I installed a greddy boost guage today (x-mas gift) took it out for a spin and got a reading of exactly .5bar (7.35psi) my old autometer guage always read 8.7psi (.6bar) I switched them back out to make sure and I still get 2 different readings. My car has always been a little low on hp when I dyno it and I think I figured out why. Now I don't know what my boost really is or what guage I should trust. I'm thinking the greddy is right but one of them is wrong. I don't see how a company can sell a guage that's off by that much. 1.35psi might not seem like a lot but on a honda where 1psi=10hp and your trying to squeeze the max out of your motor and keep it safe it's a pretty big difference.

 

maybe the line is backed up on one of the gauges?

 

I have always heard that autometer guages aren't the most efficient gauges out there....I would trust the Greddy Gauge

 

is the greddy gauge mechanical or electronical?

 

Greddy gauge is electronic with a sending unit. Way better than the turdmeter. I used to have one (autometer) and after a month it wouldn't go back to zero. I guessed it was a bad unit and got another. Same thing happened in the same time frame. Got the Greddy and haven't looked back. No probs as of yet.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bulldogg83 &raquo;</TD></TR><TR><TD CLASS="quote">I have always heard that autometer guages aren't the most efficient gauges out there....I would trust the Greddy Gauge</TD></TR></TABLE>

I dont know why people say this...I have an autometer boost guage and it is dead on. I had a 5 psi spring in my Tial and it read right at 5 psi, then I switched to a 7 psi spring, and it stayed dead on 7 psi all the way to redline.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hoodwinked &raquo;</TD></TR><TR><TD CLASS="quote">

I dont know why people say this...I have an autometer boost guage and it is dead on. I had a 5 psi spring in my Tial and it read right at 5 psi, then I switched to a 7 psi spring, and it stayed dead on 7 psi all the way to redline.</TD></TR></TABLE>

because lots of people have problems with autometer, thats why...... lancer forums has a poll going right now to determine how many peeps boost gauges arent reading ANY vacuum... last time i checked it was 15% of the people who polled that had autometer gauges werent reading any vacuum... thats shows me they arent making very good products.... thats a very high percentage for just one type of problem

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hoodwinked &raquo;</TD></TR><TR><TD CLASS="quote">

I dont know why people say this...I have an autometer boost guage and it is dead on. I had a 5 psi spring in my Tial and it read right at 5 psi, then I switched to a 7 psi spring, and it stayed dead on 7 psi all the way to redline.</TD></TR></TABLE>

Maybe the gauge is good for low boost, I know for a fact that the gauge is crap id you see 15 plus psi. When i had an Eclipse, 27psi instead of 24 psi could have been very bad. I will never use an autometer gauge for anything important again.

 

What's your elevation? Electronic boost guages that read off the MAP sensor will read differently than Mechanical vaccume line guages when you are above sea level.

 

why would it be any different? With the electrical guage you're still tapping into a pressurized hose that see's the boost reading. Instead of traveling to the face of the guage though it goes to a sending unit mounted under the hood. That pressure is converted into an electrical signal, and that signal goese to the guage.

The greddy is right, I don't trust autometer. A friend of mine with a t2 noticed the same thing when he went to a better guage from the autometer.

 

If the Greddy unit is anything like a Stock MAP sensor, elevation will alter the Pressure reading. I think I have to explain this once a week...so here goes again.

When powered on, a Mechanical boost guage will read 0 psi at any altitude. A MAP sensor based Electronic guage will read the actual pressure at the given altitude.

Example, at 6000ft of elevation the Mechanical guage reads 0 psi. The Electronic guage will read -3psi, due to the elevation. Standard atmospheric pressure at sea level is 14.7, and 6000ft it is around 11.7. 3 psi difference. That is why at elevations above sea level, Electronic MAP based boost guages read differently than Mecnanical boost guages.

So, if the Greddy guages is feeding off a MAP based sensor, then elevation will alter your boost readings.

Judging by the 1.35psi difference, I'd guess that Tuscon AZ is a little less than 3000 ft.

 

Here's a chart I made stating the Elevation and difference from standard Air Pressure....aka, how much pressure you're losing at high elevations.

Elevation/Standard Air Pressure/Difference
0 14.7
500 14.43 -.27
1000 14.17 -.53
1500 13.91 -.79
2000 13.66 -1.04
2500 13.41 -1.29
3000 13.17 -1.53
3500 12.93 -1.77
4000 12.69 -2.01
4500 12.45 -2.25
5000 12.22 -2.48
5500 12.0 -2.7
6000 11.77 -2.93
6500 11.55 -3.15
7000 11.34 -3.36
7500 11.12 -3.58
8000 10.91 -3.79

 

I'm just curious...If autometer is such crap, then why do about all the pro's (Import and Domestic) use them in there race cars???

 

Is the elevation thing really true? I know the atmospheric pressure is different at my altitude but I always thought since it was reading the pressure in the motor it would be the same. What your saying makes a lot of sense though, you even guessed my elevation. Tucson is about 2600ft, the local track is 3075ft. This would correspond perfectly with your chart. So if this is true am I getting 7.3 or 8.7psi? I could confirm your theory by driving at a lower elevation and seeing what happens but that would be a long drive.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by flip1199 &raquo;</TD></TR><TR><TD CLASS="quote">I'm just curious...If autometer is such crap, then why do about all the pro's (Import and Domestic) use them in there race cars???</TD></TR></TABLE>

because its free , pros need sponsership

 

What, you think I'm just making this up?!?! Of course its true!

You are boosting 7.3psi worth of sea level air. If you drive at sea level, both your guages will read the same.

 

It would be great to compare them in Colorado, you would see nearly 3psi difference up there. I live at the base of a 9000ft mountain, maybe I will hook up both guages and drive up it to see what happens. Besides twisty roads are fun anyway.

 

Give it a try! If you hit the peak at 9000 ft, your Mechanical boost guage will hold steady at 8.7, and your electronic Greddy should read 4.2.