Tuning Out Boost Surge

[LBZ]

Anyone have experience in tuning a vgt turbo for surge issues?

I have a Danville BMW 3794 Stage 2 65mm that I'm having issues controlling the boost. Anything over 12psi it surges up and down and then will level out somewhat. But the higher the boost, the worse it gets and the longer it takes to even out-if it even does at all.

Tried changing vane and boost tables around with poor results so I have a feeling there is more too it. Never ran into this issue with my stocker or my S464 so I'm kind of at a loss.

Anyone got any ideas or able to help me out here?

 

[IOWA LLY]

Mark is awesome when it comes to tuning these things! I would give him a call. He gave me several tips on how to better tune the vgt side of things and his advice was spot on!

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[meshanic]

Have you tried setting the vane tables to resemble the stock LLY vane tables? That has been a good starting point for tuning the 3794. Also make sure the max & minimum vane position tables aren't set to contradict the desired vane position tables. I have not experienced any surge with the 3794 so this does sound very odd to me.

 

[LBZ]

Ok I'll run through the vane tables again when I get home and see how they look. Haven't looked at an lly tune in about 8 years so I'll check it out.

I sent Mark a pm as I don't have his email but no reply and everytime I call he's busy. When I emailed Danville a couple times I got pretty beat around the bush responses and no help so not beating that dead horse anymore.

 

[Dozerboy]

How are you controlling boost? Are you using the vane tables to make boost or are you requesting a boost psi and letting the ECM adjust the vane %.


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[LBZ]

At this point I've left the vane tables as they were and just upped boost. I feel the vane tables may be the source of my issue though. I just don't know enough about tuning the vanes so I haven't started playing with them much. Never had issues with my stocker which has been gone for 6 years now as has most of my tuning remembry. I don't remember it being so tough.

I did have to play with the maf back then also but I haven't touched that since I got things back on the road. It may need a bit of a tweak also.

 

[PureHybrid]

At what rpm are you having trouble? I could see it surging if you're requesting too much boost without enough airflow. What happens on stock boost and vane tables?

 

[LBZ]

Same thing.
Pretty much any rpm above 1500 and over 10-12 lbs.
I'll log it tonight

 

[Dozerboy]

I think you need to work on your vane table. What I did was make a long log of me accelerating at different rates and some cruising at different speeds. Then I map out using efi what percentage of your vanes were usually at in what Cells. You can use that information to create you a new vane table that more accurately reflects the vane percent you need to be running in each cell.

Or just switch over to solely using the vane table. Anyways I think that's what a lot of guys do when running modded vvts. Something about the ECM can't do it because your making to much boost for the sensor. I still use the boost table but I'm only at 35psi and it acts a little screwy.


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[Dozerboy]

Same thing.
Pretty much any rpm above 1500 and over 10-12 lbs.
I'll log it tonight

The boost comes on real strong at or above 1500 for me too. Mine isn't surging on the gauge, but you can damn sure feel it.


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[LBZ]

Mine is clearly visible on the gauge. 5-7psi.

 

[LBZ]

Got a couple logs but can't get on the Internet with my laptop right now so I'll try and do it at work.

Vane position is all over the map when it does it and desired boost stays steady as does throttle, mm3, timing from what I can tell.

 

[NC-smokinlmm]

Is the desired vane postion moving with actual?

 

[LBZ]

I didn't log desired.
I'll giv'r another go tonight.

 

[Harbin_22]

Definitely talk to mark, but you have to mess with minimum and Maximum vane tables

 

[NC-smokinlmm]

Definitely talk to mark, but you have to mess with minimum and Maximum vane tables

Yep, you basically set them up only using about 70% of the range...