Air Filters
11-03-2013, 03:00 PM
#1
Banned
Thread Starter
Air Filters
I was thinking of replacing the stock paper filter with two 3.25 flange inlet 7 inch long K&N type conical filters mounted at the end of the filter box instead of the inlet hoses. My hoses are pretty much shot and need replaced.
One could gut the paper filter and retain the rubber gasket so the top and bottom of the air filter box would mate correctly.
Since the inlet hoses mount over air ports on the timing belt cover, do these ports require a small filter or what is their purpose?
I am replacing the stock engine driven fan and aux electric fan with a single electric unit and would have to modify the top fan shroud to continue to use the inlet hoses.
Any suggestions?
One could gut the paper filter and retain the rubber gasket so the top and bottom of the air filter box would mate correctly.
Since the inlet hoses mount over air ports on the timing belt cover, do these ports require a small filter or what is their purpose?
I am replacing the stock engine driven fan and aux electric fan with a single electric unit and would have to modify the top fan shroud to continue to use the inlet hoses.
Any suggestions?
11-03-2013, 03:17 PM
#3
Nordschleife Master
The stock set-up is actually really good. The filter is very big and does not restrict flow.
I tried to improve the system by making an open-topped frame to hold the filter in place. That allows hot air into the intake and resulted in a 5hp loss on the dyno!
Look at the area of the filter and then the area of what you want to put in. More area is better. Getting cool air from in front of the radiator is really good for power. A cooler charge is a denser charge.
I tried to improve the system by making an open-topped frame to hold the filter in place. That allows hot air into the intake and resulted in a 5hp loss on the dyno!
Look at the area of the filter and then the area of what you want to put in. More area is better. Getting cool air from in front of the radiator is really good for power. A cooler charge is a denser charge.
11-03-2013, 08:15 PM
#5
Chronic Tool Dropper
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FROM the timing belt covers. Just enough flow to keep things inside from getting stuffy I think. The intake air passing along the tops of those little nozzles draws the air from inside the covers. Mark Venturi theory of diifferential pressure... Not sure why it's called that, since it's about as far away from the differential as you can get on a 928. [scratches head...]
11-03-2013, 08:41 PM
#6
Inventor
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11-03-2013, 11:12 PM
#8
Rennlist Member
Hmmm. Mine are disconnected due to the supercharger hoses going over there. wonder what affect that will have on things?
11-03-2013, 11:47 PM
#9
Team Owner
the cool thing with the timing belt vents is that if there is a belt tracking issue it can be seen in the air filter,
as belt chips will be caught by the air cleaner,
and when its tapped out on a white surface the belt rubber bits will be evident.
The idea with the belt vents is to vent the front of the engine,
and any other vapors from the engine will be drawn back into the engine
as belt chips will be caught by the air cleaner,
and when its tapped out on a white surface the belt rubber bits will be evident.
The idea with the belt vents is to vent the front of the engine,
and any other vapors from the engine will be drawn back into the engine
11-04-2013, 12:14 AM
#10
Three Wheelin'
Really ingenious yet simple in design... although i tend to think they were put there as an inspection hole for the timing belt more so. But what's been shown above makes sense. I think the intake system on 928's is fine the way it is, these aren't run of the mill Hondas or Fords. Stock air filter has a lot of surface area, which matters above all, next to the main intake diameter before the throttle body. I think the stock intake can support more than enough air without causing restriction than the CFM requirements of a stock 928 V8. One thing that i want to know is why they started putting insulation over the GTS intake pipes, i think it was more for the intake air sound than anything. I was running without the pipes for a while for some reason or another and noticed quite a bit of air intake noise, just a constant "air flowing" sound, lol.
11-04-2013, 12:28 AM
#11
Nordschleife Master
Air goes in, air goes out. I suspect it'll go in both directions depending on operating conditions. Do people have test or document references? I was good at fluid mechanics back in school (in another century) and could see the pressure differential going either way.
Straight pipes with insulation will have the best flow, be quiet and reduce charge temp rise. People have analyzed all this and the last bit it the least affected; the air is moving too fast to pick up much heat. More flow while being quiet seems the reason for the insulated GTS tubes.
I believe it was Louis Ott who said that the venturi tubes had no negative effect until the airflow rate reached a point that supported 350 horsepower. I've replaced the tubes on my current track car with 3" brake duct as it's getting near that point. And why not? A bit more rasp from the engine can be a good thing.
Straight pipes with insulation will have the best flow, be quiet and reduce charge temp rise. People have analyzed all this and the last bit it the least affected; the air is moving too fast to pick up much heat. More flow while being quiet seems the reason for the insulated GTS tubes.
I believe it was Louis Ott who said that the venturi tubes had no negative effect until the airflow rate reached a point that supported 350 horsepower. I've replaced the tubes on my current track car with 3" brake duct as it's getting near that point. And why not? A bit more rasp from the engine can be a good thing.