K04+ untunable via Trifecta?
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From: 6000ft on a Mountain in Colorado!
K04+ untunable via Trifecta?
Hey guys,
I've been working with Vince on my K04+ for a very long time now. It's been over a month now I'm certain.
Anyway I've been experiencing KR and Surge/Flutter when I floor it in 3rd and 4th below 3000 RPMs. Generally happens when I reach close to full boost. Now from what I understand the flutter/surge may be normal, you guys may elaborate if it is true. But the KR isn't.
I threw my stock ECU on (spare ecu with stock tune) to see if this happens during the same conditions. Unfortunately there was a lot of traffic during this test and from what I experienced the issue was completely gone. I'm gonna verify these results tomorrow on my way to work.
Here's Vinces latest reply
Now the depressing part for me... 
During my log today as per request, all went fine so I thought. Then when I was driving home I noticed a whining noise coming from my car. It's most noticeable in 1st, less in second, can barely be heard in third and 4 and 5 can't be heard. This is either because of the wind or or road noise or exhaust or all the above.
The whine seems to follow the turbo, -10 in vacuum on the boost gauge and doesn't stop whining until I shift, then it whines down in the same sequence as my bypass, blows off. This noise is not as loud as some of the youtube videos I've seen, but it's definitely noticeable in the first 2 gears.
Whats your take in this CSS.net?
I've been working with Vince on my K04+ for a very long time now. It's been over a month now I'm certain.
Anyway I've been experiencing KR and Surge/Flutter when I floor it in 3rd and 4th below 3000 RPMs. Generally happens when I reach close to full boost. Now from what I understand the flutter/surge may be normal, you guys may elaborate if it is true. But the KR isn't.
I threw my stock ECU on (spare ecu with stock tune) to see if this happens during the same conditions. Unfortunately there was a lot of traffic during this test and from what I experienced the issue was completely gone. I'm gonna verify these results tomorrow on my way to work.
Here's Vinces latest reply
The "surge" is happening because of the modified compressor - I'm working on increasing overlap to reduce this, but ultimately we may need to lower desired boost levels in the range where the surge is happening. This doesn't happen on the stock tune because the boost levels are lower there. I'll review the logs tomorrow and see what they show.
During my log today as per request, all went fine so I thought. Then when I was driving home I noticed a whining noise coming from my car. It's most noticeable in 1st, less in second, can barely be heard in third and 4 and 5 can't be heard. This is either because of the wind or or road noise or exhaust or all the above.
The whine seems to follow the turbo, -10 in vacuum on the boost gauge and doesn't stop whining until I shift, then it whines down in the same sequence as my bypass, blows off. This noise is not as loud as some of the youtube videos I've seen, but it's definitely noticeable in the first 2 gears.
Whats your take in this CSS.net?
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From: 6000ft on a Mountain in Colorado!
However, I am the first one he's tuned at 5800ft above sea level and 91 octane, so maybe that's the issue.
Here is the issue....... Have him ramp boost in slowly, and increase boost vs rpm. Instead of one large sum of boost make it linear. you may loose your Tq, but the large boost spike/ quick ramp is causing the issue with fluttering and kr. There is to much load present for the desired Tq, and possibly to lean or to rich..
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From: Rochester, New York
yeah he sold it, he has a cruze now. but he still might have some useful info being that he had a bit of trouble with tuning his k04+ before too. i THINK his prob was that he was trying to run e85 but was running out of fuel up top... not sure tho.
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Can you elaborate on this?
Also I put my stock ecu back in and it drives better than tuned. But going WOT it stops at 14psi then as I increase in speed so does the boost. I got it to about 16psi before letting up. This is a 4th gear WOT mind you. Is this typical behavior? I'm assuming this is learn down because of the bigger air flow due to Turbo and SRI
Second gear pulled pretty good but I didn't notice the boost.
One other thing I noticed is I'm not getting KR at low throttle. Vince called this tip in but I didn't experience it on this one drive. I'm gonna leave this tune on for a bit, the only concern I have is its getting up there in LTFTs
Also I put my stock ecu back in and it drives better than tuned. But going WOT it stops at 14psi then as I increase in speed so does the boost. I got it to about 16psi before letting up. This is a 4th gear WOT mind you. Is this typical behavior? I'm assuming this is learn down because of the bigger air flow due to Turbo and SRI
Second gear pulled pretty good but I didn't notice the boost.
One other thing I noticed is I'm not getting KR at low throttle. Vince called this tip in but I didn't experience it on this one drive. I'm gonna leave this tune on for a bit, the only concern I have is its getting up there in LTFTs
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From: Upstate, SC
only read the first post.... pretty sure you're just finding out what it is like to have a big compressor on a small turbine... you've hit the surge line... ported shrouds fix this and is the reason Forced Performance uses their HTA86 cover on their stock frame turbos.
