Crazy boost creep.

[Spyder]

I recently rebuilt my engine.

Car came with a rebuilt engine that was done horribly. It has a new small 16g running stock waste gate.

Stock cams

3" open exhaust with Magnaflow muffler.

The MBC looks like it was assembled from hardware store parts. It does have a spring and ball assembly inside.

Before I rebuilt the engine, boost would hold fine at about 13 psi.

After build it creeps, the colder the outside temp, the more it creeps.

I have it set initially at about 12 psi it will hold until I get into higher RPM and then it just runs up. Like I said, the colder it is outside, the more creep. It will creep up to about 17 psi but I think it would go higher. I am taking my foot out of it as the car is getting fuel cut out I assume.

The MBC is hooked up to the nipple on the turbo and then into the waste gate. Very short hose route.

Thanks for help.

 

[Barnes]

Bypass the MBC and run a vacuum line straight from the turbo outlet elbow (assuming it has a nipple) straight to the wastegate. If you don't have that nipple, run a line straight from the intake manifold.

That way you can confirm the MBC isn't in anyway the problem.

Also, did you change ANY other parts? Did compression ratio change?

 

[prove_it]

Details on the rebuild will help.

 

[Spyder]

The guy that rebuilt it before I got it put .20 over pistons in. Stock compression.

I re-used the pistons, new rings and honed the cylinders.

Rebuilt head, stock sized valves, new
New Guides, used beehive springs and retainers.
New seals.

stock cams.
ACL bearings.
Cyclone intake instead of stock. Haven't hooked up the canister for the secondary runners yet.

I will try running the vacuum line. Thanks Barnes.

 

[prove_it]

Could be the manifold. It does make a difference in spool and boost characteristics.

 

[coyotes]

have you checked that the wastegate is set up properly? If it is out of adjustment the flapper won't open all the way, creating a restriction which would cause creep.

 

[G]

What o2 housing are you running? Is it ported?

 

[Spyder]

Stock manifold and o2 housing. No porting.

I checked the WG movement manually and it appeared to move freely. That was before I had the engine in the car. And it has been about 4-5 thousand miles since.

 

[BluFalcon]

Does the T/H housing have a larger flapper and a ported wastegate outlet? If its a standard OEM MHI turbine housing, boost creep can be an issue with an unmodifed turbine housing.

 

[Spyder]

I don't believe it is modified. It was working fine before the rebuild so I didn't take it apart.

 

[iceman69510]

Did it do this before it was real cold? Wondering if there is moisture vapor freezing up or something.

 

[Spyder]

when the temps are warm, it doesn't do it.

I have yet to try the vacuum line suggestion Barnes made. I will try that today.

 

[theevozero]

Quoting BluFalcon:
Does the T/H housing have a larger flapper and a ported wastegate outlet? If its a standard OEM MHI turbine housing, boost creep can be an issue with an unmodifed turbine housing.


Gonna have to agree with Ed on this one. I've had the exact same issue. Port the turbine housing in the CORRECT location and creep issues become a thing of the past.

 

[Spyder]

How do you decide what is the CORRECT position?

 

[Barnes]

Just to be 100% clear, what *exactly* changed from the time you didn't have boost creep, to now.

 

[Spyder]

Rebuilt engine:
1) Same Pistons
2) Re-honed cylinders
3) New Rings
4) Cyclone intake instead of stock intake. (Canister not hooked up yet)
5) Aggressive break-in

Weather is much colder.

That is it.

When I removed the turbo, I left the MBC connected and left the O2 housing on. Everything worked before the rebuild so I left it as is.

Could timing being off affect it?

 

[swe_gvr4_1991]

To me it seems you're having less leaking cylinder hones now than you had before and therefore seeing a more aggressive boost pressure ramp.
Ontop of that add the Cyclone manifold with it's design and a unported 16g.

How is the Cyclone vac canister hooked up now, is it just open to the air by the nipple or have you capped it? Is the extra runners fully closed by the vac canister?

 

[Spyder]

I have the vac canister closed off with a nipple. The flaps are held close with the vacuum canister it's self.

 

[Wookalar]

Port that wastegate flapper hole and get a bigger flapper to cover the larger hole. Or go external gate.

My 16g eclipse used to creep like crazy in the cold winter months in chicago, even with a larger o2 housing/dp.

Or it may be possible you have some build up on the exhaust manifold flange mating surface to head, and you need to lay it on a sanding belt or have it milled so the surface is true again. Of course if you had creep that bad due to a exhaust leak you would hear it.

 

[Spyder]

The only leak I have in the exhaust is in the flex pipe. There is a slight leak there. I checked the exhaust mani before I re-installed it. Put new exhaust studs in the head and helicoiled any studs that were loose. Used a multi layer metal gasket. New gasket for turbo to mani connection. new gasket for o2 to down pipe.