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850 aftermarket air-filters[ALL/1998] posted by Terence Lui on
Saturday, 25 October 1997, at 2:54 a.m.
Hi,
I am wondering if anybody has put an aftermarket performance air-filter in their 850 apart from the K&N. I currently have the K&N in my 95 854T. It works pretty well. But recently, I came upon the Aerofilter by ROAR. It replaces the stock air-box. They said it will increase 18HP. Does anyone has any opinion on this? I know a lot of people loves these kind of cone-style filters, but I also heard that they might actually make the engine loss power because it absorbs hot air inside the engine bay. Any opinion?
Terence Lui
95 854T
Re: 850 aftermarket air-filters[ALL/1998] posted by Paul Elliott on
Monday, 27 October 1997, at 1:04 p.m.
The advantages you have with the stock air box has a few levels. Your Volvo's airbox is engineered to act as a Helmholz resonator to improve cylinder filling in the low-to-mid rpm range. Its volume, and that of the intake manifold and
associated piping, are of sufficient size as to allow free breathing. The most restrictive portion of the intake system is, therefore, the air filter itself. Which is why a drop in K&N can be helpful. Testing has shown though that the stock filter can more than handle the breathing requirements. I got one anyway!
In addition, the plumming brings the relatively cool outside air into the air box. But of course we have intercoolers to cool the charge. So, perhaps the cones effect of breathing hot air has more deleterious affects to normaly aspirated engines without the bennefit of intercoolers to counteract the effect of hot air breathing. If I remember correctly, the air enters the air cleaner from outside with stock air box, or through the hot engine with a cone, travels to the TC where it gets heated anyway, travels to the INterCooler to cool it back down, travels to the throttlebody, and into the cylinders. So as long as you have an intercooler, I'm not sure how bad the effect of breathing hot underhood air really is.
Re: 850 aftermarket air-filters[ALL/1998] posted by Ira Blumberg on
Monday, 27 October 1997, at 6:48 p.m.
Intercoolers have a finite cooling capacity, so if you send in warmer air, the output from the intercooler will also be warmer than if you started with cooler air. Similarly, the output from the turbo will be warmer if you start with warmer air.
The real issue for a turbo car is that boost pressure does not add power. Added air density adds the potential for more power because there are more oxygen atoms to mix with and combust with more gas. As you increase temperature, you reduce air density (PV=nRT for those who remember high school chemistry). Thus, hot air reduces the power a turbo can provide.
Also, don't forget, turbo waste gates work via pressure, not air density. Thus, if you start with hot air, you get far less dense air out of the turbo at a given pressure and the intercooler can only help a little bit.
Notwithstanding the above, other car groups have tested the effect of drawing in underhood air rather than ducted in outside air. When standing still, the under hood air gets quite hot, as high as 120-130 degrees F. Once you start moving, it cools very quickly to near ambient temperatures (at least on Mitsubishi Eclipses). Thus, the underhood air is not that much of a problem.
One other note, cone type filters tend not to muffle intake noise which is dampened by the whole air box set up. Thus, you may notice whistling and roaring with a cone filter, particularly at full throttle or when you let off the gas after hard acceleration.
Hope this helps,
Ira