Exhaust bottleneck can cause both slow spool and creep?

[Barracuda]

Hi,

In the current setup (exhaust) I have a evo3 exhaust manifold, BEP 50 trim turbo, Megan Racing o2 housing and custom 3" exhaust starting from downpipe. I've set my boost to 15psi that creeps ~22psi by redline. There's a slight hint of a boost lag too... (15psi after 4000rpm, I've read that these turbos get full boost before 4000rpm?)

Now the exhaust isn't full 3" for the time when I welded it, I had a stock turbo and stock o2 housing. The stock o2 housing has approx 2.2" outlet so I bought a matching flange for it. Now the current o2 housing has a 2.5" outlet diameter while the DP flange is 2.2" making (perhaps?) nice restriction and turbulance. Not to mention the lost power.

The question however is, can that sudden restriction in gas flow cause slow spool and boost creep? Notice that the flanges mate right after the point where exhaust gas coming from the wastegate flapper meets the main gas flow.

 

[LiquidX]

To be honest, most o2 housings are 2.5" at the outlet so that's pretty normal. You can find 3" o2 housings but you'll have better luck and cheaper to make one.

The 3" exhaust is a much more free flowing exhaust than the stock system and will cause some turbos to creep because of that. The 16g turbo is notorious for that. There is much less back pressure going up through the turbine and forcing the exhaust to go out the internal wastegate so you get creep.

I can't give you any info on the 50trim but I'm sure if you went to an external setup you would eliminate the boost creep issue. Wether you go manifold mounted or off of the o2 housing (will need to port the wastegate outlet on the turbine housing) it will deffinatly help your boost creep issue.

 

[kenamond]

Exhaust bottlenecks will suppress creep, not cause it, unless the bottleneck is in the wastegate. That's why folks run into it right after they upgrade to a larger exhaust. Bottlenecks increase the backpressure which makes the WG work better.