GUMBALL

What is the purpose of the intake tubes being connected to the cam belt housings ??
How critical is it that they be connected ??

Jerry Feather

With all of the gears, sprokets, bearings and pulleys spinning around under the front engine cover it is like a super charger. The openings are to direct that air pressure to the induction system.

Speedtoys

Huh?

Rob Edwards

I thought it was to create a venturi effect so that local production of ozone around the timing belt is vented up and out of the TB covers, to prolong the life of the belt. Or perhaps just cooling air, for the same intent.

993turbo

This area is not sealed like a distributor. (Where the Ozone issues were discovered on the twin dizzy 964)

Petza914

Not critical at all IMO. With my intake and supercharger setup, mine are belt inspection ports.

928NOOBIE

They are needed to keep the area cool by pulling air from the bottom of the timing belt cover(s). IMHO they are most certainly needed; why would they be there otherwise.

SeanR

I love this place.

Tony

i thought the hole was where you shone the timing light?





cooling and ventilation of the cam belt area. They were designed that way for a reason...don't see why yours wouldn't be connected if you have the stock tubes as there is a hole in them for the cover to begin with.

PorKen

Duh!

Speedtoys

Is it ok to ask for the results of your study on why they are not required?

Wisconsin Joe

My understanding is that the partial vacuum in the tubes pulls air through the TB system. Cooling? Removing 'bad air'? Something else?

No clue.

However, the early 944 had a similar setup, with a tube going from the air cleaner housing to the TB cover.
Later 944s didn't have it.

I would guess that it's not super critical. Lots of super charged cars go without it, and they don't seem to have issues.

But I always make sure my tubes go back over the 'timing belt inspection holes'. And I put the tube back on my 944, even though the WSM says it's ok to delete it and plug the hole in the air filter housing.

GregBBRD

The plastic cover that fits around the rotor and is held down by the cap on a 944 keeps the ozone out of the belt area....

Petza914

My study was very scientific. Drive car around before supercharger installation with stock intake and air tubes installed.

Install supercharger setup leaving ports open. Drive car this way for 4 years and note any negative effects on cam gears or belt wear. Nothing noted.

Seems to me there's enough turbulence inside those covers that heat, ozone, or whatever can escape through the open holes even without a vacuum draw from the intake tubes. I think Porken has the right idea that they're for checking timing without having to remove anything except the intake tubes. Maybe Porsche made them collared ports so coolant or oil leaks couldn't then get through the holes and onto the belts?

Thom

What is the max amount of vacuum ever measured in the intake tubes?