Boost Guage Questions
 

I have a blitz boost guage, and a blitz boost controller, that also measures boost for me.

I have noticed that my Blitz boost guage consistently reads 13PSI at full boost (as it should, this is what the car was dialed in at) while my boost controller hovers around 1.07-1.11 bar (15.5 PSI)

I was afraid something was wrong with the wastegate, so I have not really pushed the car for fear of over boosting. However, on the FWY the other day, a 2004 Porshce S, pulled up next to me, and...well..he was asking for it, so I obliged. After embarrsing him, I noticed a couple of things. 1 this is the hardest I have ever pushed the car to date. (I was at redline in 4th). 2 my boost controller read 1.24 bar, or 18.2 PSI. However, I did not blow the engine, nor did I detonate.

I think I have figured out why the 2 guages are showing different reading, however I want to hear from someone on the forum who has experience with this.

Should I be worried about the reading on the boost controller ?

Is my boost guage hooked at a different spot, and therefore, giving me a more accurate reading?

Which guage should I trust?

Any help for the RX 7 impared would be greatly appreciated :)

boost guage

Any one else care to elaborate?

well, i was thinking if your boost cont was plugged into a pressure line before the UIM where your boost gauge is, you could have a leak and thats whats causing the difference in pressure....BUT, if the boost cont is set for 13psi, and the turbos needed 18psi to make up for the leaks and show 13psi at the UIM, then wouldnt the controller limit the turbos to 13psi if thats where its hooked up? I dunno if that makes sense, so hopefully someone else can shed more light on the subject.

-Zach

If the gauge is at the intake manifold believe the gauge. Your boost controller is reading boost right from the turbo. Pressure drop in the intercooler causes manifold pressure to be lower than what actually exits the turbo. Pressure in the intake manifold is what counts; that's where you want to read boost.

This is exactly what I was thinking. Only took me 2 months to figure it out. :doh: and, I wanted to be sure.

Here is my question. I can see that my Boost Controller is plugged into my wastegate. So, I am guessing that the steel braided line is what is registering boost in the controller. Where do I look to see where my boost guage is connected? Is there a standard vaccuum line off of the manifold that is used?

the easiest place to hook up a boost gauge is one of the two nipples coming off of the passenger side of the UIM.

What kind of blitz boost controller do you have? I would believe the boost controller becauseits reading boost pressure from the same point (uim) as your boost gauge should (if you have it installed properly); therefore I would trust the boost controller as it adjust the boost pressure according to what the manifold pressure is. My boost guage and boost controller are pretty close in readings. Thats also assuming that you have the sbc-id or one just like it. The 18psi you saw is most likely a boost spike because the boost controller registers the highest boost pressure.

R.K.

On the controller, I think boost is being measured from the wastegate.

I don't follow your argument. In your example you say both read from the same point and then deduce that the boost gauge is wrong. How do you jump to that conclusion? Sounds like another case of "It's more expensive so it's more correct".

damon is right about the diff and press drop. what intercooler are you using? how was the car dialed in at 13 psi when the controller reads 1.x bar? did you use the gague to set it?

yeah all you do is trust the boost GAUGE, then up the boost on the controller until the GAUGE reads 13psi. You basically ignore the boost cont readout since its not reading the true PSI your engine is actually recieving.

agreed but if he did it that way why does he care now?

my guess is j/ out of curiousity. Ya kno the question "i know its supposed to be this way...but why?" :) Jesuscookies?

jesuscookies?

Neither,

I did not tune the car, or install the guage/controller. What happened is this, I was getting the readings from my boost controller, and was afraid that the wastegate was not doing what it was supposed to be, and that I was going to blow the engine. It did not dawn on me that the 2 could be hooked up at different spots, and so thought something was wrong.

Okay,

I just got home and went out and checked it. The boost controller has a little black box. One line is feeding in to it directly from the turbo, and then out (steel braided) directly to the top of the wastegate. So, it sounds like the boost is being sensed directly from the turbo..Duh :) (thanks for the clarification Damon)

Next problem, I cannot find where the boost gage is being plugged in at. I am heading back out to try and find this line.

Just plumb the boost controller boost line on the same line as the boost gauge and then compare the readings (thats the uim). I don't know about other boost controllers but the Blitz one has a seperate line to read boost pressure (thats the line you tap into the uim hence thats where the boost guage should also be tapped into).
Jesuscookies; the boost scencing line is tapped into the wastegate (its black in color)? Is that what you are saying? The only lines that should be coming off the wastegate are the in and out that go to the stepper motor. Hopefully I didn't confuse you or anyone else.

R.K.

stock there should be 1 line off the uim going to the air bypass valve. if there are 2 vac lines on the passenger side middle of the uim than that is the gague line.

Okay, I have 2 lines coming off of the UIM on the passenger side. One goes directly into my BOV. The other works its way thru the firewall under the glove compartment side. I think I should follow that line, to see where it is going into?

Again though, from what I can tell, it looks like the boost controller line is feeding directly off of the turbo. If I follow that line, and or take out the boost controller, I will be able to tell for sure.

Whaddya Think?

Remove the hose to the from the UIM. Cap it off. Start the car (dont drive it, of course), see if the gauge is registering vaccuum.

Just to be sure, check what the boost controller is saying. One would guess the installer might have T-ed boost controller into that same line...

Excellent, way eaiser than trying to follow the line thru the car....Thanks!!!!