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When modifying NA cars I've always been advised to try and protect the intake from heat soak from the engine bay because the engine performs better with cooler air. This makes sense.

I now have a turbocharged car (Vauxhall Astra VXR) and it has a performance filter on it. Currently the filter is just sat in the engine bay, presumably sucking up lots of lovely hot air. Is there any benefit to reducing the heat soak here? Surely after the air has gone through the turbo it will be extremely hot anyway, reducing any benefit of cooler intake temperatures.

To clarify: I know that the air going into the engine should be as cool as possible. Is there any realistic benefit to having cooler air go into the turbo, given that it gets heated in the turbo?

  • Not a full answer, but I'll add that cooler air is more dense, so you get "more air" to the engine the denser the air is. – JPhi1618 Dec 20 '17 at 15:32
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Cooling air into the engine is always going to be a good idea, as heat soak reduces the power of an engine. A turbo does heat air, simply by compressing it, but you will still get a direct benefit from any cooling you can do, either before or after the turbo.

This is why any major performance improvements with a turbo tend to end up involving an intercooler.

You can also go for more low-tech solutions. Cladding on all your exhaust pipes will help, or moving the filter to the front of the engine bay, or even routing airflow from outside the car.

For my higher tune cars, an intercooler and an air-intake right at the front bumper gave significant performance benefits. I never got around to using cladding (however, seeing it used on a normally aspirated TVR showed me just how much of a difference it could make!)

  • I've added a bit of clarification around my question – James Monger Dec 20 '17 at 13:35
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The turbo will cause a change in pressure between the intake and the outlet so for the range of temperatures found under the bonnet / hood it won't affect the efficiency of the turbo itself very much.

However, as the other answers have pointed out cooler air into the intake will reduce the outlet temperature which is the main reason for fitting an intercooler. One other reason to fit an intercooler is to reduce the overall temperature of the engine - I fitted an intercooler (well two in series due to space limitations) to a turbo diesel engine and it reduced the running temperatures by about 8 to 10 degrees C measured at the coolant temperature which was very handy 98 deg C to 88 deg C made a huge difference to the running and reliability.

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tl;dr: Yes. In general, a good heat shield can usually beat a relocated intake in performance, price and complexity.

We've discussed the benefits of cool dry air many times before. I'll summarize the cool air side of things by citing the ideal gas law again and reminding you that what you really want are more air molecules per intake gulp. Cool air = more air molecules per unit volume = more potential for combustion.

However, Grassroots Motorsports just published an interesting article on the design of air intakes. The main thrust of their investigation was that, to get away from engine heat, you'd need a fairly significant airflow path to reach from the intake manifold to the new filter location. They set up a test rig and tried some representative piping to see what effects that would have on the net cubic feet per minute (CFM) of air reaching the simulated manifold.

I don't want to spoil their article (it's a good read) but I will say that they were able to cut airflow in half by creating what sounds like a cheap and cheerful front-mount intercooler equivalent. That's going to be a disappointment, no matter how much lower the temperatures are.

They also cite the benefit of a heat shield, which I can second. My favorite intake on my old Integra was a cone filter in the original panel filter location, hidden in a thick plastic box with a snorkel running down the fender. It gave me the benefit of a short intake path, prevented a lot of heat soak and I never had to worry about water ingestion.

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Maybe an aftermarket intercooler in the front bumper grill could give you more cold air flush, increasing bhp and torque.

Anyways if they designed it like that it should be good as it is.

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