ScanGauge III

nix · **Posted:** Fri Jul 13, 2007 8:10 pm

I just got off the phone with the great folks at LinearLogic (the makers of ScanGauge II) and I was told that in 3 weeks or so they are releasing the ScanGauge III. I don't know all the details, but he said that it will be more programmable. He did mention that we can compensate the reading for the MAP sensor so you can make more sense of the reading. In my area, my MAP reads 14.2-14.7 psi at idle.. which is correct.. except nobody in the tuning world speaks in absolute pressure. (I want it to read 0 at idle) I asked him if owners of the older ScanGauge can send theirs in and upgrade the firmware. He said yes, for a $25.00 fee they will upgrade your SGII to a SGIII which includes shipping back. This was all a candid conversation over the phone.. so don't hold me to any details. Just thought you all would like to hear the gossip.

I installed my SGII today.. here are some shots of where I mounted it. I simply put the two pieces of velcro that came with the unit on the top of the SGII and stuck it to the head liner.. it sticks! Hasn't fallen once yet! LOL easiest install ever! :lol:

Cowcatcher · **Posted:** Fri Jul 13, 2007 9:47 pm

Great information!!! Thanks.

Kniggit · **Posted:** Sat Jul 14, 2007 4:39 pm

But, the turbo is at least turning a little and therefore making boost, what does the MAP sensor show with the key in the Run position but the engine not running?

K

nix · **Posted:** Sat Jul 14, 2007 5:40 pm

Kniggit wrote:

But, the turbo is at least turning a little and therefore making boost, what does the MAP sensor show with the key in the Run position but the engine not running?

K

At idle there is not enough exhaust flow to turn the turbo to make boost. It actually should register negative.

Cowpie1 · **Posted:** Sat Jul 14, 2007 8:05 pm

Not only that, but since is a variable vane turbo, even spinning, it would not be really forcing much if any air would it?

Kniggit · **Posted:** Sat Jul 14, 2007 11:39 pm

Actually, I thought that the whole purpose of the variable geometry was to keep the rotor spinning faster, more of the time, therefor creating a flatter boost curve.... I would still like to know if it reads anything with the engine off and the key in the run position. the big thing I am trying to say is if its under a vacuum at idle having the gauge read 0 would make the peak boost # larger than it really is. The correct way to calibrate it would be to set it for 0 while off, every time you start the car as its based on altitude, however thats a little ridiculous.

it may sound like over simplification but I'm an HVAC man and the easiest way for me to explain my thought on the still producing boost at idle is that when you spin the blower wheel in your furnace by hand at a small fraction of its usual speed it still moves air fairly efficiently, granted its turning at 1/10th the speed it usually would it is still moving air. This blower moves air with centrifugal forces with loose tolerances (like 1/2-1 inch) when you close the tolerances down to 1/16ths and 1/8th's like in the turbo what happens?

How much of the Vacuum at idle is being produced by the FCV? maybe even though you may be running the ORM its still partially closing. Just a thought.

K

TDI4BY · **Joined:** Sun Apr 02, 2006 11:56 pm **Posts:** 644

I think the difference is that there is nothing sucking air from your furnace like the engine does at an idle through the turbo. The turbo may be flowing air but not enough to make even the slightest amount of actual boost with the engine idling. Does that make sense?

chrispitude · **Posted:** Sun Jul 15, 2007 9:10 am

TDI4BY wrote:

I think the difference is that there is nothing sucking air from your furnace like the engine does at an idle through the turbo. The turbo may be flowing air but not enough to make even the slightest amount of actual boost with the engine idling. Does that make sense?

Exactly. To create pressure, the intake impeller must be spinning fast enough to feed more airflow volume than the engine would pull from an atmospheric pressure source.

- Chris

o8k · **Posted:** Mon Jul 16, 2007 1:18 am

If i may point out, all the issues you all are discussing about trying to zero out the SG are solved by just leaving the Absolute pressure reading alone in the first place, which is probably why they do it that way. =)

Wonder if the SGIII will have a fix in it so if the CRD putter locks up, it can re-est the connection w/ out having to stop the engine for a while. That would be very usefull.

o8k

jinstall · **Posted:** Mon Jul 16, 2007 4:34 am

Hmmm VERY INTERESED IN THE III. Waiting for it to appear.

skywarn · **Posted:** Mon Jul 16, 2007 9:24 am

Hey Nix -

looks like you have a "Engine performance light" on!

