Boost peaks at 15psi at 4500rpm and drops to 11psi. Couple of suspected reasons are:
1.) Possible exhaust leaks around cat and possibly where dp mounts to turbo
2.) Some people have told me the Turbo XS boost controller is the reason but Turbo XS says it's
3.)the wastegate on the turbocharger not able to support this amount of boost. Does anyone else have any ideas or had this problem before?

Hahn recommends an electronic boost controller but that's a lot of damn $$$ to throw down just to hold boost at 15psi, and of course they just so happen to sell the same boost controller they recommend.

Setup:

Turbo

- Hahn S16G, Hahn manifold, FMIC, Greddy type-s BOV, stl piping, internal wastegate, Turbo XS standard boost controller, custom 3" downpipe

Fuel

- Walbro 255lph pump, aeromotive 1:1 fpr, Megasquirt (v3 board), 450cc injectors

Ignition

- Crane Fireball ignition box, MSD coil pack, MSD wires, NGK BKR6E-11 plugs

Engine

- Wiseco 8.8:1 pistons, Eagle rods, minor head-work, greddy 2.75" catback exhaust

Originally posted by evotunedscc
the wastegate on the turbocharger not able to support this amount of boost.

I don't see why it would be the wastegate, usually the problem that arises with an internally gated turbo at higher boost is that the wastegate can't flow enough air and you get boost creep not a drop in boost.

edit: I suppose it could be the wastegate if it's getting stuck open after it opens when you initially hit peak boost

Double check all your vac lines and do a boost leak test and you may be able to find the problem, you may have a small leak that shows up once you go over 11-12 psi but you still hit peak boost while the turbo is spooling, once the wastegate opens and the turbo stops spinning faster it may leak down to that 11-12 psi from 15.

Definetly check out those exhaust leaks too though and if you can find someone else with a mbc just swap them out real quick to see if that's your problem.

Originally posted by cs82685
usually the problem that arises with an internally gated turbo at higher boost is that the wastegate can't flow enough air and you get boost creep not a drop in boost.

It's actually the other way around. A too small waste gate can't flow enough exhaust at low boost, and causes you to get boost creep.

you have the wrong spark plugs for this application. imo.

EDIT: Unless you gapped them down from .045 to .028ish but then thats still not good.

I know, I will get some BKR7s in a few days or BKR8IX are two ranges colder... might get them but someone told me not to use iridium plugs in my car so I gotta do some more research on that.

don't even research.

don't use iridium plugs.

NGK bkr7e

no -11 or anything like that. that means they are gapped at 1.1mm or 0.045"

My turbo XS dual stage held rock solid at 23 psi all day long back in the day. You could always borrow someones MBC for the 5 minutes it would take to troubleshoot the issue. Its a quick way to rule it out.

My bet is on boost leaks. If your car was set to 11 psi then creeping up to 15psi it would make more sense but a 16g has absolutely no issues maintaining 15psi all day long.