Jump to content
SAU Community

Quick Factory Boost Guage Question

Damo Monster

By Damo Monster,
in Engines & Forced Induction

 Share

Recommended Posts

Damo Monster Enthusiast

Damo Monster

Posted
Posted

hi there..

lately i have noticed that my factory boost guage in my 32 always seems to be showing a bit of boost, even at idle, its always under 0 at idle but it sits a bit above -7... the needle goes back down when the car is off so its not a stuck needle, but was wondering if this is common or if my turbo etc. could be stuffed?

cheers

Link to comment
https://www.sau.com.au/forums/topic/149090-quick-factory-boost-guage-question/
Share on other sites
fordman351 Apprentice

fordman351

Posted
Posted

Manifold vaccuum is exactly that, negative pressure (vaccuum) in the inlet manifold. The engine, while idling, does not produce enough exhaust gasses to spin the turbine, therefore the engine just draws air without the compressor forcing it in. Basically like an N/A engine would.

I think i just made a fool of myself :happy: , feel free to correct me, i'm here to learn too :D .

Damo Monster Enthusiast

Damo Monster

Posted
  • Author
Posted
Manifold vaccuum is exactly that, negative pressure (vaccuum) in the inlet manifold. The engine, while idling, does not produce enough exhaust gasses to spin the turbine, therefore the engine just draws air without the compressor forcing it in. Basically like an N/A engine would.

I think i just made a fool of myself :happy: , feel free to correct me, i'm here to learn too :D .

yeah i get what your saying there.. dont know enough myself to know if thats right or not but it sounds like it could be.. what worries me though is i've had the car almost two years and never really noticed it doing that before lol...

Damo Monster Enthusiast

Damo Monster

Posted
  • Author
Posted
www.howstuffworks.com

useful

yes i started reading some of that, and from the wikipedia site.. but i was more wondering why it does it and idle, and at 100km/ph, and yet i havent ever seen it doing it much before.. i was wondering if it meant my gauge has been a bit unreliable or if i should be getting the turbo looked at... but then again, it might be completely normal and i can go back to sleeping at nights lol...

JustinP Mentor

JustinP

Posted
Posted
yes i started reading some of that, and from the wikipedia site.. but i was more wondering why it does it and idle, and at 100km/ph, and yet i havent ever seen it doing it much before.. i was wondering if it meant my gauge has been a bit unreliable or if i should be getting the turbo looked at... but then again, it might be completely normal and i can go back to sleeping at nights lol...

I can assure you it's normal :(

mad082 Grand Master

mad082

Posted
Posted

if you have only just started noticing it, it may be that your gauge hasn't been working properly till now.

the vacuum is caused by the butterfly in the throttle body being shut, like holding your hand over the end of a vacuum cleaner, therefore it creates a vacuum in the manifold. as you open the throttle the vacuum gets less and less until you have the throttle open enough where the engine can suck in as much air as it is using (0 vacuum pressue).

that is a basic rundown on what happens.

RANDY Veteran

RANDY

Posted
Posted (edited)
lately i have noticed that my factory boost guage in my 32 always seems to be showing a bit of boost, even at idle

As mad082 says, that's vacuum. Boost is positive pressure, so anything less than 0 is vacuum.

Also note that the guage is in millimeters of murcury mmHg, not psi or bar or cowdung. ;o)

So... if you are cruising down a big hill and not accelerating, the engine is still turning quite quickly, and because of the compression in the cylinders, air is being pushed out the exhaust, but with the throttle closed it's hard for the motor to take any air in to match what is going out... subsequently, the vacuum in the manifold increases, and you get closer to -7mmHg (roughly 14psi) in vacuum.

Same thing at idle or slow cruising, but not as exaggerated as the above scenario.

Edited by RANDY
mad082 Grand Master

mad082

Posted
Posted

just so people with aftermarket boost gauges don't get confused, most aftermarket boost gauges read either psi or bar in positive, and most that read psi positive boost don't read psi in vacuum. in vacuum they read inches vacuum or something like that.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • sunsetR33
      Unpeeling the Orange

