Wuz up my peeps! I wuz straight chillin when all of a sudden my ride blew up! I wuz like, Ohh shnap!

Hahaha jk.

I installed my boost gauge today, and this one reads vacuum. So at idle it reads at about -7psi then goes up as I accelerate. Is that correct? I know this is a stupid question, but i'm new at this whole boost thing and want to make sure this is right.

Here's a pic of it. Yup! displays the pressure in bar (kg/cm2) cause i'm cool like that yo!

 

as far as I know, it should because your car makes vaccume in the manifold when the throttle body is closed...and NA engines will read close to 0 at full throttle...what the turbo or supercharger adds is the positive pressure

 

Since superchargers work mechancially,the boost will be a little different than with a turbo.
You can wind out a turbo engine without boosting above atmoshperic,just depends on the throttle position.With a supercharger,its all about RPMS,so you should see something above 0, after hitting 2-3KRPMS.Some superchargers have a bypass,so it can vary a bit,but youll always be pulling vacuum at idle and usually till about 2K RPMS.

 

Cool deal! Steve, thanks for explaining because thats exactly what's going on, so it must be right. I'm learning though. Thanks guys.

 

I need to get off my *** and hook mine up.

And you shouldn't make titles like that... I was grief striken and paniced all at once... such a nice FB. Buy you lied, and well, that hurts.

 

-.7 BAR sounds about right for idle. at least its okay.

 

Sorry, didn't mean to hurt you. I was just trying to prove a point. LOL

Nahh, you guys always hook me up. I can't complain.

 

A little higher than that, actually -.5 bar.


Hmm? I need to get off my *** and install the rest of the gauges too. It's too fricking hot though.

 

get a gauge that reads lbs not bar,lol

its gotta get some sorta vacuum somehow.

where did you hook the gauge up too?



hows the powah nucka?????

 

We're talking about vacuum so -0.5bar is less then -0.7bar.

-0.5bar is about right. Could be a bit higher but it depends on a few things like idle rpm and porting. Some gauges aren't always dead accurate either.

 

Now you're screwed, how are you going to tell what time it is without the clock?

 

bar boost gauges are retarded unless you live in a country where thats common,

yeah dog my **** is mad jay dee emm ****...

 

Why is it retarded? It still gives you the same information.

 

It isn't retarded at all. Its all the same. The only thing psi is compared to bar is bragging rights. "Oh I hit 15 psi" Just because we live in America doesn't mean anything. If all you are doing is using a gauge for what it is meant to be used for, it doesn't matter if it is in bar or psi. If you can read it, then its doing its job.

 

What is its job in a NA set-up?

 

Thanks for correcting me REVHED. I meant lower.

saltyslug, I hooked up the sender to a port on the sc that's meant for a gauge, that's where all the others w/ sc's hooked their senders to. Power is not there, Still breaking it in and still waiting on parts to tune my carb. Hell, I haven't even put 50 miles on her yet.

purple82, my Alpine has a clock, so i'm good.

rotary_sex, bar is not retarded, why would you say that? 0.2 bar = about 2.90psi, 0.4 bar = about 5.80 psi. See, not retarded, easy to figure out, yo.

Plus my bar gauge lights up 7 different colors. (not that it matters cause i'm going to use orange) A friend of mine picked that one up for me along with these from Europe:


And here's a pic of how my gauges will look to match, thanks Scott!

 

ummm I have usually about 15 lbs of vaccume at idle. you might have low compression. Make sure it's hooked up to a vaccume signal off of both rotors or it'll bounce.

 

1 bar=14.6959409 psi, or 1 atmospheric pressure. BAR is short for BARametric pressure,or the amount of pressure that the atmosphere presses on yous guys.

Unit Equivalent measurements

Pounds per square inch (psi, PSI, lb/in2, lb/sq in): Commonly used in the U.S., but not elsewhere. Normal atmospheric pressure is 14.7 psi, which means that a column of air one square inch in area rising from the Earth's atmosphere to space weighs 14.7 pounds.

Atmosphere(atm): Normal atmospheric pressure is defined as 1 atmosphere. 1 atm = 14.6956 psi = 760 torr.

