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Discussion Starter · #1 ·
I recently purchased a rather cheap mechanical boost gauge to get me started (first turbocharged car), and I think I may have tapped the wrong vacuum line. Out on my test drive post-install I idled at -20 psi, spiked around 4 psi, and would cruise around -20 psi. Anytime I applied throttle I would hit 0 but return to -20 at steady throttle. I still have a filter to install but I don't think that's causing this issue. Is the location I tapped a bad call because of the two one way valves up-line? I always see people tap the FpR but due to fitting availability locally I had to tap the line next to it. It is a mechanical Bosch boost gauge. The brass T in the picture is where I tapped.
 

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Gustav
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Looks like you tapped the right line any of the vacuum lines from the intake work.
Your boost sounds right for a stock 1.8T 150hp 20" of mercury at idle is great no vacuum leak and 4-6 psi on boost is standard for a K03 turbo
The Turbo S with 180hp and a K03s turbo boost 9-11 psi stock. If you chose to get a stage 1 tune you will see 10-15 psi. I have a upgraded turbo on my Turbo S and a stage 2+ tune my boost is 23-28 psi.
 

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Discussion Starter · #3 ·
Thank you for your reply. So "Mercury" constitues ant value under zero on a boost gauge? Also, I was pretty sure I have a K03s (irrelevant to host numbers in this instance) is that true? It is an AWV block (2003)? I was under the assumption that without a chip I should spoke at ~13-15 psi and hold at ~8, or is that only with the 180 hp Turbo S trim? I have a side question relating to compression ratios in regards to boost; assuming (to make things simple) my block was rated at 9:5 c.r. If I boost at 5 psi, would that raise my compression to 10? I know this sounds stupid and is unrelated but it just popped into my head so I thought I'd ask.
 

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5/23/10 <3
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The 150hp motors (which you have) should hold 7-8 psi Its 11 psi for the 180hp motors. So something seems slightly off if you're spiking at 4 psi.
 

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Discussion Starter · #5 ·
I will double check my numbers today but I think I am now spiking around 10 and holding around 4-6 but I will update this evening. If I am boosting low could this be attributed to a vacuum loss?
 

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Gustav
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I will double check my numbers today but I think I am now spiking around 10 and holding around 4-6 but I will update this evening. If I am boosting low could this be attributed to a vacuum loss?
Your K03S on a 03 Beetle Turbo is in spec your peak would be 8-10 and your hold would be 4-6
If you are pulling 20" of mercury you do not have a vacuum leak. A boost leak would cause eratic swings on the gauge under load you would also notice the car surging and loose power under load.
 

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Gustav
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349 Posts
I have a side question relating to compression ratios in regards to boost; assuming (to make things simple) my block was rated at 9:5 c.r. If I boost at 5 psi, would that raise my compression to 10? I know this sounds stupid and is unrelated but it just popped into my head so I thought I'd ask.
Here you go this should help.
https://www.rbracing-rsr.com/compression.htm
Your Rods Springs and Valves are the weak link in your engine.
The 1.8L block is good for 1000hp when built properly.
Your factory rods and head components are only good to about 300hp.
 
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