I'm not entirely sure what you're asking... Which year and model focus are you running? Any mods?

If you're asking about the air intake, then yeah, having one that's open on some cars will result in hotter air entering the car. The MK3 ST, for example, performs better with a closed intake and a ram air intake than it does with an open airbox, at least with stock turbo.

 

Thank you. My question was regarding the hotter air entering the system - would it if it has to pass through an intercooler? I have a 1.6 ecoboost.

I hope I’m not making myself appear daft, it’s just a question that I’ve always wanted to ask.

 

My ecoboost is remapped and I have the k&n 57s 4000 - so have a bung on the end of the filter that I can have on or off.

 

In general, on a turbo'd car, having an open airbox results in higher air temps, as you're letting the heat in the engine bay more directly affect the air going into your air intake. The reason it matters whether or not you're turbo'd is just because turbocharged cars tend to run warmer than NA cars.

If you have a good intercooler, the effects can be somewhat negated, but an intercooler only cools air that is pulled through the turbo, meaning your air coming through your intake and not running to the turbo is unaffected by the intercooler. So at the end of the day, you're still getting some hotter air into your engine, which results in worse performance.

I'm oversimplifying a lot here to make the explanation simple, but that's the general rule of thumb. It can vary greatly car to car, depending on engine position in relation to the air intake, how effective your cars cooling systems are, how good your intercooler is and even what the weather outside is like. Muggy hot days will result in worse air.

 

If you have a good intercooler, the effects can be somewhat negated, but an intercooler only cools air that is pulled through the turbo, meaning your air coming through your intake and not running to the turbo is unaffected by the intercooler. So at the end of the day, you're still getting some hotter air into your engine, which results in worse performance.

All air going into the engine is going through the turbo and intercooler, sometimes more than once due to BPV/CBV plumbing.


Regarding your question Chris, air to air intercoolers aren't 100% efficient, and won't cool air back to ambient temp. So, the cooler the air going into the turbo, the cooler the air exiting the turbo is, and the closer to ambient the intercooler will be able to cool. While the impact may not be as great on a turbo car (since the turbo is the biggest contributor to heat) cooler IATs are still important.

When looking at the ST250 and Mk3 RS specifically, Ford uses a torque target calibration instead of boost. So, the ECU is targeting specific torque values instead of boost, so it can increase boost to achieve the same targets. This also results in higher/lower IATs having less of an impact on overall power. But, there are limits to how much boost can be added, so it doesn't mean it can counteract sky-high IATs. Since your car is mapped, it's likely boost targeting now, so to get the most power, you want the coolest air possible entering the engine.

If you have the ability to datalog, look at pre-turbo IATs and charge air temps (manifold or post-intercooler). Do the same with the filter plug in or removed. See what the difference is, if any, and remember to compare against ambient air temp.

 

Thank you so much for your explanation. I’ll put the bung back on. All the best