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Thread: Crank Case Vacumm

  1. #1
    Senior Member MASTER BUILDER
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    Crank Case Vacumm

    Do I need to care what the vacumm is in the crankcase on a bbc race engine? Just curious.

  2. #2
    Are you running a vacuum pump? If yes pulling vacuum will depend on how well the engine is sealed up. Rings and gaskets. If not just make sure the crankcase can breath upward. Valve cover or valley plate.

  3. #3
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Of more concern is, does the crankcase go positive? Pressure pushes out gaskets, then oil and nothing good comes from that.

    Remember also the pistons move as much air below them, if it is there, as they do above them. Parasitic loss is not your friend.

    Curtis

  4. #4
    Senior Member RACING JUNKIE
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    20 inches of Vacuum is worth somewhere between 35 to 80 Hp depending on the engine and the oiling system.

    But you need to seal it up pretty good . .

    We're using an Aviad dry sump system and a Vacuum pump . . Seems to be the hot tip . .

  5. #5
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    The way the prior owner of this car got his crankcase vacuum was putting a bung in the valvecover and plumbing to the vacuumm gauge. Is this a good way to get the vac reading. There is no vac pump on this engine and its a normal oiling system.

  6. #6
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    What's he using to create or pump Vacuum? A "Vac-u-Pan system, installed right will pull maybe 4-5 inches on a good day, if he's got his cylinders sealed really good (Good rings, seated, etc) and all his gaskets are working . . If that's all he's using, a really good oil pan is necessary to keep crankshaft windage at a minimum . .

    But that's all old technology and if he wants to make the next step, a vacuum pump is pretty necessary . . With a good pump you can pull 7-14 inches and that will work pretty good . . But you still need a good oil pan/scraper to keep the windage down . .

    The Engineers claim (and I believe them) that windage in an Engine will require (or use) 35 to 125 HP of parasitic loss. Deeper oil pans with efficient scrapers and directed oil returns lessen the drag of windage around the crank, and you get HP in return. They don't "Make" HP, they just "Free" it up . .

    We finally went to the Dry Sump for several reasons . . one, it eliminates 95% of the windage in the engine. Two, it bulletproofs the Oiling system. Three, if, for some reason, you window the block/pan, the diaper doesn't have the large amount of oil to keep off the race track in front of your rear tires that an 8 qt sump would . . And four, it makes a lot of people who race with us look in the engine compartment and say; "WTF?"

    Granted, it's kind of 'spensive, but what's your head worth? (Old Crash Helmet question)

  7. #7
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Quote Originally Posted by jreiley
    The way the prior owner of this car got his crankcase vacuum was putting a bung in the valvecover and plumbing to the vacuumm gauge. Is this a good way to get the vac reading. There is no vac pump on this engine and its a normal oiling system.
    Yes, that is a good way to get a reading. Pan evac systems may be old school, but not everyone can afford to put a vacuum pump on. There is nothing wrong with doing it that way and if it has 4-5" of vacuum that is much better than positive pressure. Are you running gas, E-85 or alcohol? Gas is much more forgiving of a pan evac system. The expansion of the water in E-85 and Methanol can create a positive pressure in a crankcase if it doesn't have some relief, I.E. vacuum pump, pan evac or just the blowdown tubes you see on blown cars.

    Curtis

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    Its sounds that if I want to optimize the engine hp, I should go to a dry sump oil system. Having said that the cost is high but so is the return.. The next question is whose to use? If that just becomes too expensive, would a vac pump do any good? This is on a gas engine.

  9. #9
    Senior Member RACING JUNKIE
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    Quote Originally Posted by jreiley
    Its sounds that if I want to optimize the engine hp, I should go to a dry sump oil system. Having said that the cost is high but so is the return.. The next question is whose to use? If that just becomes too expensive, would a vac pump do any good? This is on a gas engine.
    There's a bunch of 'em out there . . I'm only familiar with three, but I'm sure most of them are quality systems . .

    Years back we had an Armstrong on the Alky Dragster, then a few years ago we had a Peterson on both the Super Comp car and then the Blown alky altered . . now, the Camaro S/Pro car has an Aviaid and it's a jewel . .

    The three mentioned all will cost somewhere in the area of $2400-$3000 depending on the number of stages, the finish and how much hardware you get with it . .

    But . . with a good pump, you can pull 18-22 inches of vacuum and pick up 80 to 125 HP . . as well as pretty much bullet proof your oiling system . . Think about that . . what does a complete set of Dart 355's cost? And how much HP do you expect out of those heads?

    Just an old guy ramblin' . . .

  10. #10
    Senior Member RACING JUNKIE TheYellaBrick's Avatar
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    A coupla years back we had this discussion on Vac pumps. Any new and recommended units out there ?

    80 -125hp gain would be worth the investment ! But then I'd find more weak links and need to spend MORE money ! :shock: :shock:
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