The Good, The Bad, and The UGLY

stripSHO

Tyler Durden
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Does a boost leak really care who tunes the car?
Yeah, actually it does care.

Ignition timing matters. Better timing extracts more useful work from the combustion process, which then results in lower EGTs and less turbine energy.

AFR matters. Further away from stoich = cooler EGTs = less turbine energy. This one is likely splitting hairs, but every little bit matters for you folks with the GH interchokers.

Most importantly, cam timing matters. I could tune your car such that it could hold >20 psi all the way to redline with stock turbos. You would not be impressed with the performance. Boost is just a measure of restriction. Bad cam timing = bad engine breathing = great big numbers on your boost gauge to brag to your friends about. Good cam timing = good engine breathing = better performance. Good cam timing usually also raises the dynamic compression ratio, which then extracts more useful work from the fuel air charge, which then leaves less waste energy available in the exhaust to drive the turbines. Good cam timing can also lower combustion temperature, allowing for more timing, which again means less turbine energy to make your turbo go whoosh. Most likely, if you are used to seeing 17 psi boost with Tuner A, but then with Tuner B's calibration your turbos can't make it, it might be because Tuner A doesn't comprehend cam timing. Compare logs yourself and see if there's a difference in cam positions. I've seen as little as 2.5 degrees in the wrong direction add a full psi of restriction at the same given airflow.

Leak or no leak, these are all very valid reasons why a boost "problem" may be apparent with one tune and not the other. But one thing I'll also add is that fuel trims are not a valid measurement for determining a boost leak.
 

SHOthyme

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Most likely, if you are used to seeing 17 psi boost with Tuner A, but then with Tuner B's calibration your turbos can't make it, it might be because Tuner A doesn't comprehend cam timing. Compare logs yourself and see if there's a difference in cam positions. I've seen as little as 2.5 degrees in the wrong direction add a full psi of restriction at the same given airflow.

Please help me understand this part, it sounds like you are stating that even if tuner A can keep more boost, they still might be causing a psi restriction with cam timing?

Am I reading that wrong, cam timing issues can lead to more psi?

Or are you saying if tuner A can keep 17psi and tuner B it tapers to 14psi, it might be because tuner B has cam timing issues?
 

SilvererSHO

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Please help me understand this part, it sounds like you are stating that even if tuner A can keep more boost, they still might be causing a psi restriction with cam timing?

Am I reading that wrong, cam timing issues can lead to more psi?

Or are you saying if tuner A can keep 17psi and tuner B it tapers to 14psi, it might be because tuner B has cam timing issues?


Or are you saying if tuner A can keep 17psi and tuner B it tapers to 14psi, it might be because tuner B has cam timing issues?

He's saying the opposite. Boost is restriction to flow.

Gale Banks explains it nicely.

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FiveLeeter918

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Yeah, actually it does care.

Ignition timing matters. Better timing extracts more useful work from the combustion process, which then results in lower EGTs and less turbine energy.

AFR matters. Further away from stoich = cooler EGTs = less turbine energy. This one is likely splitting hairs, but every little bit matters for you folks with the GH interchokers.

Most importantly, cam timing matters. I could tune your car such that it could hold >20 psi all the way to redline with stock turbos. You would not be impressed with the performance. Boost is just a measure of restriction. Bad cam timing = bad engine breathing = great big numbers on your boost gauge to brag to your friends about. Good cam timing = good engine breathing = better performance. Good cam timing usually also raises the dynamic compression ratio, which then extracts more useful work from the fuel air charge, which then leaves less waste energy available in the exhaust to drive the turbines. Good cam timing can also lower combustion temperature, allowing for more timing, which again means less turbine energy to make your turbo go whoosh. Most likely, if you are used to seeing 17 psi boost with Tuner A, but then with Tuner B's calibration your turbos can't make it, it might be because Tuner A doesn't comprehend cam timing. Compare logs yourself and see if there's a difference in cam positions. I've seen as little as 2.5 degrees in the wrong direction add a full psi of restriction at the same given airflow.

Leak or no leak, these are all very valid reasons why a boost "problem" may be apparent with one tune and not the other. But one thing I'll also add is that fuel trims are not a valid measurement for determining a boost leak.

Fuel trims can determine at what point in the system the leak is present, but having 67% wgdc on logs a month ago and new logs having sky high LTFTs and 95+% wgdc are a good indicator of a leak or other mechanical issue that needs to be addressed, especially with no tune changes in that time frame :)
 

stripSHO

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Fuel trims can determine at what point in the system the leak is present, but having 67% wgdc on logs a month ago and new logs having sky high LTFTs and 95+% wgdc are a good indicator of a leak or other mechanical issue that needs to be addressed, especially with no tune changes in that time frame :)
With a MAF based system, sure. But I'm speaking specifically about this platform, and with speed density I say no way in ****. Besides, hypothetically if it LTFT could show you a boost leak you would expect very low (negative) fuel trims. To me, really high trims can only point to a fueling issue or a sensor failure. High wgdc supports sensor failure too.

Actually... in the case of both those issues coinciding with a tuner brand change, I would most likely suspect a tune file with a 2.5 bar MAP calibration getting sent to a customer who has a 3 bar installed. Which would immediately add 20% to your fuel trims, drop measured boost by 6 psi, send the wgdc into orbit, and probably also explain every other aspect of the car screaming bloo dy mur der as has been described above. Something to double check, for sure. Esp. since you guys default to 2.5 bar sensors with your packages.
 
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SHOthyme

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With a MAF based system, sure. But I'm speaking specifically about this platform, and with speed density I say no way in ****. Besides, hypothetically if it LTFT could show you a boost leak you would expect very low (negative) fuel trims. To me, really high trims can only point to a fueling issue or a sensor failure. High wgdc supports sensor failure too.

Actually... in the case of both those issues coinciding with a tuner brand change, I would most likely suspect a tune file with a 2.5 bar MAP calibration getting sent to a customer who has a 3 bar installed. Which would immediately add 20% to your fuel trims, drop measured boost by 6 psi, send the wgdc into orbit, and probably also explain every other aspect of the car screaming ****** ****** as has been described above. Something to double check, for sure. Esp. since you guys default to 2.5 bar sensors with your packages.

Huh, I didn't even know that would matter, I do in fact have a 3 bar installed.
 

stripSHO

Tyler Durden
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Please help me understand this part, it sounds like you are stating that even if tuner A can keep more boost, they still might be causing a psi restriction with cam timing?

Am I reading that wrong, cam timing issues can lead to more psi?

Or are you saying if tuner A can keep 17psi and tuner B it tapers to 14psi, it might be because tuner B has cam timing issues?
I don't know that I would necessarily label it as timing issues, just not optimal for performance. I think the majority of tuners leave cam timing alone, or very near to stock. All the factory cared about when they determined their valve timing was lowering emissions and not what produced the best breathing engine. But the reality is that across a very wide range of cam advance you will get nearly identical airflows on this engine. The only difference is whether you get it at just 15 psi or have to rev the turbski's up to 20 psi, which affects your wgdc and thus exhaust restriction, therefore impacting mechanical pumping power losses.
 

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