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    Boost readings on a standard 850 dash gauge how do they compare?

    So having the car tweaked after the engine build it got me wondering about the readings the standard 850 dash boost gauge shows approximately. I have pondered over getting an aftermarket gauge but tbh I donít like the add on look of a pillar mounted pod so never have seriously looked into it. We all know as a general rule of thumb that the end of the white section is around 1 bar of boost or 14.7 psiÖ. or is it?

    I had occasion this weekend to fiddle with a calibrated mitivac tool, which is generally used to check vac and pressure systems, indeed it is a very useful tool for checking wastegate actuators for leaks and spring strength. I decided I would check the dash gauge at various pressures to help anyone else who has wondered the same especially those who are trying to fault find but perhaps donít have access to a good boost gauge.

    So here is the first pressure shots, this shows approximately .25 bar of boost (or 4 psi) which is the general pressure you would expect a good condition wastegate actuator to start opening if itís not bypassed by either a BCS, MBC or otherwise. This is the pressure you should see if you take the rubber vac pipe straight from the compressor housing and plumb it into the actuator. Even on high boost cars the actuator should still be opening around now but the boost controller, MBC, BCS should bleed pressure away from the actuator to stop the wastegate from opening and therefore obtain the boost reading wanted.





    As you can see on the dash gauge this represents little to no boost reading. On a standard car or a modified car that still runs a BCS the most likely cause of boost pressures not exceeding this level will be due to a BCS fault, of course there can be other reasons as well.

    So 1 bar of boost (14.7 psi) is the end of the white section is it? I think notÖ





    As you can see the gauge is still sitting within the white section. I believe you would be lucky to see this boost level on a standard unchipped 850 because Iíd expect the boost cut to have tripped in by now if the maf is reading air flow correctly.

    Chipped, Rica or similar usually allow boost levels of up to or around 1.2 bar (17.6 psi), this shows the gauge reading at 1.2 bar which is just outside the white section.





    Russ tells me mines now set to boost and hold a maximum of 1.45 bar (21.3 psi) which looks like this and tbh is spot on what I am seeing when using moderate to hard throttle applications.





    Then for fun I pressed on up the pressure scale.

    1.7 bar (24.9 psi)





    1.8 bar (26.5 psi)





    Hopefully some people will find this of good reference for boost fault finding and others may just find it interesting. Anyone who does have boosting issues and decides to investigate I would always recommend enlisting the help of someone in the know and utilising accurate equipment for checking boost levels, anyone who decides to utilise there standard gauge and cross references against my findings with my gauge does so at their own risk as I won't be funding any engine builds...


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  2. The Following 18 Users Say Thank You to AndysR For This Useful Post:

    claymore (Saturday 8th March 2014),Jamest5r (Sunday 16th February 2014),jdavis (Wednesday 25th March 2015),JT (Sunday 16th February 2014),martybelfastt5 (Thursday 26th March 2015),MoleT-5R (Sunday 16th February 2014),Nealevo (Sunday 16th February 2014),oblark (Sunday 16th February 2014),RollingThunder (Monday 17th February 2014),S.Herb (Wednesday 19th March 2014),Saaamon (Sunday 16th February 2014),Shinsplintz 101 (Sunday 16th February 2014),smithy (Sunday 16th February 2014),sunny scott (Sunday 16th August 2015),t5 pete (Sunday 16th February 2014),theflyingbrick (Sunday 16th February 2014),thesoundcriminal (Wednesday 25th March 2015),woz (Wednesday 19th February 2014)

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    Nice one Andy never seen that done before, mine goes to 3 o'clock which is about right, does the gauge go past this point or is that the max of its rotation?


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    Quote Originally Posted by Jamest5r View Post
    Nice one Andy never seen that done before, mine goes to 3 o'clock which is about right, does the gauge go past this point or is that the max of its rotation?
    Tbh 1.8 bar was as high as I dared go as I didn't want to bugger up my dash.. I suspect it probably goes further as it didn't seem to hit a stop at that point..


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    at this level on my boost gauge was reading 13 psi


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    Quote Originally Posted by T5frankie View Post
    at this level on my boost gauge was reading 13 psi

    Was your boost gauge professionally calibrated?


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    Quote Originally Posted by AndysR View Post
    Was your boost gauge professionally calibrated?
    yes it was plugged in by me lol, i dunno how accurate it was its a digital one

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    going by Andy's pics, I used to be able to get mine around to 21 psi but it died of and I've not sorted it to get it back there, wish I could it moved like a cat on hot coals then, I need that speed again.

    Great reference Andy, thanks

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    Quote Originally Posted by AndysR View Post
    So having the car tweaked after the engine build it got me wondering about the readings the standard 850 dash boost gauge shows approximately. I have pondered over getting an aftermarket gauge but tbh I donít like the add on look of a pillar mounted pod so never have seriously looked into it. We all know as a general rule of thumb that the end of the white section is around 1 bar of boost or 14.7 psiÖ. or is it?

    I had occasion this weekend to fiddle with a calibrated mitivac tool, which is generally used to check vac and pressure systems, indeed it is a very useful tool for checking wastegate actuators for leaks and spring strength. I decided I would check the dash gauge at various pressures to help anyone else who has wondered the same especially those who are trying to fault find but perhaps donít have access to a good boost gauge.

    So here is the first pressure shots, this shows approximately .25 bar of boost (or 4 psi) which is the general pressure you would expect a good condition wastegate actuator to start opening if itís not bypassed by either a BCS, MBC or otherwise. This is the pressure you should see if you take the rubber vac pipe straight from the compressor housing and plumb it into the actuator. Even on high boost cars the actuator should still be opening around now but the boost controller, MBC, BCS should bleed pressure away from the actuator to stop the wastegate from opening and therefore obtain the boost reading wanted.





