Thread: Air Filter Tests - Teaser

Originally Posted by Red90

Ummm Ben.....

A TDI runs at 1 bar boost..... That is 200% of the flow times the pumping efficency of the engine......

Thanks Red. I don 't know how I managed that one... I knew it was about 16psi, but I mist have stuffed up when I converted to atmospheric pressure...

Funny thing is - I have known that 14.7psi = 1 atm for years... I blame brain fade from all the assignments and theses I have to mark at the moment.

Originally Posted by Red90

Ummm Ben.....

A TDI runs at 1 bar boost..... That is 200% of the flow times the pumping efficency of the engine......

That's twice the air with perfect intercooling, with no intercooler you're about 160%. Pick somewhere in between 1.6 and 2 depending on how good your intercooler is.

Originally Posted by isuzurover

For a 300Tdi that is 1800rpm. For a 3.9V8 that is 2500-3000rpm. If the V8 has 100% volumetric efficiency, and the TDI has 116% VE (boost is approx 16% of an atmosphere) - then my back of the envelope calcs say that the Tdi will be flowing about 45 lps, and the V8 85 lps (at 2500rpm). Even if you drop the revs to 1800, the V8 will still be flowing 60lps (at 100% VE).

From what I understand it is unlikely that you would get 100% VE even under ideal (standard) conditions.

When looking into the size of a donaldson air filter to use, they have this simple calculation for air flow:
CFM=engine H.P. x 2.5
as a rough guide.

A more accurate calculation for air flow is:

For normally-aspirated engines:
CID x RPM / 3456 x 0.85 = CFM required
where, CID is engine size, in cubic inches (CID= ccx0.06102),
RPM is maximum engine speed,
0.85 is a close approximation of VE

For turbo or supercharged engines:
CID x RPM / 3456 X % boost + 1.00 = CFM required
N.B. As normal inlet air pressure os 14.7 PSI, a boost of 6 PSI gives 20.7PSI, or 140% boost

Hope this is of some use to someone

Very interesting too. I've got a K&N so would be interested in the results too.

Wonder if the snorkel will make much difference to the airflow and particulates being drawn in?

I'm resurrecting this thread for two reasons:

. firstly I'm wondering if isuzurover has finished his testing

. secondly, some of the threads seem to suggest that the size of the tdi filter is overkill for the size of the motor. If this is the case, why do some people consider a 75 mil snorkel to be inadequate to provide air...has this actually been tested or is it just perception?

Thanks for reminding me to pull my finger out and finish analysing the data...

Watch this space...

I finally got the data analysed...

See this thread here: Air Filter Tests (Finally)

I started a new thread as I noticed comments in some of the other forums tyhat the test "didn't seem very scientific"

Originally Posted by JDNSW

Just a comment - the assumption that a 3.9 V8 would have a higher airflow than a 2.5 Tdi is not necessarily correct (it may be, but not necessarily).

For a start, if we assume that they have the same maximum rpm, just to simplify things, and at full power there is no throttle restriction on the petrol engine, then the amount of air taken in by each engine will be proportional to the swept volume, everything else being equal. But it is not equal - for a start, around 8% of the volume going into the V8 cylinders came out of the injectors, and is the flow restriction of the valves the same? (I don't know the answer!). But the BIG difference, is the turbocharger, which is pushing air into the diesel at a higher pressure. Again, I don't know the answer, but I strongly suspect the diesel, after taking this into account, is pushing more air in at full power than is the V8.

And in any case, diesels are unthrottled at all times, so unless you drive the V8 wide open all the time, the amount of air going into the diesel will easily exceed that going into the V8 on an average per kilometre basis. So perhaps the engineers did know what they were talking thinking. Of course the air cleaner size was probably really determined by how much room was left in the engine bay!

I look forward with considerable interest to the filtration results.
John

John, I do know that a modern well tuned naturally aspirated petrol engine has about 75% Volumetric Effiiency (VE), any motor of similar size that was Turbo'd or Supercharged would definitely have a higher VE. So at 1 Bar. that would mean 100% VE, wouldn't it?, Regards Frank.