how much vacuum?

**laaag** · 03-01-2006, 12:40 AM

i was just wondering how much vacuum a naturally aspirated 4age would produce in psi?
i have searched to no avail

any help would be appreciated
cheers

**myne** · 03-01-2006, 12:45 AM

My 4agze idles on about 20 "inches of mercury" which I believe is more or less a linear opposite of PSI.
4AGE's should be roughly the same.

**takai** · 03-01-2006, 12:47 AM

Yeah, most 16vs produce between 16 and 20in/Hg

**brett_celicacoupe** · 03-01-2006, 12:48 AM

im wrong......

**oldcorollas** · 03-01-2006, 06:13 PM

Originally Posted by laaag

i was just wondering how much vacuum a naturally aspirated 4age would produce in psi?
i have searched to no avail

any help would be appreciated
cheers

well... i think in terms of kpa, engines typically idle with around 20-60kpa....(depending on cams, milder cam = more) and 101kpa = 14.7psi

soooo.... say an average of 50kpa vacuum = about 7-7.5psi vac??

**SeptemberSquall** · 03-01-2006, 06:58 PM

but there is no such thing as pounds per square inch in vacuum, because pounds per square inch is a ratio of pressure..?

**laaag** · 03-01-2006, 07:13 PM

Originally Posted by SeptemberSquall

but there is no such thing as pounds per square inch in vacuum, because pounds per square inch is a ratio of pressure..?

hmmm my bad.
the reason i asked is because i have seen boost/vac and only vac guages measured in psi... at least i think?

**RobertoX** · 03-01-2006, 07:24 PM

Pounds per square inch is a measure of pressure and the 'vacuum' being talked about can still be seen a positive pressure in absolute terms.
Say you are measuring at 1 atmosphere which is 14.7 psi (like oldcorollas said) and you are reading 7psi vacuum then the actual pressure seen is 7.7psi.
Both the pressure readings are just relative to some reference pressure and the vacuum read from an engine should not be affected by whatever the reference pressure is (too much anyway, with normal atmospheric variations). I think it is still valid and useful, it just depends on what scale you are used to using.

**oldcorollas** · 05-01-2006, 12:47 AM

sorry i should have made that clear....

i always work in absolute pressure terms, but tried to make it more understandable by giving it as a psi rating of vacuum....

but 7psi vacuum just means 7psi less than normal pressure..... well.. thats what i meant..