    As you can see on the dash gauge this represents little to no boost reading. On a standard car or a modified car that still runs a BCS the most likely cause of boost pressures not exceeding this level will be due to a BCS fault, of course there can be other reasons as well.

    So 1 bar of boost (14.7 psi) is the end of the white section is it? I think notÖ





    As you can see the gauge is still sitting within the white section. I believe you would be lucky to see this boost level on a standard unchipped 850 because Iíd expect the boost cut to have tripped in by now if the maf is reading air flow correctly.

    Chipped, Rica or similar usually allow boost levels of up to or around 1.2 bar (17.6 psi), this shows the gauge reading at 1.2 bar which is just outside the white section.





    Russ tells me mines now set to boost and hold a maximum of 1.45 bar (21.3 psi) which looks like this and tbh is spot on what I am seeing when using moderate to hard throttle applications.





    Then for fun I pressed on up the pressure scale.

    1.7 bar (24.9 psi)





    1.8 bar (26.5 psi)





    Hopefully some people will find this of good reference for boost fault finding and others may just find it interesting. Anyone who does have boosting issues and decides to investigate I would always recommend enlisting the help of someone in the know and utilising accurate equipment for checking boost levels, anyone who decides to utilise there standard gauge and cross references against my findings with my gauge does so at their own risk as I won't be funding any engine builds...
    mine boosts to 1bar on boost gauge with no mbc fitted is mine a chipped ecu?

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    Mine boosts to just off the second dash picture and doesn't fuel cut since changing to a different maf.

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    Quote Originally Posted by richyt5 View Post
    mine boosts to 1bar on boost gauge with no mbc fitted is mine a chipped ecu?
    Running 1 bar of boost it won't be a standard ecu that much is certain, unless there's an mbc fitted and you've not found it?

    Quote Originally Posted by Saaamon View Post
    Mine boosts to just off the second dash picture and doesn't fuel cut since changing to a different maf.
    Not sure what the actual boost cut is for a standard ecu but you can't be far off?


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    Another excellent thread revival following a search after my comments last night on the perceived inaccuracy of my own dash boost gauge.

    Here's the thread: http://www.vpcuk.org/forums/showthre...188#post765188

    I don't have the easy ability or inclination to really check the accuracy of the gauge as shown above, but any suggestions on simple or common things to check are welcomed

    Butt dyno and comparative speeds against markers suggest performance is virtually on a par with my previous MR2 Turbo Rev 3 which was 1240kg 270bhp. The 850 is definitely quicker in a straight line than my S2000, ATR, Clio RS200 Cup etc

    My video was taken on a dead flat road, I have noticed that up hill it seems to boost a little harder, I'm assuming this is normal and somehow load dependent?

    Thanks in advance for any assistance. Can't be missing out on any boost, so good to ask.
    Last edited by kmb; Wednesday 25th March 2015 at 11:49.

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    Wow no wonder my olive T-5R is such fun at present, the new ecu is letting the 15g give her 21-24 psi going by Andys pic's, might have to turn that down a bit or just not get too carried away at low revs.

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    That sounds 'rather' high, sure to be fun though... as long as it doesn't end in tears

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    Quote Originally Posted by kmb View Post
    That sounds 'rather' high, sure to be fun though... as long as it doesn't end in tears
    Got a spare T-5R and a new engine under way... , but I think I'll just be careful and maybe wind the actuator back a tad...

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    Just a quickie - How long does it take to wind the actuator a turn or two?

    If my gauge is to be believed and the detailed pipework inspection doesn't throw anything up I might consider moving a little closer the end of the gauge with a twist of the actuator

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    Quote Originally Posted by kmb View Post
    Just a quickie - How long does it take to wind the actuator a turn or two?

    If my gauge is to be believed and the detailed pipework inspection doesn't throw anything up I might consider moving a little closer the end of the gauge with a twist of the actuator
    that will depend on whether you still have the heat shield in place, if not it's a 5-10 minute job, slacken the locking nut and remove the pin and pull the arm off, you can then turn it clockwise to tighten/ increase the pressure required before the wastegate will open, or anti-clockwise to slacken/ reduce the required opening pressure. When you pull the arm off, if it set is set as standard and you rest the arm on top of the pin of the closed wastegate arm, the hole will be about half way across the top of the pin, so you have to stretch the arm over the pin to re-fit it.

    Obviously if the heat shield is still in place the job will be quite a bit longer as you'll have to remove it to access the wastegate end of the actuator and I would advise half or a whole turn only, then road test and only then adjust further by one turn or a half turn at a time, as we won't want something nasty to happen, a nice and steady approach is the safest with this this tweek.

    p.s. don't forget to tighten the locking nut when you've finish, as it can come off, as I found out once

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    This sounds good, without seeing the part under the heatshield (any photos could be great), this really doesn't mean a lot yet... but certainly a fun way to spend some tinkering time

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    Quote Originally Posted by kmb View Post
    This sounds good, without seeing the part under the heatshield (any photos could be great), this really doesn't mean a lot yet... but certainly a fun way to spend some tinkering time
    I'll get a pic up later, but for now I've got to get some of the kitchen completed before the mrs's gets back as she'll guess I've been on here too much today....lol

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    I'll go and take a picture now, hang on 5 minutes.

    EDIT: ok, ignore the external spring.



    and here's a turbo off the car.

    Last edited by claymore; Wednesday 25th March 2015 at 16:49.
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  30. #20
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    Quote Originally Posted by claymore View Post
    I'll go and take a picture now, hang on 5 minutes.

    EDIT: ok, ignore the external spring.



    and here's a turbo off the car.

    I do love your extra spring approach, cheaper and easier than ordering an uprated or adjustable actuator and having then to await it's arrival before being able to fit it, bamm! job done....

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