New exhaust, now overboost

[minimoparking]

Just had my 3" exhaust put on.

stock downpipe, No cat, small 3" glass-pack, side-exit.

Now, in gears 1-3, past 5000 RPM, it spikes past 15psi, and hits overboost cut-off.

It seems that the wastegate isn't actuating fast enough. Am I correct in assuming this? What can be done to correct it?

I'm really concerned about this, I don't want to mess anything up. I am also planning a trip to the strip next month, and I'm pretty sure the overboost cutoff will ruin my 1/4 mile time.

[tryingbe]

Type of car, type of engine, type of turbo, etc, don't really matter, am I right?

[minimoparking]

89 Daytona 2.2 TII Stock Garrett turbo

[detobias]

I have a similar setup, and having a similar problem with my 3" exh

try running the wastegate line direct to manifold source which *should* give you minimum boost

then test (may need a long straightaway to pull at least thru 3rd); you may find your boost is creeping up past 15 since the stock wastegate hole cant bypass enough gas, even fully open

well thats what I'm dealing with at least; let us know what you find.

[tryingbe]

Are you using a G-valve or stock boost contorl?

[fastglh86]

The reason you are getting boost cut is because you freed up youe exhaust i did the same thing pretty much and gain 2psi and also hit boost cut.i think thedodgegarage had something on this subject.you can put a boost controler on there or diode on there or 803 injectors just my two cents

[minimopar]

The wastegate control tables in the cal are not prepared to handle the rather responsive turbo you now have. Switching to a grainger-type boost controller should reolve the issue.

[detobias]

if he's dealing with boost creep (not spiking) then a grainger or any other MBC won't fix that,,

if creep, either need to port out the wastegate hole in the compressor housing (to allow maintaining a set low boost) or run a zener (or other MAP cutout) and add fuel to deal with the extra boost and let it creep

if he's experiencing spiking not creep, and running stock solenoid & vacuum lines, then a MBC like the grainger should help

I still suggest running wastegate direct to manifold and see if problems goes away or persists, that will deteermine if its spiking or creep

[minimopar]

A stock Garrett should not be prone to boost creep with his setup, at least in my experience. A Mitsu will definitly creep with a 3" exhaust.

[minimoparking]

Just checked it out. It mentions the MAP diode to keep it from cutting off, but doesn't explain what kind of diode, nor how to do it... anyone?

God, I feel like such a n00b.

been wrenching on cars for a few years now, but this is my first turbo. It's like a totally different animal!

[minimoparking]

Quote:

Originally Posted by detobias if he's dealing with boost creep (not spiking) then a grainger or any other MBC won't fix that... ...if he's experiencing spiking not creep, and running stock solenoid & vacuum lines, then a MBC like the grainger should help...

Both, it seems to spike past 15psi in lower gears, but creeps in 4th & 5th up to 15, and occasionally drops back to normal, or slowly climbs past 15 and cuts-off.

[minimoparking]

Quote:

Originally Posted by tryingbe Are you using a G-valve or stock boost contorl?

stock boost control

[minimopar]

As suggested, try connecting the wastegate right to the manifold. If you still get overboost, then you have a creep issue.

[detobias]

sounds very similar to my problems.. and our setup is similar.

even though Garretts *aren't supposed* to boost creep, I think if you have a free flowing exhaust and other flow improving mods, at some point you will exceed the capacity of the stock WG hole.

my next step may be to wire my WG open completely bypassing the actuator & rod; if I *still* have creep then everything in the system has been ruled out except the WG hole

zener is a special diode that goes on your MAP signal wire to ground, and when the signal V exceeds the rated zener voltage (typically 4.3 or 4.7 volts) the excess V gets dumped to ground so signal V will never exceed the zener V

HTH - more on this subject at thedodgegarage IIRC

[scott_s]

Did you try to hook up the wastegate direct to a vacuum source? (TB Nipple) that should keep you at ~7psi as already stated. If it climbs you need to enlarge the wastegate hole or go .63 exhaust. Be happy you are flowing more now.

My boost went from 12psi to ~18psi with the 3" exhaust. I had some creep with the stock TII turbo after that. That is until my recent head change. Now it will creep bad from 7psi to 16psi pretty quick (direct hook up).