944 S2 - Drilling airbox?

[zcacogp]

Chaps,

After reading this page here:

http://968engineering.com/pdfs/airbox

I thought I'd have a go with my 944 S2. Examination of the airbox revealed that the engine breathes through a comparatively small duct in the corner of the airbox. So, to cut a long story short, I removed the duct (fiddly job), and drilled four large (4cm diamater) holes in the front of the airbox. This exposes a large amount more of the filter (previously it really did look like only about half the filter was used, and this was bourne out by the fact that one half of it was much cleaner than the other half) and should allow a significantly greater airflow through the system.

I haven't driven it much afterwards, to be able to assess the difference, but it seems that it makes it a little more responsive in the mid-range, and has taken some of the sharpness out of the familiar 'step' in performance at around 4,000rpm. It has changed the noise of the car on full chat - it is slightly louder (not as much as I'd expected) and sounds a little 'flatter' (less interesting, unfortunately.)

More detailed testing is obviously needed (without the passenger-seat speed limiting device aka. The Wife installed). But I was wondering whether anyone else has ever done this and what their experiences are? (I did it on all my Golf's, which had a similar airbox arrangement, with good results every time.)

Thoughts?

Probably should add - this is with an otherwise stock '89 944 S2 - no chip, standard paper air filter.


Oli.

P.S. Apologies for the cross-posting.

[968csreading]

A few of us 968 owners have done it and there has been much descussion on the 968 forum

www.porsche968uk.co.uk/phpbb/viewtopic.php?t=2249

I have done it on mine (four large holes) and although I can not feel any difference in performance induction noise has increased and there has not been any negative effects.

[zcacogp]

968CS - thanks. Interesting.

Looks like the jury is out on whether it does any good or not, but there is nothing to lose.


Oli.

[apusmelba]

i think porsche designed and tested the airbox to do the optimum job
the filter will collect particles from the venturi end first but the design
intent was the filter was long enough to last the recommended service interval
drilling holes in the front cover may or may not have a negligible effect on
performance and individuals perceptions are not a good guide to comparisons but i would
not be happy to have sections of a paper filter being directly exposed to airflow in a straight line
from a foreign object impact ie a sub 40mm dia solid penetrating a paper
filter
so if you want to drill holes why not use the top/bottom of the cover?
and why not take the cover off and see if it makes a difference
or why not fit a cleanable filter across the whole air inlet behind the towhook socket?

[zcacogp]

apusmelba said:

i think porsche designed and tested the airbox to do the optimum job
the filter will collect particles from the venturi end first but the design
intent was the filter was long enough to last the recommended service interval
drilling holes in the front cover may or may not have a negligible effect on
performance and individuals perceptions are not a good guide to comparisons but i would
not be happy to have sections of a paper filter being directly exposed to airflow in a straight line
from a foreign object impact ie a sub 40mm dia solid penetrating a paper
filter
so if you want to drill holes why not use the top/bottom of the cover?
and why not take the cover off and see if it makes a difference
or why not fit a cleanable filter across the whole air inlet behind the towhook socket?

Hmm, good points, thanks. Particularly the one about the possible impact from foreign bodies.


Oli.

[968csreading]

On the 968 the holes are drilled below the filter so I can see you point. However, in the US they have not experienced and problems with dirt, dust or water entering the box.

If you could pick a spare box up on the cheap carry out the mod and if you are not happy with it you could replace it.

[nervous]

ami right in saying that the airbox on the 944 is the same size as the one on a '91 audi 80? if so, i may be able to help your little experiment.

[hoges senior]

This was done to my 964 ('project 964' from 911 & Porsche World magazine) Not sure it has any effect on performance, but it does sound the bo*$+*ks when you open her up

Link to the article below:
www.porsche964.co.uk/rev_rep/rreports/images/praby/safeandsoundscr.pdf

[968csreading]

Just checked my air box t0 clean the filter (which wasnt dirty anyway) and the drilled holes are under the filter so any debris will be picked up by the filter.