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Discussion Starter · #1 ·
Hi all, just a question to those with aftermarket boostgauges / ebc's.

Some observations and questions!

1, when running in 4th gear (or third) with zero throttle applied, i.e cruising down a hill (coasting but in gear)...

What kind of vac pressure do you see?

2, the stock 'boost gauge' in the center cluster starts to move upwards before I am in boost condition (according to my ebc readout) I.e still slightly in vacuum, is this correct?

3, when driving (around town for example) at low rpm and slowly opening throttle, but not boosting, what kind of vacuum reading should I see?

Thanks all, noob question time over for now!
 

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Hi all, just a question to those with aftermarket boostgauges / ebc's.

Some observations and questions!

1, when running in 4th gear (or third) with zero throttle applied, i.e cruising down a hill (coasting but in gear)...

What kind of vac pressure do you see?

2, the stock 'boost gauge' in the center cluster starts to move upwards before I am in boost condition (according to my ebc readout) I.e still slightly in vacuum, is this correct?

3, when driving (around town for example) at low rpm and slowly opening throttle, but not boosting, what kind of vacuum reading should I see?

Thanks all, noob question time over for now!
Hi all, just a question to those with aftermarket boostgauges / ebc's.

Some observations and questions!

1, when running in 4th gear (or third) with zero throttle applied, i.e cruising down a hill (coasting but in gear)...

What kind of vac pressure do you see?

2, the stock 'boost gauge' in the center cluster starts to move upwards before I am in boost condition (according to my ebc readout) I.e still slightly in vacuum, is this correct?

3, when driving (around town for example) at low rpm and slowly opening throttle, but not boosting, what kind of vacuum reading should I see?

Thanks all, noob question time over for now!
1) I think that depends on speed, 4th gear at how many mph? Are we talking idle 1000ish rpm or 100mph like 5000 rpm?

2) The stock boost gauge is an appropriate reading according to the ECU based on the MAF, throttle position, and RPM. It's not actually a measuring device.

3) driving around implies variable rpm... It's hard to say. You need to factor many things like altitude parts and wear etc. Generally speaking 15-20 inches of mercury... Depending on several factors including if your AC is on... (additionally r12 or r334)


Perhaps you should ask what you're trying to accomplish instead of asking about specific things like vaccum measurements?




Sent from my LM-G850 using Tapatalk
 

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Discussion Starter · #3 ·
1) I think that depends on speed, 4th gear at how many mph? Are we talking idle 1000ish rpm or 100mph like 5000 rpm?

2) The stock boost gauge is an appropriate reading according to the ECU based on the MAF, throttle position, and RPM. It's not actually a measuring device.

3) driving around implies variable rpm... It's hard to say. You need to factor many things like altitude parts and wear etc. Generally speaking 15-20 inches of mercury... Depending on several factors including if your AC is on... (additionally r12 or r334)


Perhaps you should ask what you're trying to accomplish instead of asking about specific things like vaccum measurements?




Sent from my LM-G850 using Tapatalk
Sure so in instance 1,

Coasting down from 3k rpm to 2k rpm my boost controller shows 0 vac/boost so its neither in vac or boost.

2, yes, but dies the stick boost controller actually indicate vacuum below a certain level? I.e is the very bottom mark vacuum and 1/4 or 1/2 up when it starts to indicate boost?

3, I see variable vacuum as much as -8 psi (not 0.8, but 8 for example).
 

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I think based on your previous posts, you have a LCDBC, correct? If so my LCDBC will also show almost no vacuum during decel in some situations. For me specifically I'll let off and coast in gear, vacuum will spike up to around -11.4psi when I let off, then just show -.04 until I touch the throttle or fuel cutoff ends to return to idle.

At idle I'm around -9.2 to -9.4 with no load. A/C on it goes into the -8s. As for "cruising around and at part throttle but no boost" there really isn't a set number. It should be higher than your idle but lower than 0. Be aware that with TD04 turbos basically any throttle input above 2500rpms in 2nd+ gear is gonna get you into boost. For me even cruising in 5th gear at 70-75mph a slight touch of the throttle puts me in boost.

