Lower RPM surging/fluttering when light accelerating on highway

[Brett Haviland]

 I'm getting compressor surge ( I think) on the highway in 4th and 5th gears on light accel/boosting.  happens around 10+ psi. turbo starts making boost around 2500 rpm and I can hit full boost (25psi) at around 3800-4000rpm

Have my 1ga
100% stock internal 6 bolt(stock cams)
Evo 3 16G knock off
650cc FIC
Stock BCS with restrictor removed.  .025 restrictor on Wastegate feed line
Walbro 255hp
Crushed 1g bov
meth injection
fmic
3" turboback exhaust
intake
Tunerpro running Swede Density

 Didn't have this problem when I was on wastegate pressure.  Now running EBC with SwD EBC map.  RPM/BOOST target map adjusted, seemed to help.  MAX boost of 25psi.

Thinking that the small exhaust side of the 16g turbine housing is spooling up at the lower RPM on the highway and producing too much boost for the engine to injest.  Once the surge starts, it just gets worse as it boosts higher.  If I do WOT throttle pulls there is no surge at all. Only does it at partial throttle when accelerating on the highway.  And when I was at the track last weekend there was no surge at all when I raced it.

I changed my boost map to run low duty cycle at the RPM/BOOST that the surge happened at.  and it helped.. but now when I floor it at lower RPM's it only hits low boost, 12 psi, then once the RPM reach the higher RPM it boosts up.  loose a lot of power when flooring it in 1st and 2nd gear.

Anyone have any remedy's for this? seems like some setting that limits boost at lower TPS would do the job.  Unfotunalty there doesn't seem to be any setting like that in Swd

I have included a sceen shot of my boost control map

[Brett Haviland]

I think I'm going to ditch the crushed 1g BOV and try a adjustable aftermarket

[KevinBuckham]

If you don't want to lower the overall boost too much the options really are only two: reduce boost production at the engine speed that is causing the problem or increase VE / engine air consumption .

- Larger turbo, turbine wheel or higher A/R exhaust housing would deal with surgeline boost production
- larger engine displacement and/or larger cams can increase air consumption of the motor

Also with electronic control of boost with an RPM boost table you can reduce boost target until higher RPMs.

[Brett Haviland]

Yeah I reduced my duty cycle in those areas and it defiantly helps take care of the compressor surge.  Putting on a greddy style adjustable bov also helped the problem  somewhat as well, now that i have had a couple weeks to drive it.

It sucks not letting the turbo hit boost as quick as it wants tho, you really notice the lag when accelerating from lower RPM in town...  so I adjusted the boost maps back to "agressive" settings.  Car rips much better now...  just have to try and avoid the boost/throttle input range that creates compressor surge.  I think I am going to install my switch selectable boost maps also and then that was i can flick a switch on the dash and that will allow me to change to a low boost setting map, which will eliminate the surge all together.

[Brett Haviland]

Well I figure I'll update this post.   Got it all figured out.  I was able to change my boost map to TPS /RPM based so at the lower tps input (below 60 percent throttle) I have it set so that it's at 0 duty cycle and it won't surge anymore on the highway on partial throttle accelerations.  Then when I go WOT or above 60% throttle I get my normal high boost duty cycle settings.

Worked perfect.  Thanks Lowell for the suggestion!

[Jordan Kruger]

Good to know