I gues in this case its gone form the "ORM" to the "DUO" (driveway use only) :lol:

nix · **Posted:** Mon Jul 16, 2007 10:39 am

skywarn wrote:

looks like you have a "Engine performance light" on!

Yep!!

I've already got the sequence of SGII buttons you have to press to reset the light down-pat. As a side note, I noticed the engine sounds louder at idle with the ORM.

Kniggit · **Posted:** Thu Jul 19, 2007 8:50 pm

Actually there is something "sucking" air out of the furnace, your house, but I do understand what you are saying. My real question is if someone has actually looked at the SG to see the #, start the engine look at the #, go for a drive and look at the number at idle, then shut off the engine and look at the #. That would be the only way to answer the debate.

K

nix · **Posted:** Thu Jul 19, 2007 11:32 pm

Kniggit wrote:

Actually there is something "sucking" air out of the furnace, your house, but I do understand what you are saying. My real question is if someone has actually looked at the SG to see the #, start the engine look at the #, go for a drive and look at the number at idle, then shut off the engine and look at the #. That would be the only way to answer the debate K

The scangauge will not power on with the engine off. With the engine on at idle the MAP sensor reads 15.2-15.8 depending on weather and altitude. Under full boost it reads around 35 psi. This equates to a real ~20 pounds of additional boost over atmospheric conditions which is about right for our CRDs.

Some interesting information pulled from nasioc (subaru forum)

nasioc wrote:

A short class (for the few that are interested) on how pressure gauges work. "A suffix of "g" will be added to a pressure reading whan it is a gauge pressure reading, likewise an "a" will be added for absolute pressure."

In theory, absolute pressure (Pa) is the gauge pressure (Pg) plus standard pressure at STP (sea level standard temperature and pressure)...
Pabs[psia] = Pg[psig] + 14.7psi ----- or ----- Pg[psig] = Pabs[psia] - 14.7psi.

For reference, absolute pressure (@ STP 25 degC/77degF, to 2 sign. digits):
1.00 atm
1.01 bar
14.70 psi
0.10 MPa
760 mmHg

In reality, a gauge pressure is adjusted relative to the ambient pressure/temperature conditions that it was calibrated in. For example, If your pressure gauge was "zero calibrated" in Denver CO, at 13.5 psia, your "Denver, CO relative absolute pressure" would be 13.5 higher than the pressure read on the gauge (or your "gauge" pressure). If the same car was turned off at sea level, the gauge would read 1.2 psi (at 1atm/760mmHg/14.7psi Standard Temperature and Pressure - STP). Just remember that your gauge is always relative to the conditions it was calibrated in.

Unless of course your gauge says [psia] in the units (most don't though), then your gauge would read 14.6-ish when the car is off(give or take for climate and altitude).

The same goes for vacuum...you can't pull more than 14.6 psi of vacuum at ambient STP conditions (this is called absolute vacuum). In reality, you won't get even close to half-absolute vacuum (7.3 psia). As a comparison, most boost gauges read 30-40 mmHg vacuum.

30mmHg(vac)=0.04atm=0.58psi=0.04bar
40mmHg(vac)=0.05atm=0.77psi=0.05bar

Kniggit · **Posted:** Fri Jul 20, 2007 1:10 am

I took Chemistry, and Auto Mechanics in High School and graduated in 99 so the whole absolute pressure thing is not new to me. However if you read the quote above and as you said the reading is 15.2 that would be .5 psi boost if the number that Nasioc used is correct, which iirc, it is. I was not aware of the fact that it would not read any sensors with the engine not running. Not that I want to start a major flame fest or anything stupid, But that looks to me like it is creating boost even at idle.

K

GregScuba · **Posted:** Mon Jul 23, 2007 3:13 am

IIRC, atmospheric pressure is approximately 14.7 psi, no?

Kniggit · **Posted:** Mon Jul 23, 2007 2:11 pm

Thats what you use when you measure in atmospheres so to put it in plain English 15.2-14.7=.5psi boost at idle.

or if you like the Wikipedia approach "A column of air 1 square inch in cross section, measured from sea level to the top of the atmosphere, would weigh approximately 14.7 lbf."

K

ScanGauge III

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