I'm having a problem with boost taper. Starts out at 20 and tapers to 17 using a Buschur MBC and a stage 3 with the Buschur Flash. Car is an 05. The MBC lines are as follows

Input is T'd into the BOV line
Output goes to the wastegate

Here is the dyno plot
https://www.evolutionm.net/forums/at...chmentid=58738

 

thought the flash takes out the boost taper? guess not. doesn't look like your boosting real high to get out of the efficiency of the turbo so that's what it's gotta be, ecu taper still in.

 

Simple, turbo is too small. Happens. You can tighten the wastegate spring but then that would be the lowest boost setting you can have, may also get bigger spikes. You can also go for a larger 10.5 CM housing to allow more exhaust and it should hold higher boost. Gte a full trubo back exhaust, no cat.

 

The stock turbo generally tapers 1-2 psi by redline. Do you stlil have the stock BOV?

 

Hey guys Buschur stage 3=

full TBE no cat
264 cams
FMIC
Intercooler pipes with 1g bov crushed
255 fuel pump
Buschur MBC set to 20 PSi
05 has 10.5 hot side
Has been pressure tested

 

the boost taper is not caused by the exhaust side but the compressor side. the compressor wheel can no longer flow 20psi after a given rpm because the blades are actually getting in the way of the air. bascially the wheel can't move any faster and the air IS moving faster hence causing this type of air back up and boost drop.

if the exhaust side couldn't keep up what would happen is you'd get slowly decreasing boost and a bigger hp drop because the air is getting backed up too badly and it's robbing power.

having cams is gonna make it worse btw... cuz you're flowing more air that the turbo can't keep up with.

 

put a small pill in your OUT line to your wastegate, then readjust your boost controller. should hold more to redline like that.

 

I would contact Buschur about this, if you haven't already.

 

edit...

 

hmmm i thot the boost pill helped the taper...