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Evo ix engine vacuum

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I run the auto verdi drysump on my engine, I’m trying to keep the crank case in vacuum as much as possible. I understand eventually at 50 psi of boost I will get positive pressure so I’m running two -12 breathers with one way valves to elevate this.

I also have a vacuum regulator on one port of the rocker as my only concern at high rpm coming off the throttle I may experience too much vacuum and I don’t want the crank seals to flip or pull air in via any seals.

what sort off max vacuum should I be looking to run I’ve done a search to find information on the seals etc but no information is available.

anyone got any experience with this

Hello, i prefer not to pull more than around 8 inches of vacuum in any of the engines I have run a dry sump on, I cant say why it was just something I was told growing up with drag racing and dirt track sprint cars, at that vacuum I never have had any issues with oil seals failing.

My thoughts - more discussion points.

You seem to have been giving this some thought, and the pressure relief breathers is a good idea. For the pump scavenging, you should have the displacement per wafer per rpm of the rotation and so be able to work out the theoretical scavenging volume at your peak rpm. From this you can figure out what vacuum regulation valve, or valves, you'll need for for sufficient air entering the engine - being depressed, the mass is less and so the theoretical regulator valve(s) flow, but it's giving an additional safety margin. This will also mean backing off at peak rpm won't spike the vacuum.

Something many don't consider is that the air pulled in by the scavenge pumps is critical to their efficiency. Part of this is because of the oil droplets and mist physically being carried by the air, but also because the pumps 'pull' the oil by applying a higher vacuum in the lines, than crankcase, to suppliment the gravity feed, and the lower the difference the poorer the scavenging.

As Ross mentioned, seals can be a problem with higher levels. The main problem is that they're designed with the lip orientation to hold fluids in with mild spring tension and internal pressurisation holding it against the 'shafts. Under crankcase vacuum the seals are pulled away from the 'shaft and this can allow air and dirt into the engine - some have fitted the seals backwards or where there's room run two, reversed. There are also specialised seals, such as double lipped designs, made which may be in available in suitable sizes.

Ross's 8 inches is good and, AFAIK, the most usually run is around 15" of mercury on prep'd race engines - some might run a little higher (lower?), but it can be tricky getting it right.

I’ve tried looking for specific seals but no joy with the Evo

The regulator valve is an aeromotive mechanical-12 size valve

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