SwooshMan

Ok so stock boost is 5.5 psi(w/o stock boost controller). Is that MAP or gauge pressure? My microtech is reading about 4 psi and my boost gauge is reading a little less than half a bar. Thats normal due to my elevation(4000+ feet). I'd like to turn the boost to 8-10 psi but should that be the reading on my gauge or the Microtech? I guess a simpler question that will answer my question is does stock boost change with elevation? Thanks for any help.

J-Rat

iTrader: (2)

Stock boost should not change due to elevation.

SonicRaT

iTrader: (6)

Stock boost is 5.5psi (with no boost controller) because that's what it takes to open the wastegate. The MBC just increases the pressure required to open the wastegate. This makes more boost.

SwooshMan

It will be harder for the turbo to make that amount of boost though, correct? This is the way i've had it explained to me, "the turbo will be making about 2 psi (@4000ft) more than the motor will actually see b/c it has to overcome the lower air density". I can hear my turbo spool before the microtech see's any boost but the greddy gauge already shows boost. The most i've seen my microtech reading is 4 psi but the gauge is going up to a tad below .5 bar. I had to turn the make the spring on my Blitz bov as soft as possible to get it to work all the time and only making 4 psi would explain that. Keep in mind that i have no idea what my boost should feel like b/c this car used to be N/A and this is my first turbo car. Here is an exerpt from the AEM's EMS Instructions that i was directed to when i was trying to figure out why i was getting two different readings.

"Pressure is measured in two ways: one is absolute pressure, and the other is gauge pressure. The difference between these is where the zero point of each scale starts. With absolute pressure, zero is a complete void of all pressure. With the more common gauge pressure, zero is at standard atmospheric pressure (14.7 psi). Anything below 14.7 psi is referred to as vacuum and anything above that is referred to as boost or positive pressure. Closed or very small throttle angles are associated with low manifold pressure (a vacuum on the gauge measuring style), and large throttle angles or full throttle is considered high manifold pressure (0 on the gauge measuring style). Typical boost or vacuum gauges used in automotive applications use the gauge type of readout. In automotive engineering, the absolute method of measuring pressure is used."

So basically my gauge is going to read a couple of lbs more than the Microtech b/c its not reading absolute pressure. So when i'm setting my mbc for a safe boost level should i use the reading on my boost gauge (Greddy Electrical) or the Microtech? I'll only have use of a wb for a few hours and i would like to be prepared before hand. Also, was is the accepted safe boost levels for the stock turbo with stock(professionally cleaned) injectors? Please feel free to set me straight if i'm out in left field!!! Thanks again.

RETed

Yes, altitude changes boost characteristics.

If the EBC is NOT closed-loop MAP (has it's own dedicated boost sensor with feedback), it will boost lower at higher altitude.

This is normal.


-Ted

SwooshMan

I just have a tuboxs mbc, the "high perfomance" one, not the dual stage but the one with two adjustments. Am i thinking about things the correct way?

J-Rat

iTrader: (2)

At 4000 ft, you shouldnt see any difference. I never saw one at 3100 ft..

SureShot

If you really want to know how altitude effects boost talk with an aircraft mechanic.

Supercharger boost results are tied to relative pressure.

In general boost gauges show absolute pressure (like a barometer).

Manual boost controllers correspond in reverse to relative pressure.
They let off more at altitude since they have ambient air on the outside of the valve.
That somewhat negates the altitude loss of the supercharger.

MountainTurbo

I have the same type of thing going on in my car at about 4-4500ft elevation. My aftermarket boost gauge will read 6-8psi, but my EBC will only read 4-6ish psi. When I go to high boost mode, the gauge will read 10-12, but the EBC will read 8-10.5.

OverDriven

Let me guess...is it an Autometer gauge?

-Joe

SwooshMan

I have a electronic Greddy so i know that is not the problem. When I turn my car, on a boost gauge starts at zero, which is not absolute pressure. The microtech reads absolute pressure which at my altitude is about 5in of vacuum. This is with the key on and the car not running. This is how it should be. If you want more information about the differences between MAP and Gauge pressure read the MAP info in the AEM Ems instructions. Here's a link. http://www.scuderiaciriani.com/rx7/A...asics_V1.3.pdf

Falcoms

Altitude has everything to do with boost. As you go higher, the thinner the air is (less air molecules per square inch). Therefore, there is less air for your turbocharger to compress, therefore you have lower boost pressure.

SwooshMan

Thats what i thought. Thanks.