I get slightly different numbers, but not enough to argue about. However, I am not too sure about the 100% volumetric efficiency - certainly every effort is made to get it as good as possible, but the fact that changes such as modifying valve timing can improve power output suggest it is not perfect. But I am quite willing to accept that the % is the same for both engines. My main point is that this analysis only applies if the petrol engine is operating at full throttle. How much of your driving is done at full throttle at any rpm?
I suggest that any realistic driving profile will see the manifold pressure well below atmospheric most of the time. For example, in typical city driving, it will actually be idling for a significant part of the time, with the airflow heavily restricted by the throttle. In contrast, the diesel has no restriction to the throttle at any power setting, although at idling the boost will drop to nearly nothing. This means that the difference in air throughput is nowhere near as large as the displacement based figures suggest.

Another effect will be that differences in flow resistance between different air cleaners will almost certainly be insignificant at any throttle setting except wide open, as the effect of the throttle will be much larger. On the other hand for a diesel, the restriction will have some effect at all times, although it is not clear whether it will have any significant effect except close to full throttle.

John

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JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol

I doubt very much that a 3.9 V8 or any other massed produced 4 cycle N.A. (petrol or diesel) engine will produce anywhere near 100% V.E. at any rev range, a good condition 4 cycle N.A. engine will produce about 75% V.E. on a good day, an extremely modified high performance N.A. 4 cycle engine would be hard pressed to get 100% V.E., Regards Frank.

OK - I stand corrected.
http://www.epi-eng.com/ET-VolEff.htm

However there is some conflicting (erroneous?) info out there:
http://www.autospeed.com/cms/A_2109/article.html


However a 3.9 L petrol V8 at XX% VE (compared to a 2.5 L turbo diesel at XX*1.16% VE) will still be flowing more air.

I agree with the comment about the punched plate versus the open mesh reducing the flow area on the Coopers filter. I do respect Coopers products having used them for many years. An American geek some time ago did a Website featuring an oil filter analysis in which Coopers did very well. I think that Purolator came out top of the oil filter poll. Ryco scored extremely well too but Valvoline, as featured by our friends Super Cheese Auto came out close to a wad of toilet paper in his test. One might assume that filter manufacturers who make good oil filters most likely are OK at air filters as well.

Dunnie, did he actually use a bubble point tester ?
or was it a visual analysis ?
I've only ever seen one independent test using a bubble point tester, and Purolator did indeed do well.
Having specs on some Ryco oil filters, they don't come anywhere near the US stuff in filtration efficiency (beta ratios) although their capacity before going into by-pass is greater (obviously)

Also bear in mind that all manufacturers outsource a lot of their production, including the big boys like Donaldson and Cummins/Fleetguard. They just concentrate on their core lines.
EG, my Donaldson oil filters are manufactured by Champion Laboratories in the US using Donaldson media, as are Fleetguards equivalent filter.

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Are K&N Filters really that bad?
I was under the impression that if they were maintained properly they were really good.
I'd love some constructive feedback.

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Disco
1992 Tdi Manual
ARB Bar, Lightforce 170's
Dual Batteries, Codan HF
GME UHF, Magellan GPS

Defender 130
1995 Tdi Manual

Mucho interesting!
Thanks Ben for sharing!

Hymie - All will be revealed when I have finished analysing the efficiency measurements.

Hymie, in some independent air filter tests it was noted that K&N air filters allowed 38% more dust (particles) into the engine than the standard OEM Paper Filter. I had a K&N air filter in my 03 Ford BA GT, it gave an increase of 6KW at the rear wheels when new, the engine was replaced at 25K because the rings had not bedded in and was using excessive oil, when the plenum was pulled down the amount of dirt and dust in and around the inlet horns was excessive, I have some pics if interested, moral of the story is there is always a trade off for extra performance, but it shouldn't be at the expense of dusting the engine, note: the K&N filter was not responsible for the ring problem, Regards Frank.

Ummm Ben.....

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

Lets say 2.0 * 0.9 = 180%

1.8 * 2.5 liter = equivalent to a 4.5 liter naturally asspirated engine as far as volumetric flow at the air filter. So somewhat higher than a 4 lieter petrol at the same revs. But they rev higher of course.

edit:
To add... To figure out air flow all you need to know is the pumping volume of the cylinders and the ACTUAL pressure during the intake stroke.... Plus or minus, the pressure losses from the air filter to the cylinders will be in the same ball park for these engines. The only difference is that the air is being compressed to get more in with the turbo. 15 psi boost is doubling the pressure.