      By sunsetR33 · Posted

      Update 3: Hi all It's been a while. Quite a lot of things happened in the meantime, among other things the car is (almost) back together and ready to be started again. Things that I fixed or changed: Full turbo removal, fitting back the OEM turbo oil hardlines. Had to do quite a bit of research and parts shopping to get every last piece that I need and make it work with the GT2860 turbos, but it does work and is not hard to do. Proves that the previous owner(s) just did not want to. While I was there I set the preload for the wastegates to 0,9bar to hopefully make it easier for the tuner to hit the 370hp I need for the legal inspections that will follow later on. Boost can always go up if necessary. Fitted a AN10 line from the catch can to the intake hose to make the catchcan and hopefully the cam covers a slight vacuum to have less restrictive oil returns from the head and not have mud build up as harshly in the lines and catch can. Removed the entire front interior just shy of the dashboard itself to clean up some of the absolutely horrendous wiring, (hopefully) fix the bumpy tacho and put in LED bulbs while I was there. Also put in bulbs where there was none before, like the airbag one. I also used that chance to remove the LED rpm gauge on the steering column, which was also wired in absolute horror show fashion. Moved the 4in1 Prosport gauge from sitting in front of the OEM oil pressure gauge to the center console vents, I used a 3D printed vent piece to hold that gauge there. The HKB steering wheel boss was likely on incorrectly as I sometimes noticed the indicator reset being uneven for left vs. right. In the meantime also installed an airbag delete resistor, as one should. Installed Cube Speed premium short shifter. Feels pretty nice, hope it'll work great too when I actually get to drive. Also put on a fancy Dragon Ball shift knob, cause why not. My buddy was kind enough to weld the rust hole in the back, it was basically rusted through in the lowermost corner of the passenger side trunk area where the wheel arch, trunk panel and rear quarter all meet. Obviously there is still a lot of crustiness in various areas but as long as it's not rusted out I'll just treat and isolate the corrosion and pretend it's not there. Also had to put down a new ground wire for the rear subframe as the original one was BARELY there. Probably a bit controversial depending on who you ask about this... but I ended up just covering the crack in the side of the engine block, the one above the oil feed, with JB Weld. I used a generous amount and roughed up the whole area with a Dremel before, so I hope this will hold the coolant where it should be for the foreseeable future. Did a cam cover gasket job as the half moons were a bit leaky, and there too one could see the people who worked on this car before me were absolute tools. The same half moons were probably used like 3 times without even cleaning the old RTV off. Dremeled out the inside of the flange where the turbine housing mates onto the exhaust manifolds so the diameter matches, as the OEM exhaust manifolds are even narrower than the turbine housings as we all know. Even if this doesn't do much, I had them out anyways, so can't harm. Ideally one would port-match both the turbo and the manifold to the gasket size but I really didn't feel up to disassembling the turbine housings. Wrapped turbo outlet dumps in heat wrap band. Will do the frontpipe again as well as now the oil leak which promted me to tear apart half the engine in the first place is hopefully fixed. Fitted an ATI super damper to get rid of the worn old harmonic balancer. Surely one of the easiest and most worth to do mods. But torquing that ARP bolt to spec was a bitch without being able to lock the flywheel. Did some minor adjustments in the ECU tables to change some things I didn't like, like the launch control that was ALWAYS active. Treated rusty spots and surface corrosion on places I could get to and on many spots under the car, not pretty or ideal but good enough for now. Removed the N1 rear spats and the carbon surrounding for the tailpipe to put them back on with new adhesive as the old one was lifting in many spots, not pretty. Took out the passenger rear lamp housing... what do you know. Amateur work screwed me again here as they were glued in hard and removing it took a lot of force, so I broke one of the housing bolts off. And when removing the adhesive from the chassis the paint came right off too. Thankfully all the damaged area won't be visible later, but whoever did the very limited bodywork on this car needs to have their limbs chopped off piece by piece.   Quite a list if I do say so myself, but a lot of time was spent just discovering new shit that is wrong with the car and finding a solution or parts to fix it. My last problem that I now have the headache of dealing with is that the exhaust studs on the turbo outlets are M10x1.25 threaded, but the previous owner already put on regular M10 nuts so the threads are... weird. I only found this out the hard way. So now I will just try if I can in any way fit the front pipe regardless, if not I'll have to redo the studs with the turbos installed. Lesson learned for the future: Redo ALL studs you put your hands on, especially if they are old and the previous owners were inept maniacs. Thanks for reading if you did, will update when the engine runs again. Hope nothing breaks or leaks and I can do a test drive.
    • Kapr
      What brakes on R34 GTT(Europe)

      By Kapr · Posted

      No those pads are DBA too  but they have colors too. I look at the and imo the green "street" are the best.
    • wizlb
      Who has a Infiniti Q60, Q50 (V37)?

      By wizlb · Posted

      I’m not sure what happened I told them about sonic tunes free OTS tune and the next the I know .. I was booted..   To funny 
    • Kinkstaah
      Starting again

      By Kinkstaah · Posted

      Yea - I mean I've seen my fuel pump which is decades old and uh, while I'm not saying this with real knowledge... but I sure get the ick at using anything in the fuel system that produced the state of that pump. Many years ago I went through multiple pumps (and strainers) before I dropped the tank to clean it out with extreme violence. I'm talking the car would do maybe 50km before coming to a halt, which resulted in me cleaning out the filter with some brake cleaner and going on my way. None of my stuff ever looked like what came out of your fuel tank. I don't think I'd be happy with it unless every single component was replaced (or at least checked/cleaned/confirmed to be clean here).
    • GTSBoy
      What brakes on R34 GTT(Europe)

      By GTSBoy · Posted

      I'm not going to recommend an EBC pad. I don't like them. Just about anything else would suit me better. I've been using Intima pads for a while now.
×
×
  • Create New...