Bill Verburg

I've had a lot of headaches wrt the vacuum system used on 993VRAM, You can easily loose 50hp if it's not functioning but it doesn't usually just stop working but rather a gradual decline in performance that is unnoticeable day to day. Maybe someone else has too, so I had some time today and started putting together some info on it. It is complicated w/ 5 different solenoids scattered around the car(can you find them?) and many connections each of which is susceptible to a leak

993 vacuum systems

race911

Makes you appreciate the "simplicity" of carbs sometimes!

Glad I've not had to poke around the system too much (absent one nightmare supercharger-back-to-stock deal I got tied up with about 10 years ago), but I'll thank you now for a chart I'll inevitably need to refer to in the future.

KMASS993

Bill - I have become very intimate with the system from an assembly perspective. I spent months messing around with my system when one of the intake runner seals came loose and lodged itself sideways in the runner. It's pretty archaic how the system is put together with the plastic tubes and rubber fittings. You would think that would have designed a much better connection mechanism. I have a spare intake manifold and have kept all the vacuum parts in case mine fail, but tested all of them while they were out. Thanks for the information, will def be reading in case I did anything wrong! Thanks for posting!

Garth S

In seeking failure modes of the VRAM, it is perhaps worthwhile repeating that a covert degration of the VRAM occurs as the interior of 'branch piece' #10 delaminates and restricts vacuum: this is the connector on the center branch of the 'tree' from the vac reservoir .... insurance against failure is to install a stent in the throat of this item: mine is an ~20mm lenght of a colt 45 recoil spring.

Mike J

What is the source and solution of the oil pooling issue I have seen on several vram manifolds? (crankcase venting?) It's seems to pool at the lower resonance flap controller, and often is also at the base of the intake runners...

Cheers,

Mike

ToSi

The check valves seem to fail intermittently, eventually leak completely & the diaphragms in the actuators tear.

Use one of these to check the individual components:

EckFe1

My mechanic told me to make sure that my oil level isn't too high, otherwise the mainfold will eventually accumulate oil and since the lower flapper valve is at the lowest point of the manifold, all the oil drains then at that location.
Ed

Bill Verburg

that's been my experience too, the combination of revs and high oil levels causes a lot of oil to be ingested into the intake manifold.

I never fill above 50% and try to keep it lower than that

JPP

^^^ So .. in hind sight, would it have been better for you (Bill) to have stayed with the '95 pre-varioram system on your 3.8 build or would it have even worked? If this is a stupid question I apologize in advance ...

Bill Verburg

For my purposes the plastic non vram manifold would be preferred, for street use the vram would be preferred.

At the time I wanted a fresh engine in my track car and the 102mm high compression pistons and the RS cams/valves.

Eventually I'll rebuild the non vram motor for track use, 3.8-4.0L race cams/valvetrain, race rods etc It's already got the correct cosmetics.





That motor will then go back into the 993 and the vram will go back to the C3

JPP

^^^ yes, that makes sense, and I would agree after owning both systems on street cars, the vram for street driving is really good. It just struck me that losing 50h.p. randomly over time in so many possible places in the vram system that having the stability/consistency and trouble free performance of the simpler system would trump any horsepower gains of a functioning vram system.

Bill Verburg

My car is quick enough that when down 50, you know there is something lacking but it's not enough to panic over because it's still keeping up.