Crankcase vacuum question.

[1cheap1]

You are right about mpg in that car. The best i was able to get was 20 mpg. Now its about 15. I only use it once in a while. It is still better than when i had a 69 dodge Super Bee, 4 to 6 mpg. That was in the 1970's.

[suspendedhatch]

Originally Posted by 67 Satellite

If I understand what you're suggesting correctly, this would cause the engine to idle very fast upon start up. All of the air in the crankcase would be pulled into the engine,like a vacuum leak,until the preset vacuum level was reached.Don't know how long it would take for the r.p.m. to "settle down" or how fast it would run until then.

No... sucking crankcase pressure into the intake manifold to be fed back into the engine isn't like a vacuum leak.

67 Satellite beat me to it. There's only "vacuum" at very low throttle angles. To accomplish what you want without an electric or mechanical pump you will have to use a slash cut tube mounted in the exhaust. You could do a slash cut in the intake tube but then again, that's already present in most OEM designs.

[ZugyNA]

Originally Posted by 1cheap1

On my twin turbo 3000gt i run about -19 to -20 vacuum on the boost gauge at idle. Under normal load and no boost its -8 to -10. On our forum for the GT's it is recommended to keep the pcv valve set up. Under hi boost (14 to 19 psi) i do get some oil blow by and i have a ketch can for this purpose. I am using a SSQ Blow off valve by HKS. It can be set up to be external or internal. We keep the pcv set up because if we don't out ECU will not work at its best.

That is manifold vacuum...you need a vac gauge set up to measure vac in the crankcase (PCV system). The restriction needs to be where the air from the filter or breather goes into the crankcase to feed the PCV flow...need NO leaks...flow is not that great. Basically want to see the vac at idle or under cruise conditions max out no higher than maybe 5" hg? Won't see ANY vac under WOT.

[GasSavers_RoadWarrior]

Hmmm just thunk of something else. I have hydraulic lash adjusters in Marvin, pulling a vacuum on the crankcase may mean they bleed down at high vacuum, thus resulting in lower valve lift. That should make for a theoretical economy boost also. However, I'm not sure if that would be very good for the valvetrain when you lift off the throttle sharply at 5000 rpm... unless it took a few seconds to suck them down... then the revs would probably drop fast enough for it to work out okay... though they should also have much more oil pressure keeping them pumped at that point... hmmmm

[67 Satellite]

Originally Posted by suspendedhatch

No... sucking crankcase pressure into the intake manifold to be fed back into the engine isn't like a vacuum leak.

67 Satellite beat me to it. There's only "vacuum" at very low throttle angles. To accomplish what you want without an electric or mechanical pump you will have to use a slash cut tube mounted in the exhaust. You could do a slash cut in the intake tube but then again, that's already present in most OEM designs.

Without a p.c.v. valve in the hose it will be a big leak. The valve has a weight and spring arrangement inside to restrict the flow and provide resistance to the manifold vacuum.This is why my crankcase vacuum at idle was only 6" Hg while the manifold vacuum at idle is 19"Hg. Without the restriction of the p.c.v. valve the entire volume of crankcase air must be consumed through an open hose to get any vacuum in the crankcase at all.This air will be seen by the engine as "throttle opening" and it's speed will rise.The engine doesn't care where it gets it's air.

[ZugyNA]

Originally Posted by RoadWarrior

Hmmm just thunk of something else. I have hydraulic lash adjusters in Marvin, pulling a vacuum on the crankcase may mean they bleed down at high vacuum, thus resulting in lower valve lift. That should make for a theoretical economy boost also. However, I'm not sure if that would be very good for the valvetrain when you lift off the throttle sharply at 5000 rpm... unless it took a few seconds to suck them down... then the revs would probably drop fast enough for it to work out okay... though they should also have much more oil pressure keeping them pumped at that point... hmmmm

Not sure what the " hg equivalent for PSI is but I doubt that oil pressure would be affected much by just 5" hg in the crankcase? Might be a little more oil come out of the bearings and lifters...probably not enough to matter? Main thing would be to keep tabs on the vacuum...don't let it get too high?

[R.I.D.E.]

Barometric pressure runs 26-31 inches of mercury.

Atmospheric pressure is about 14.7 pounds per sqaure inch.

A good rough ratio is about 2 to 1, IE 10 inches HG equals about 5 inches of vacuum.

regards
gary

[GasSavers_RoadWarrior]

Originally Posted by 67 Satellite

Without a p.c.v. valve in the hose it will be a big leak. The valve has a weight and spring arrangement inside to restrict the flow and provide resistance to the manifold vacuum.This is why my crankcase vacuum at idle was only 6" Hg while the manifold vacuum at idle is 19"Hg. Without the restriction of the p.c.v. valve the entire volume of crankcase air must be consumed through an open hose to get any vacuum in the crankcase at all.This air will be seen by the engine as "throttle opening" and it's speed will rise.The engine doesn't care where it gets it's air.

Just thinking actually that I read somewhere that that opel mileage car worked just like that, pulled all it's air through the crankcase.

[rgathright]

I am very curious about this as well. Please post more detail, IE: the model of the pump used and any equipment.

I will then test it on my Dakota this summer as well.

[67 Satellite]

Assuming you have a wet sump oil system,the oil pressure won't be effected at all. The inlet side of the oil pump is in the same vacuum as the outlet side,it will just pump oil from point A to boint B.If it were pumping oil to the outside of the engine then it would have to fight the vacuum,but within the engine the pressures(or vacuums) on both ends of the flow path are equal.