Torr(torr): Based on the original Torricelli barometer design, one atmosphere of pressure will force the column of mercury (Hg) in a mercury barometer to a height of 760 millimeters. A pressure that causes the Hg column to rise 1 millimeter is called a torr (you may still see the term 1 mm Hg used; this has been replaced by the torr). 1 atm = 760 torr = 14.7 psi.

Bar(bar): The bar nearly identical to the atmosphere unit. One bar = 750.062 torr = 0.9869 atm = 100,000 Pa.

Millibar (mb or mbar)" There are 1,000 millibar in one bar. This unit is used by meteorologists who find it easier to refer to atmospheric pressures without using decimals. One millibar = 0.001 bar = 0.750 torr = 100 Pa.

Pascal(Pa): 1 pascal = a force of 1 Newton per square meter (1 Newton = the force required to accelerate 1 kilogram one meter per second per second = 1 kg.m/s2; this is actually quite logical for physicists and engineers, honest). 1 pascal = 10 dyne/cm2 = 0.01 mbar. 1 atm = 101,325 Pascals = 760 mm Hg = 760 torr = 14.7 psi.

Kilopascal (kPa)" The prefix "kilo" means "1,000", so one kilopascal = 1,000 Pa. Therefore, 101.325 kPa = 1 atm = 760 torr and 100 kPa = 1 bar = 750 torr.

Megapascal (MPa): The prefix "mega" means "1,000,000", so one megapascal = 1,000 kPa = 1,000,000 Pa. Such high pressures are rarely encounterd.

Gigapascal(GPa): The prefix "giga" means "1,000,000,000", so one gigapascal = 1,000 MPa = 1,000,000 kPa = 1,000,000,000 Pa = 9,870 atm = 10,000 bar. Pressures of several gigapascals can convert graphite to diamond or make hydrogen a metallic conductor!

 

Hyper: You probably mean 15"Hg vacuum. 15psi would be beyond a perfect vacuum. 0.5bar is close to 15"Hg. I get about 0.7bar vacuum on my stock SE (28kPa absolute pressure out of 98kPa barometric pressure). The vacuum you get depends on porting, timing, mixture... Bigger ports will have less vacuum.

Kim: Looks good. You had me worried with the tittle, though.

 

I have been watching this thread, waiting to see how long it took for someone to post that here we measure vacuum in Hg. Thanks Addict.

You are correct on the porting, as is Hyper on balancing the signal from both rotors. When I first had the bp running, my vacuum gauge was plumbed to the rear primary intake runner. At idle, the needle vibrated so fast from the overlap, it was a red blur on the dial.

This was with the stock exhaust, before the 3" was installed. It is still plumbed the same, but the 3" exhaust has toned down the overlap and I can read the gauge now. With the porting done on the engine, my vacuum runs around 8" Hg at a 1300 rpm idle. compression is over 115 on all faces.

 

Thanks guys for the info. The sender is hooked up to a port on the sc manifold. I have to fix my other vaccum lines too ( I got a mess going on there) Plus it's not tuned yet (this weekend, yay!) I will report what I come up with.

 

those sum sexy gauges where bouts are they going
sorry if its been stated

 

I have an extra center that i'm going to cut off the part where the temp ***** and clock are on, then mold it on my center in the space where the radio hole is. Should come out nice.

 

Yes, it is best to plumb the vacuum line into the plenum (it there is one) or to tee the signals from both rotors. Now for people running big ports (bridge, peri, etc.), there are a couple tricks to measuring vac. These engines tend to have low vacuum, and the vacuum signal changes substanitally (as in trochoid's experience). You can tie the signals from the two rotors together, then connect to a container (such as a fuel filter) and then add a resitrictor (people use the nozzle part from a MIG welder sometimes). The fuel filter acts as a capacitor and the restrictor acts as a resistor. The two dampen the fluctuations in the vacuum signal. You may have to adjust the size of the restrictor to balance good response of the signal, but not have too severe of fluctuations. This is quite important for people running these ports or a large cam with aftermarket EFI that uses MAP, but could be used to get a smoother signal to your vacuum gauge.

 

I have a question related to all of this...

Should a freshly rebuilt rotary produce similar manifold vacuum to what a piston engine does?

ie; my beater Altima makes 20 inHg all day long at idle, with little to no maintenance, while usually for a piston engine anything above 17 inHg is acceptable. Should I see something in the same range with my 12a?