The stock boost gauge is accurate-ish for boost, but I find the vacuum reading to be entirely worthless.
 

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Discussion Starter · #5 ·
I think based on your previous posts, you have a LCDBC, correct? If so my LCDBC will also show almost no vacuum during decel in some situations. For me specifically I'll let off and coast in gear, vacuum will spike up to around -11.4psi when I let off, then just show -.04 until I touch the throttle or fuel cutoff ends to return to idle.

At idle I'm around -9.2 to -9.4 with no load. A/C on it goes into the -8s. As for "cruising around and at part throttle but no boost" there really isn't a set number. It should be higher than your idle but lower than 0. Be aware that with TD04 turbos basically any throttle input above 2500rpms in 2nd+ gear is gonna get you into boost. For me even cruising in 5th gear at 70-75mph a slight touch of the throttle puts me in boost.

The stock boost gauge is accurate-ish for boost, but I find the vacuum reading to be entirely worthless.
Thanks for the feedback.

I have a more basic unit than the full lcdbc, I can track my data via torque for example.

My boost/vac readings come from my HKS EVC 6 I just installed at weekend, and just wanted to see either how accurate it is or work out if I have a vac leak etc.

I'm going to build a proper vac leak tester from here:


I'm pulling -0.7 psi at idle so think.there is a small leak somewhere as it should be closer to -0.9 i think having read other threads.
 

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Discussion Starter · #7 ·
At idle you should be at -9 psi, not -0.9.
Hm I will go out to the car tomorrow morning and double check what I'm reading at idle.

The 3 ports on the top of the TB are fair game for vac readings right?
 

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Discussion Starter · #9 ·
the three on the top of the TB are not.

there should be one about 2 inches lower near the electrical connectors.
Great I've just ordered some more vac lines. The 6mm under the tb goes to my bov.

I will use the 4mm near the firewall and t that off to my FPR and boost controller vac line and cap the 3 on the TB and report back once done.
 

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If it was reading in BAR, then -0.7 would be closer to okay. AFAIK, the EVC VI can only be set to kPa or PSIg. You need a reading from the intake manifold.

-sent from my Galaxy Note 9
 

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Discussion Starter · #11 ·
If it was reading in BAR, then -0.7 would be closer to okay. AFAIK, the EVC VI can only be set to kPa or PSIg. You need a reading from the intake manifold.

-sent from my Galaxy Note 9
Hi yes I've set it in psi mode when I configured it

Will change my vac lines around tomorrow and see what it looks like then.

Thanks guys.
 

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Discussion Starter · #12 ·
At idle you should be at -9 psi, not -0.9.
Great news I replumbed my vac lines and now at idle I get -9.7 to -9.8 psi vacuum at idle.

I think that's about where it should be, with the lights on and 750 rpm idle it goes to above -10 psi.

I'm especially pleased as I replaced the plenum gasket and tb gasket and fitted my own egr block off plates my local garage made for me and redid all of my vacuum lines myself. And as I've said in other threads id never worked on any car before.
 

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I've had a vacuum gauge on every single car I've ever owned. I need to get off my ass and put one on the Stealth. Here's a handy chart that you can use for your vacuum/boost gauge. A vaccum gauge is probably the best device for diagnosis on an engine. It's what got me an A+ in auto shop. Don't leave home without one.

295315
 
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Discussion Starter · #14 · (Edited)
I've had a vacuum gauge on every single car I've ever owned. I need to get off my ass and put one on the Stealth. Here's a handy chart that you can use for your vacuum/boost gauge. A vaccum gauge is probably the best device for diagnosis on an engine. It's what got me an A+ in auto shop. Don't leave home without one.

View attachment 295315
Awesome mines showing a steady -10 now.

Just had my 3sx ss front pipe fitted:)

Part of my rear pre cat had melted and some fallen onto the main cat.
 
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