K-Train04RL

iTrader: (1)

hey guys, im just wondering if i have a vac leak. at idle i only see about 60-70 kpa vac. my lsj saturn redline sits at like 19psi and i know thaat 60-70 kpa vac is alot less than 19 psi. stupid kpa gauge.

CannonBalt

60-70 KPA is only 8-10 PSI, When I am at idle with my 2.0L LSJ I see 18-22PSI Vacuum... Which is 130-150 KPA

emiller

18-20 once its warmed up.

JetBlackSS

iTrader: (5)

Is this on the stock gauge? My interceptor was only reading like 10-11 psi on idle but I put in a stock gauge and im seeing 18-21 psi at idle.

SSlobalt

You're just doing the conversion incorrectly. -70 kilopascals is the same as -20 inches of mercury, which is the units on the stock gauge. It's not psi.

You do not have a vac leak.

Edit: Corrected for tom.

tomj77

iTrader: (2)

holy cow, u guys in boost at idle, i see -20psi when car is out of warmup mode. should be within a few of -20 normally, if its lower than that like -30, something is wrong

K-Train04RL

iTrader: (1)

rofl sorry forgot the -... and also thanks i figured i was doing something wrong with the conversion. didnt seem right to me. but i never checked my vac before i put on my charge pipes. thanks.

SSlobalt

No problem. There's a reason they pay me so much to give advice on this site.

K-Train04RL

iTrader: (1)

hah. ye i try and help, im only an appentice tech, so im not the most knowledgeable but im around car all day. wasnt sure about this though. this kpa crap is screwing me up lol. going to change the gauge out for psi. i was asking about the leak cause i want to get in touch with the local tuner and get some power now that i have the supporting mods.

tomj77

iTrader: (2)

ur conversion is right, but -10 is a little odd. does it do that right at start up or when its been sitting 5 minutes, cause at startup it is at about -10 and it slowly goes to -20 psi

K-Train04RL

iTrader: (1)

Read above. I'm fine. Asked my master tech how/why etc and he gave me the run down. Even set up a scanner to show my vac at idle in psi.

09CobaltSS1

lmao.. you will never ever see a negative psi figure from a pressure gauge on an engine!!

Sorry, I don't mean to be a literal ass, but it just drives me nuts when guys say, "I'm seeing -18psi at idle (lol@ you guys who say idol btw!), does this mean I have a vacuum leak?"

Most standards for measuring vacuum is in inches of mercury (inHg), or inches of water column (inWC). In the automotive world it's pretty much exclusively measured in inches of mercury. Got it? Good! lol..

Stamina

I get what you're saying, but some gauges don't do that. For instance, I can't set up a virtual gauge on the Dashdaq that combines two different units of measure on the same virtual gauge. I chose to keep things psi, and although it's not correct, it's not like it's hard to convert between them.

09CobaltSS1

I hear ya man, that's sort of different though. Making a custom pid in your dashdaq or even logging software to read a unit that you prefer is one thing. Really my point wasn't to try to make someone feel stupid but to point out a misconception and misunderstanding people tend have about what vacuum is and how to read a boost/vac gauge.

To say you're seeing -20psi or even 20psi at idle is just silly to me. Negative psi isn't even a real unit of measure and 20psi is just.... oy.. lol.. . You can't actually measure negative pounds per square inch but you can make a digital gauge read a negative number like you are. Honestly, kpa is really the way to go usually, but that's even further misunderstood by us stupid americans..

Stamina

Maybe we should just forget it and stick to inHg, like aircraft. Logical, comparable value every time, no matter what altitude. Plus, it'd just be cool to say something like "Yeah, I'm running 77 inches Mercury manifold pressure right now... " lol

SSlobalt

Where I work, all of our vac readings are in mmHg.