No boost control after 3" exhaust

[shackwrrr]

Had a crappy exhaust on the van with 2.5" kink bends and reverse step downs. Well hacked that off and installed a 3" strait pipe with a slight bend to the right and comes out in front of the tire. Now it won't hold boost, it stops at 5psi for a second then starts climbing to over 15psi. Before the exhaust it would hold 5psi rock solid. The vacuum line goes straight from the compressor nipple to the waste gate can.

[cordes]

Mitsu or garret?

[shackwrrr]

sorry, garret with 2.5in swingvalve and big can.

[cordes]

Have you looked at the actuator rod to verify that there isn't any interference with anything? That's an odd problem.

[turbovanman²]

Sounds like the wastegate shitt the bed.

[tryingbe]

Garrett isn't known for boost creep. Try to see if there anything prevent the punk from moving, you can do that by applying compressed air to the wastegate actuator and see if the arm moves.

[shackwrrr]

I will try to actuate it with some compressed air tomorrow, possibly sunday. I have a spare so if it's bad thats not a big problem. I figured that boost creep was pretty unlikely since I have pretty much no performance modifications and the stock 1 piece intake. I just thought it was really weird that it started right after the exhaust swap.

[GLHNSLHT2]

I've had garrett's creep on a 2.2 and a 2.5. The casting for the WG hole is just too small for the exhaust size. My friends minimum boost is 15psi with an ATP SV and 3" exhaust on his Minivan on a stock T2 garrett.

[shackwrrr]

Hit it with some air today and it opens fine. Flap opens fine, actuator moves about 5/8-3/4". I verified the vacuum line and it still goes past 15. Maybe I'll try moving the line from the compressor nipple to the vacuum block.

[wallace]

I had same issue when going to 3" in my 90 mini with a .63 chrysler housing on it you will have to port the wastegate hole or live with it. I think it's all the load from the weight of the van?

[shackwrrr]

I've also noticed that the exhaust note is different from other 2.5's I've driven. It has a cackle to it and its really rough and raspy like a v8 with small pipes. The sound of it bothers me. My shadow had a nice deep growl to it and sounded smooth. The van almost sounds like a Subaru under full throttle. I thought timing but its dead on. Just the nature of the .48? My shadow had the .63.

[85boostbox]

Now when you say timing you mean with a light or cam. Seems to me like your came timing is retarded. That would cause a boost creep.

[shackwrrr]

I am pretty sure cam timing is dead on but I can check again. Ignition timing is good. 12* with cts disconnected. Making me wonder about cam timing. EGTs were pretty high before my Pyro quit working.

[5DIGITS]

....... Now it won't hold boost, it stops at 5psi for a second then starts climbing to over 15psi. Before the exhaust it would hold 5psi rock solid. The vacuum line goes straight from the compressor nipple to the waste gate can.

A few questions..

• Is the WG rod adjustable?
• Which can (87 small 4.4lb spring, 89 Large w/ 2.3lb spring etc...)
• Is the WG port stock or ported?
• Straight pipe with no muffler, correct?
• Hose from compressor to WG can - is this how it's always been run?
• Has the calibration (fuel/timing) been adjusted to compensate for the reduced (nearly non-existent) back pressure?

Thanks

[shackwrrr]

Non adjustable rod
I think its an 89, PO said it came from an 89 Shelby z
Stock hole
Straight pipe yes
No cal changes
Hose now goes from vacuum block to waste gate can

[5DIGITS]

Non adjustable rod
I think its an 89, PO said it came from an 89 Shelby z

Is the can 2 inches in diameter or 3 inches?

• Is the WG port stock or ported?
• Straight pipe with no muffler, correct?
• Hose from compressor to WG can - is this how it's always been run?
• Has the calibration (fuel/timing) been adjusted to compensate for the reduced (nearly non-existent) back pressure?

[shackwrrr]

Is the can 2 inches in diameter or 3 inches?

• Is the WG port stock or ported?
• Straight pipe with no muffler, correct?
• Hose from compressor to WG can - is this how it's always been run?
• Has the calibration (fuel/timing) been adjusted to compensate for the reduced (nearly non-existent) back pressure?

3" diameter. I answered the rest, you caught it before I added them.

[5DIGITS]

3" diameter. I answered the rest, you caught it before I added them.

Thanks

Try this as a better way to test the WG can diaphragm - Apply pressure (10-15psi), shut off the supply but keep it sealed, and check if the can closes. This will certainly contribute to creep, if it's leaking.
A hose from the compressor to the actuator provides more pressure than a hose from the intake. This is due to the pressure drop across the intercooler (the compressor psi is approx 2-3psi higher) - it was helping you, if the actuator is leaking.
The area gained when going from 2.5" to 3" is significant. The increased exhaust flow places a higher demand on the bypass hole and now the flapper valve will need to open farther to make the same boost.
With this said and assuming the actuator diaphragm is OK, you may be beyond the capability of the bypass hole especially if the EGT's have risen significantly, due to a leaner mixture.
Also, when you lower exhaust back pressure there's less need for spark advance. Consider reducing spark - not for the boost but for your engine.

In short, check for a leaking WG diaphragm. If it's OK you may need to consider the next step of opening the bypass hole, reducing spark advance, and increasing fuel flow.
This should get boost control and EGT's back in order.

I hope this helps.

[speedfreek500]

Great post there 5digits, i will remember that.

[shackwrrr]

Thanks

Try this as a better way to test the WG can diaphragm - Apply pressure (10-15psi), shut off the supply but keep it sealed, and check if the can closes. This will certainly contribute to creep, if it's leaking.
A hose from the compressor to the actuator provides more pressure than a hose from the intake. This is due to the pressure drop across the intercooler (the compressor psi is approx 2-3psi higher) - it was helping you, if the actuator is leaking.
The area gained when going from 2.5" to 3" is significant. The increased exhaust flow places a higher demand on the bypass hole and now the flapper valve will need to open farther to make the same boost.
With this said and assuming the actuator diaphragm is OK, you may be beyond the capability of the bypass hole especially if the EGT's have risen significantly, due to a leaner mixture.
Also, when you lower exhaust back pressure there's less need for spark advance. Consider reducing spark - not for the boost but for your engine.

In short, check for a leaking WG diaphragm. If it's OK you may need to consider the next step of opening the bypass hole, reducing spark advance, and increasing fuel flow.
This should get boost control and EGT's back in order.

I hope this helps.

I have to get some fittings and whatnot then I can test its holding abilities. I did check my cam timing and it is dead on according to the torque converter mark. If that is off I don't know. That would throw my ign timing off too.