mark kibort

ive done a lot of actual pressure testing along the intake tubes, and at all different spots around and up the radiator, as well as behind the firewall feeding my dual intake vents at the base of the windshield. Both the front of the car, above the radiator as inlets, and the rear produce max ram effect, near .2psi at near 120mph. by the way, under WOT conditions at the track, my intake is stone cold for a few seconds in the hot pits.

dprantl

There shouldn't be any "belt dust" unless there is a serious problem in there...

Dan
'91 928GT S/C 475hp/460lb.ft

PorKen

I tried an open filter top on my '85. It was noticeable slower in low speed driving, and noisier. (S3s are quite sensitive to air temp.)

I thought it made a difference on my '81, but it was probably just the noise.



Red line below shows where 'cooling' air is drawn in to ventilate the covers to the air tubes.

Norton928

Mark K, do you have any pictures of you vented air box setup?

mark kibort

I should. If I dont find them quickly, ill take a couple of more

Norton928

Thanks. Looking forward to seeing them

Is rain ever an issue with the venting to the windshield base?

mark kibort

never, and Ive had some races in the rain. however, on a street car, it would be less of a factor, due to the lack of room to really make a big vent there anyway. its pretty well sheltered from the hood covering it.

svp928

PArt of what the vents do is move fresh air through the timing covers and clear out the ozone generated by the dist. caps/rotors firing...when there is an open elec spark, it generates ozone, which will quickly deteriorate any rubber it comes in contact with---like the timing belt...so, don't plug those vents up. Don't really need to be connected to the intake tubes, but it needs them open to get rid of ozone.
I have also seen timing belt rubber in the airbox of cars with failing belts, so it appears that air flows into the tubes from these vents...
The later 911 twin-dist. cars actually had recall to vent the distrubutor base because ozone buildup was breaking the drive belt inside...

My car, back-to-back, actually LOST 6hp with air filter lid removed...
Mark K's system seems to work, if you want to improve inlet temps.

Mike Frye

I've never heard that one before.

The distributors are bolted to the face of the timing covers, where would the ozone build up?

Still hoping to find a reference to where Porsche actually mentions those vents or their purpose...

Mrmerlin

FWIW the holes on the tops of the cam covers and with the intake tubes connected to them will pull air and any other loose particles into the aircleaner.
This is easily verified with a failing belt as you can remove the airfilter and tap it onto a white piece of paper and find small bits of belt in the filter

svp928

Mike the dist cap on the 32v cars is open to the belt area, unlike the early cars with an actual distributor.