Engine build differences when using a vacuum pump

[ToddK]

Like the title says, what build differences are used when using a full time vacuum pump, compared to a normally ventilated engine?

[blykins]

Vacuum pumps are generally used in conjunction with lighter tension ring packs. 

[jayb]

Special care has to be taken to seal the crankcase; for example, the area around the distributor, and the dipstick tube, are common sources of crankcase vacuum leaks, even though they may not leak oil during normal operation.  Also usually a double lip seal or a reversed seal, in the rear main and front seal positions, needs to be used.  When running high vacuums on a standard wet sump oiling system the vacuum in the crankcase will cause oil pressure to decrease.  I have also heard that engines running a lot of vacuum tend to starve the wristpins for oil, but I don't really know if that is true or not.  I've usually limited crankcase vacuum to 10-15 inches when running a wet sump oiling system.

Running 10"-15" of vacuum picked up the 510" FE in my Mach 1 from 10.60 to 10.45, with no other changes.  That's probably about 20 HP, a very worthwhile modification.  This was also with a standard tension ring package; I had no thoughts of running a vacuum pump when I built that engine.  Probably more to be gained with a light tension ring pack, in terms of reduced frictional losses while still maintaining a good ring seal with the crankcase vacuum.

[blykins]

I generally run 10-12 inches as well.  I've never seen oil pressure issues with wet sumps with that level of vacuum, but do keep an eye on it during a pull.  If you use a GZ Motorsports setup, the regulator is screwed right into the pump, which makes it super easy to adjust it.  I've also used Peterson setups and mounted a regulator to the valve cover. 

FWIW, I've never done anything special with the timing cover or rear main seal on my FE engines.  Just a normal seal setup and I've still been able to pull over 10 inches of vacuum with no issue.  On my Windsor stuff I'll run teflon seals.  I do put a light coat of white grease around the distributor seal and on the valve cover gaskets. 

Nice bump on the ET Jay....especially for standard tension rings. 

[fe66comet]

I wonder why that technology has not crossed over to street use? Other than a PCV system which kinda helps ring seal. I would guess cost has a lot to do with it.

[ToddK]

Thanks for the replies. So it won't be catastrophic if I run a vacuum pump on an engine not specifically built for it, but it won't work at an optimum level.

[Barry_R]

Pretty much what has been said.  I have seen some reasonable power gains - on the order of Jay's comments.  A lighter ring pack is going to be beneficial, but it'll work with normal stuff - just not as well.  I do see an oil pressure drop but its pretty much meaningless in scale at these levels.  I have run normal FE sealing components and used the four vane Moroso pump with a regulator.  I suspect that the pump would be able to generate much more vacuum if the engine was really sealed up but we were on the regulator pretty quick anyhow and I held to +/-12 with the wet sump so it did not seem to matter.

[ToddK]

Reason I was asking is that I have a Star Machine kit that I planned to use on my race engine. However, we plan to get the engine going and the car sorted without the pump, and so the engine has been put together accordingly. Once I get the car sorted, I'll try fitting the vacuum pump and see what difference it makes. And when the engine gets pulled for a freshen up, we might look into using lower tension rings, etc. Also, the Star Machine pump I have has a built in regulator that is set at 12".

[fe66comet]

Pardon my ignorance on the subject but what happens if higher vacuum is allowed? Why only 12", when I build my Comet I am thinking of running dry sump.