Jump to content
SAU Community

Recommended Posts

My cold starts idle at around 10 on my wideband. I kind of actually can't stand the lean popping but I always thought it was something which shouldn't be happening. My car is sucking alot of air, -95 according to my profec b. My old car sat on around 85. When this one idles at 85, I know I popped off a vac line somewhere.

Ill take away some fuel and see what she does.

I have no idea. It reads positive boost, for example, as 100 which is 10.0psi. 155 would be 15.5psi. It reads vacuum as -95 on idle, -50 maybe on cruising, so I have nfi.

Most likely -9.6mmHg then, that is fairly low. My skyline reads about negative 14-15 and negative 20 when backing off at higher rpm.

Might be inches of mercury and not millimeters, and hence -0.99 inches, but that = -25mmHg which is far too high vacuum.

I'm stumped, it should be either of these units, I don't even know what else you can measure vacuum in. It is possible that 9.9 is just the maximum reading and it can't read any higher vacuum than that, when you back off at high revs does it read a number higher than 99 ?

99 is the highest number it reads in negative pressure, vacuum. Then it bounces back to idle. My other boost gauge shows -20 vacuum when on idle. For me I ignore these figures. I listen to the engine and I can hear if it's idling right and feel it through that chassis. Feels good as is.

It works like this .

You can't measure a vacuum because it is nothing zip zero zilch . Anything abouve a total vacuum is positive pressure even if it isn't as high as sea level atmospheric pressure here on earth .

The confusion exists because cork head humans got in the habit of measuring air pressure using two different base lines or datums .

1) Absolute Pressure Psi"a" . The correct way is to say a total vacuum is zero and anything above is positive pressure and it puts sea level airpressure at around 100 kpa/1000 millibars/14.7 psi (same). Some engine management systems read off absolute pressure with a manifold pressure sensor so 0 would be a total vacuum and 100 kpa sea level atmospheric pressure . Abouve 100 kpa is said to be positive pressure ONLY because its higher than atmospheric pressure . Anything from 1 to infinity is positive compared to absolute 0 .

2) Gauge Pressure Psi"g" . This is where pressure is referenced using sea level air pressure as 0 . When you have a compound gauge it trys to show you pressure thats lower than its 0 when the pressure is lower than atmospheric . They are really just a means of making a distinction between atmospheric pressure and anything thats added to it .

The silly thing is gauge pressure can make people think you can have a negative pressure when in fact technically speaking you can't have less than nothing .

From a tuning perspective I think absolute pressure (psia) is better to use because the graduations rising from absolute zero are easier to comprehend than ones rising either side away from an atmospheric pressure 0 datum .

Next time you look at a turbos compressor map pay attention to the pressure ratio (PR) scale . Because these pressures are a ratio of anything above atmospheric pressure to atmospheric pressure they will say for example PR = 2 when a compound guage shows 100 kpa/15 psi . This is because the first 1 bar (bar means barometric sea level air pressure) is just this and the second bar is the pressure above atmospheric .

An absolute pressure gauge would show atmospheric pressure as 100 kpa/15 psi and the second bar as 200 kpa/30 psi .

A .

Also explains why 20psi with all factors the same isn't double the air of 10psi, it is actually 24.7 and 34.7 psi, so a ~1.3x increase in air, not 2x increase in air.

And explains why you make less power the higher up a mountain you go.

Edited by Rolls

hey not sure if in right thread but since i have a hypergear turbo i thought id ask My atr43g3 turbo run at 18psi straight from the actuator but when i replaced the head gasket the exhaust cam was found to be 2 teeth out. Since i have put them back to proper timing car now boosts at 15psi Just wondering if thats happened to anyone else?

Less restriction, hence same airflow produces less boost. You are probably making the same power yes?

edit: You said exhaust cam not intake cam, it has now advanced the exhaust timing, hence less energy is wasted out the exhaust, the turbo then sees less energy and spools less hence less boost.

Makes sense to me, your car is probably running much efficiently, however it is probably slightly laggier in regards to boost response, it will flow better in the high rpm now though.

Your power curve will have shifted towards redline slightly, you will make more power though, that is if you get it retuned on 18psi, DEFINITELY get it retuned, the load points will have completely changed, you could be detonating driving it like that.

Edited by Rolls

Bugger another tuning session lol Makes sense though as the car is more lag down low but i haven't tried to feel whats up high

Also the tuner at the time overloaded the timing in the car by about 10 degress ( 35 degress at 6500 rpm ) I have backed timing off the whole chart down to 24 degress at 6500max after most of the spark plugs got destroyed with the head gasket.

but i haven't tried to feel whats up high

Don't, seriously don't load it up on boost at all until you get the tune checked. Won't cost much to tweak it hopefully, just depends how out it is now.

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



  • Similar Content

  • Latest Posts

    • 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.
    • No those pads are DBA too  but they have colors too. I look at the and imo the green "street" are the best.
    • 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 
    • 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).
    • 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...