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
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.
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.
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.
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.
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
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.
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.
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.
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