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From: Kathmandu
I hope the whine your hearing isn't the turbine wheel making contact with the housing.
Personally, Vahd, I think you should just go back to stock turbo. This thing has been nothing but a pain in the ass for you.
Personally, Vahd, I think you should just go back to stock turbo. This thing has been nothing but a pain in the ass for you.
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only read the first post.... pretty sure you're just finding out what it is like to have a big compressor on a small turbine... you've hit the surge line... ported shrouds fix this and is the reason Forced Performance uses their HTA86 cover on their stock frame turbos.
As for the BNR, I'll read up on how to do the BOV, it's the main reason why I didn't go that route. Maybe with some understanding I'll be less apprehensive this time around.
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From: 6000ft on a Mountain in Colorado!
Just got a update from Vince about the whine and what's going on with my car.
Seems logical
Thanks I'll check it out!
As for the whine, Every turbo car I've owned does that!
If you're curious, here's what's going on...
Because the compressor vs turbine is larger than before, it requires more exhaust flow to keep the air moving forward. At lower RPMs, there's insufficient exhaust flow to prevent the air from backing up into the compressor, which causes compressor surge.
This is especially problematic at high altitude due to overall lower air density.
There's two main ways of dealing with this: increase valve overlap at low to mid RPMs, and decreasing boost. The last four or five tune iterations attempted to deal with it through overlap, because, nobody wants to have to decrease boost levels (pressure ratios), right? LOL. Unfortunately we just weren't getting the results we needed through overlap adjustments alone, so we'll have to dial back the maximum pressure ratio in the low to mid range.
For what it is worth, I had to do this, even at sea level, on my 1.4L turbo tunes because of the compressor vs turbine sizing GM chose on the stock turbo.
As for the whine, Every turbo car I've owned does that!
If you're curious, here's what's going on...
Because the compressor vs turbine is larger than before, it requires more exhaust flow to keep the air moving forward. At lower RPMs, there's insufficient exhaust flow to prevent the air from backing up into the compressor, which causes compressor surge.
This is especially problematic at high altitude due to overall lower air density.
There's two main ways of dealing with this: increase valve overlap at low to mid RPMs, and decreasing boost. The last four or five tune iterations attempted to deal with it through overlap, because, nobody wants to have to decrease boost levels (pressure ratios), right? LOL. Unfortunately we just weren't getting the results we needed through overlap adjustments alone, so we'll have to dial back the maximum pressure ratio in the low to mid range.
For what it is worth, I had to do this, even at sea level, on my 1.4L turbo tunes because of the compressor vs turbine sizing GM chose on the stock turbo.
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From: Bogalusa
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From: Tejas
I echo what Vince said. The K04+ has a very large compressor wheel compared to the turbine wheel size meaning that it can get into conditions where you're basically trying to get the turbo compressor wheel to do too much work when you're giving the turbo's exhaust wheel too little to work with.
That being said, you need to create more exhaust flow past the exhaust wheel of the turbo before you can start really ramping up boost pressure, or you'll get surge. This means more RPM. The surge is probably causing KR due to the disruptions in intake airflow when it's happening. That's why it's not happening in light boost.
I agree with what Chevycobaltss3 stated below, and I believe this will help fix your problem.
That being said, you need to create more exhaust flow past the exhaust wheel of the turbo before you can start really ramping up boost pressure, or you'll get surge. This means more RPM. The surge is probably causing KR due to the disruptions in intake airflow when it's happening. That's why it's not happening in light boost.
I agree with what Chevycobaltss3 stated below, and I believe this will help fix your problem.
Here is the issue....... Have him ramp boost in slowly, and increase boost vs rpm. Instead of one large sum of boost make it linear. you may loose your Tq, but the large boost spike/ quick ramp is causing the issue with fluttering and kr. There is to much load present for the desired Tq, and possibly to lean or to rich..
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From: Tejas
This isn't the stock K04. This is a K04+. The K04+ is a modified K04 with a larger compressor wheel. This means it can move more air than a normal K04, but it also means that the turbo is a bit "imbalanced" as far as the relationship between its compressor and turbine wheel size. The turbine wheel is arguably too small for the larger compressor wheel that its driving.
This isn't the stock K04. This is a K04+. The K04+ is a modified K04 with a larger compressor wheel. This means it can move more air than a normal K04, but it also means that the turbo is a bit "imbalanced" as far as the relationship between its compressor and turbine wheel size.