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Hoooking a vacuum pump to a crankcase?

Hoooking a vacuum pump to a crankcase?

Hoooking a vacuum pump to a crankcase?

(OP)
I have seen the setups where you hook a line to a mount on your header and crankcase to create a vacuum.  I have also seen a electric vacuum pump made for a brake booster that says it creates a max of 20hg of vacuum.

Can/will this make a noticable hp increase when hooked to a crankcase or valve cover?  Differences between the 2 locations?
Replies continue below

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RE: Hoooking a vacuum pump to a crankcase?

i would think that you would have to run lower tension rings to achieve the hp increase.

RE: Hoooking a vacuum pump to a crankcase?

Well, the vac pump would need to flow somewhat more than the rings will leak past.
If you pull much of a vacuum, you will then need an oil sump that can handle the pressure differential.
How many pounds/square inch will it take to reduce windage losses? Compute that many psi times all the square inches of the sump...(what was that crushing sound?)

The vac pump will almost certainly cost more power to drive than you would gain from the reduced windage.

Jay

Jay Maechtlen

RE: Hoooking a vacuum pump to a crankcase?

You also need to have oil seals that will seal in both directions to stop oil getting out and air getting in.

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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RE: Hoooking a vacuum pump to a crankcase?

hmmm... I thought that evacuated crankcases were already used in some applications?

RE: Hoooking a vacuum pump to a crankcase?

They are, and have been for as long as I can remember.

Anything with a dry sump and a half decent scavenge pump reduces pressure in the crankcase. It all depends on how low you want to go.

To go real low without to big a pump, you need a good seal to stop air leaking in.

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Hoooking a vacuum pump to a crankcase?

You usually use adjustable air bleeds mounted in the valve cover to control the level of vacuum. Most drag engines have used them successfully for years with very narrow/light ring packs.
Tim

RE: Hoooking a vacuum pump to a crankcase?

Around 1976 Bill Jenkins was claiming better oil control, thus reduced oil getting into the combustion chamber. I think he mentioned even tiny traces of oil causing detonation.

RE: Hoooking a vacuum pump to a crankcase?

To much vacuum, you lower the boiling point of your oil to the point it becomes an issue, and you suck contamination past the seals into the crankcase, and maybe even crush the sump and tappet covers if they are thin pressed metal.

Just enough, you boil of fuel dilution from the oil, and reduce or eliminate oil past the rings and the guides. Some claim you also get a windage advantage.

Detonation from oil contamination of the chamber only occurs if you are already very close to detonation, but of course this is often the case with very serious race engines.

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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