Vacuum in an Intake manifold

[Cart]

I was wondering if someone could explain to me how putting a vacuum in an intake manifold helps air flow into the cylinders?

[anotheridiot]

the intake is the source of the vacuum, all I know is putting vacuum ports in the individual runners balances the vacuum to each cylinder to equalize the cylinders.

[Barry Donovan]

vacuum is a secret. we are not allowed to know it.





I like vacuum because it is a shredder, the longest lasting engines. The low pressure expander makes a super fuel as well. The tease of the low pressure keeps the flow.

the other end of vacuum, the exhaust...
scavenging. two banks of cylinders notice if its sloppy. one bank tugs at another one...only it is on a pressure side after the fire.

big engines tend to ignore that stuff, overlap of 90 degree fires can delay into giant rpm ranges. A 4 cyl or less is a real lesson if you are studying this stuff.

[BigBlockMopar]

You don't PUT vacuum into an intake manifold like you put fuel into it. Where else do you think vacuum comes from?
Vacuum is created by pistons moving down the cylinders when the intake valves are open.

[JeffMcKC]

Air flows to the low pressure from high, when the intake valve opens as the piston is going down, the higher pressure in the intake is forced into the cylinder. All motors are pressurized just some are atmospheric Pressure. This is of of the reasons cam timing is so critical. if the pressure differential is done right, the momentum of the fill will pack more air in the cylinder than It should hold, giving you a higher than 100% VE

[sr440]

Im just impressed that you can spell vacuum!

[Ron Ward]

I'm not sure how the mechanicals work, but I have heard that the best idle quality can be achieved with 18" of vacuum in the intake. My guess is it would take a really, really, tall intake to achieve this.




Ron

[RAMM]

Vacuum doesn't exist, It is important to get used to pressure differential. J.Rob

[Huskinhano]

Air flows to the low pressure from high, when the intake valve opens as the piston is going down, the higher pressure in the intake is forced into the cylinder. All motors are pressurized just some are atmospheric Pressure. This is of of the reasons cam timing is so critical. if the pressure differential is done right, the momentum of the fill will pack more air in the cylinder than It should hold, giving you a higher than 100% VE

Ah, a man who knows his stuff! I also hate the term "back pressure".

[BKBridges]

I'm not sure how the mechanicals work, but I have heard that the best idle quality can be achieved with 18" of vacuum in the intake. My guess is it would take a really, really, tall intake to achieve this.

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Ron

18" of vacuum would be great! I could only fit 10" under the hood and my idle is pretty rough. Thinking about a six pack scoop to get more vacuum in.

[JeffMcKC]

I will add to this, that checking the intake vac is important, to see if you really need the bigger carb, if its under 1 inch of vac at WOT as it goes down the track its big enough already, if it goes over 1 inch the carb has become a restriction. Or something above the throttle plates such as a air cleaner, hood is to close blah blah blah