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Plumbing Basics, Part 3

The ins and outs of plumbing

by Julian Edgar

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At a glance...

  • Sourcing large diameter hose
  • Clamps
  • Valves
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This article was first published in 2005.

So far in this series we’ve looked at smaller diameter plumbing – hose, T-pieces, barbed fittings and lots of different types of valves. This week, in the last of the series, we’ll up-size to blow-off valve, turbo and supercharger plumbing.

The Glitz

It’s possible to spend an enormous amount of money on intercooler and turbo plumbing. Silicone hose, polished TIG-welded aluminium mandrel-bent tube – if you’re using a secondhand intercooler and turbo, the plumbing can cost more than the rest of the system! On the other hand, it’s also possible to have good quality, effective plumbing that doesn’t have to cost a huge amount. Or, of course, you can also pick a route somewhere in between.


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The easiest way of obtaining suitable hose for intercooler and turbo plumbing is to visit a trucking supplies company. If the turbo plumbing is 2 inch or under, the trucking supplies company will have straight rubber hose and bends in their radiator hose section. Bare 45- and 90-degree rubber bends are available, or more complex shapes can be bought as full radiator replacement hoses.

If you’re yet to lay out the plumbing route through the engine bay, it’s well worth bending a long piece of wire into the approximate shape the hoses will need to follow and then visiting a truck wrecker or parts supplier to see if a pre-moulded hose of the right shape is available. Moulded rubber hoses look good and can be quite cheap to buy (compared with custom plumbing, anyway!). If a secondhand hose looks a bit grey, use some car external black trim rejuvenator on it.

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Other advantages of moulded rubber hoses over fabricated pipework include the use of less clamps (because extra rubber sections aren’t needed to allow for the engine movement) and that lower precision is needed in the shape of the tube – ie the hose ends can be moved a bit relative to one another.

Larger diameter hoses (say for the turbo inlet) are also available from truck suppliers. In this case they’re used for the inlet side of the truck engine – rubber bends and hose with diameters all the way up to a huge 6 inches are commonly available! In addition, you’ll find rubber adaptors that allow you to increase or decrease pipe sizes – eg to change from 2½ inch to 3 inch. However, ‘step’ changes like this aren’t good for flow, so should be avoided.

Another one to avoid is convoluted tube. Unless you go well up in size over what would normally be required, convoluted tube can be quite restrictive. If the tube doesn’t have to move a lot in service (like a brake duct needs to, for example), then convoluted tube should not be used.

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Blow-off valves are often harder to cater for  – they use slightly odd hose diameters. However, radiator hoses can again come to the rescue – this time off smaller cars. As with the intercooler hoses, the moulded shape of these can be used to advantage, making the BOV look really well integrated.

Industrial suppliers also stock all these hoses, but depending on where you live, they can be harder to locate than truck parts suppliers.

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If you’re worried about durability of running car and truck radiator hoses in turbo applications, rest easily.

Unless you’re using ultra-high boost pressures (like 25 psi), the radiator hoses and bends will easily handle the pressure – after all, pretty well all coolant systems run up to 15 psi.

The temperature of the air passing through them also generally doesn’t cause problems – although if you have an extremely inefficient turbo or supercharger pumping air out at 150 degrees C, the hose will slowly degrade internally. In this situation you can instead use expensive silicone hose for just that part of the system, or every year or two simply replace the rubber hose that’s subjected to the very high temps.


There’s no problem using worm-drive clamps (of the sort we discussed in Plumbing Basics, Part 1) on turbo hoses. Pretty well every factory turbo car has these clamps and if the hoses continually blow-off when using worm-drive clamps, it’s more likely the case that you’ve left insufficient ‘give’ in the plumbing to cater for engine movement or the hose is too large for the pipe to which it is connecting.

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However, if you want to go more elaborate than worm-drive clamps, T-nut clamps are also available – again a cheap source of supply is a truck parts shop. However, this type of clamp needs to be accurately sized for the hose to which it is being fitted - that is, the adjustment range is much less than for a worm-drive clamp.  So if buying this type of clamp, always take along a sample piece of the hose.

One easy way to stop hoses coming loose when they’re attached to metal pipe plumbing is to take the plumbing along to an exhaust shop and get the guys there to use their hydraulic bending machine to flare the ends of the pipes very slightly. An increase in diameter of only ~2mm will stop a properly clamped rubber hose from coming off, even at high pressure. But don’t flare the pipe too much or you’ll never get the hose onto it!


We covered all sorts of valves in Plumbing Basics, Part 2 of this series, but there are a couple of applications unique to larger diameter plumbing.

The first is in idle speed control. If you have performed an engine swap or made a radical engine management or camshaft change, you may find that the car won’t idle satisfactorily. It may be too slow in idle speed, or it may be too fast. The ECU is trying to change the speed, but the bypass solenoid (or stepper motor) doesn’t have sufficient control.

An easy way to increase the idle speed in this situation is to place a second bypass around the throttle and use an adjustable valve within it. A needle valve will allow very fine adjustment but in the larger size that is needed in this application, a ball valve will be a lot cheaper and probably still have sufficient adjustment resolution.

If the idle speed is too high, and an external bypass is used for idle speed control, a valve placed in the feed to the idle speed control solenoid will reduce the amount of air it flows, dropping idle speed.

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The other type of valve unique to large diameter plumbing is an electronically-controlled blow-off valve. Solenoid valves are available in super-large sizes like ¾ inch and 1-inch, and can be used as extremely effective blow-off valves. See The All-Electronic Blow-Off Valve! for more on this approach.

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If you’re after an enormous quantity of hoses, cast elbows and adaptors, go along to a large wrecker and be prepared to get your hands dirty. Wreckers – especially Japanese importing wreckers – often have a few drums full of such bits and pieces. But before you leave home, make sure you know the exact internal diameters that you need and have a good idea of what bend radii and lengths are needed. Take a pair of calipers with you to allow quick and easy measurements – the hoses often have unique (and odd!) internal diameters, rather than just for example 2 inch, 2¼ inch, etc.

Series Conclusion

So there’s a brief overview of cheap and easy plumbing solutions for cars – from brass fittings through to truck radiator hose, from adjustable needle valves to electric solenoid valves, it’s all durable and available at good prices.

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