I've heard of people saying that at idle the manifold pressure sets between 12-18. I have the greddy boost guage and it doesn't have it in that reading.

How would I convert it from inHg(I think thats what it says) into what would read the other way???

 

http://www.aamerica.com/Mall/content/pressure.htm

 

Which one would I use???

 

bump

 

It probably reads in MMHG. So you input your number in MMHG and it gives you the conversion

 

mmhg in what units??

at idle it reads 500mmhg
mightymouse0x is a buddy of mine...

 

Dude, something isnt right there, cause MMHG is a measure of pressure.

 

ok I'm confused.....

on the boost guage it reads

0
above 0 = bar
below 0 = mmHg

at idle the needle is below 0 so its in mmHg(which reads almost 500mmhg at idle)

and when It gets into boost it goes above 0(in to bar's)

the question is other boost guages read

0
below 0 = INHg
above 0 = Psi

How would I figure out what my boost guage is at idle in inhg not mmhg?

I know the conversion for bars and Psi (1 bar=14.6 psi)
but don't know how to convert mmHginto inHg.

 

bump

 

you have a metric gauge which reads different than the standard system here. Its used in japan and europe. 1 bar = 14.7 psi. .5 bar is obviously half of that. Your vac readings are similar to my blitz guage except that mine reads in CmHg. 40CmHg= about ,14 InHg since you guage is in mm just devide by ten to get you reading in CmHg. i beleuive there was a thread a while back on this. Try doing a search on it. hope this kind of helped -alex

 

Pressure and vacuum are the same thing. Vacuum is just a term used when the measured pressure is below atmospheric.

There's really no logical reason why gauge manufacturers chose to use two different units for boost and vacuum, but most of them do. The stock gauge doesn't, reading from -200mmHg to 400 or 450mmHg. There's also no good reason for Japanese gauge manufacturers to continue to use non-standard metric units like mmHg and kg/cm2. A far more appropriate metric unit for automotive manifold pressure both above and below atmospheric would be kPa (kilopascals). 100kPa = 1bar = 14.2psi.

Converting from mmHg to inHg is no different to converting from mm to inches. I'd hope that by now you guys know there's 25.4mm to an inch. So 500mmHg vacuum is 19.7inHg, which is a pretty good idle vacuum.

 

i thought 1 bar was 14.7 psi?

 

Actually we're both wrong!

1kg/cm2 is 14.2psi
1bar is 14.5psi
1atm is 14.7psi.

 

goddamnit, I knew I was gonna get schooled again.

 

Mine is about 400 at idle, so thats what 15.7inHg?

 

Yep, sounds normal for an older engine.

 

Just divide by 25.4


-Ted

 

Except for the fact that the motor only has 4k miles on it....

But its a race ported motor.
should that make it a little bit lower?

 

Yes.

 

Seriously, the math has got to stop, I think my head is going to explode.