hacksaw you’ll never get the ends square and so the alignment of the joins will be poor.

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The good news is that by taking this approach you can get the plumbing to go exactly where you want. Because you’re working in mild steel and using standard exhaust pipe sizes, adaptors (eg from 2½ to 3 inch) can be very easily and cheaply made by an exhaust shop, and pressure and blow-off valve fittings can be easily integrated. Adding brackets to hold the plumbing in place is also straightforward.

Some people worry about rust but if the inside of the tube is cleaned and then spray-painted, this is not a problem – in fact, some factory cars use mild steel intercooler plumbing.  If you want, you can get the tubes bead-blasted and then powder-coated – but this considerably adds to the overall cost.

Be wary about grinding back welds in steel intercooler plumbing. Because of the very thin walls, it’s easy to go a bit far with a linisher and find that the wall thickness has dropped to near-nothing – a potential boost blow-out or the starting point for a crack. If the welding is good, it shouldn’t need grinding-back.

You can also use stainless steel bends that can later be polished – however, for other than show installations, I don’t think the added difficulty in ‘working’ the material and the increased cost are worth it.

Bits and Pieces

Rubber vs Silicone

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If you’re on a budget or running really high boost (say over 20 psi) there’s nothing wrong with using plain ol’ rubber hose and elbows rather than the more expensive silicone equivalents. Rubber hose and elbows are available from industrial hose suppliers and these parts can be typically a quarter the price of buying silicone.

Clamps

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Look at factory turbo cars and you’ll often see just spring steel clamps used on the hoses. These rely on an exact fitting diameter (ie wall thickness of hose and outside diameter of steel tube) and so be wary of using these on self-made plumbing. However, expensive T-style clamps are unnecessary on small diameter (say 3 inch and under) plumbing not running very high boost pressures. Note that if you intend using T-style clamps you should provide greater hose overlap on the tube – these clamps are normally wider than traditional worm-drive clamps.

Flexibility

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It’s easy to forget that for a front-mount intercooler, the engine moves but the intercooler doesn’t! Ensure that there are sufficient flexible hose connections so that the engine can rock around (eg under launch) without tearing apart the intercooler plumbing, and also without transmitting excessive vibration to the bodywork from the engine.

Insulating the Return

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If the return pipe from the intercooler has a hot route through the engine bay to the throttle body, consider insulating it. You can wrap the pipe in aluminium foil tape (as here) or use silicone wetsuit style material (eg oven mitts chopped up for their high temp material).

Conclusion

Plan carefully, decide on the plumbing sizes you’re going to use, then select the type of plumbing that best suits your skills and tools. Then start work!

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