My Big28 hates me

[ImolaFem]

I've been battling my 2G for a month now since its come back up.....my Big
28 will not hold boost at 22 psi.

Basically, the Big 28 will hit 22 psi at maximum, then fall off to about
16-18 by the shift. I've gone as far as to disconnect the boost control
from the wastegate to see if it held boost without opening the
wastegate....no avail. So yesterday I took some wire and tied the wastegate
shut to see if it'll hold boost.....still the same behavior. The system has
been pressure tested to 22 psi and held it fine. I talked to the guys at
Forced Performance a few weeks back and they believed it was the wga --
spring too soft where the wg blows open, but obviously its not because I've
taken that out of the equation.

Other comments I've heard is it could be the BOV (but its not cuz I saw that
pressure tested to 22 psi) or the cams. Something about the cams can't
handle the cfm I'm pushing?

Related mods:

Big Greddy FMIC w/ piping
RRE Lower IC pipe
RRE Upper IC pipe w/ 1g bov
RRE TB elbow replacement pipe
Stock 2g TB
Big 28
Ported exhaust mani
Ported o2 housing
buschur 2.5 dp
2.5 test pipe
Thermal 3 inch cat-back

The other odd thing is before I had a Big 16g on this car.....without the
FMIC setup (stock smic). And it held 18 psi all day long. It wouldn't even
fall below 18 psi due to boost creep....

Any ideas?

Mandy

[XakEp]

That is SO your turbo... get a 16G or bigger..

[Hal]

Remember, boost measures the LACK of air flow through the motor.

Everything you do to improve flow (cams, exhaust, etc) or cool the intake charge makes the turbo work harder to maintain the same boost level because at a given rpm point you are flowing more air.

Also, the filter and intake pipe effect air flow INTO the turbo.

If it's too small, you get a pressure drop going in.

Hal

[hoffman]

the stock intake hose was pulled out and replaced with an Injen 2.5" pipe.

now is it possible that part of the problem could be the internal WG. it still uses the T-25 exhaust housing and WG, on a big 16 compressor wheel. so now there is more gas passing through the exhaust mani. to spool the larger wheel. but the opening is too small to maintain the flow, so it will only allow the max amount of gas to pass through, which is enough to maintain 16-18psi. so is it possible that a Tial 35mm WG might help in this case.

i have also been trying to figure out what effects altitude might have on this setup. because of the thinner air, how much help could cams provide the set up? could it be a leak some where in the head gasket? dirty air filter? there is something keeping this thing from holding boost.


but atleast your lights work
:p

[Hal]

Originally posted by hoffmangsx
the stock intake hose was pulled out and replaced with an Injen 2.5" pipe.

now is it possible that part of the problem could be the internal WG. it still uses the T-25 exhaust housing and WG, on a big 16 compressor wheel. so now there is more gas passing through the exhaust mani. to spool the larger wheel. but the opening is too small to maintain the flow, so it will only allow the max amount of gas to pass through, which is enough to maintain 16-18psi. so is it possible that a Tial 35mm WG might help in this case.

i have also been trying to figure out what effects altitude might have on this setup. because of the thinner air, how much help could cams provide the set up? could it be a leak in the head gsaket?


but atleast your lights work
:p

I'm not a big fan of the Injen pipe. If you measure it, it's not all that much bigger than the stock snorkle hose.

Changing the wastegate won't alter the amount of "bypassed" flow (with the gate closed).

Altitude WILL have an effect on spool up, but unless the turbo is "maxed out", it will eventually spool to max boost and hold it.

If there was an air leak, it would be visible by using a logger to examine fuel trims at cruise. If the trims are near zero... no leak.

Adding cams will only make the problem worse. They will increase air flow, which makes it harder for the turbo to make "boost".

Since Mandy has a DSMLink, I suggest she do a log of a run and post it to the DSMLink group. I would like to see the airflow volume and fuel trims.



Hal

[hoffman]

ok, i got it now.

the car is running rich. thin cloud of black smoke everytime the throttle is depressed. so part of the problem would be the tuning. if the fuel trims are set properly, then that would effect the air flow, right? or is it used to see if there is a problem with airflow?

the last time it was logged she noticed high water temps, and the other day we had to add about 1/2gln of anti-freeze/water wetter/water to the radiator. but there are no visible leaks. blown head gasket?

[Hal]

High trims would indicate a leak.

Consistently having to add water after "boosting" and then letting the car cool is indicative of a coolant leak.

Head gasket, water pump "weep hole", hoses, clamps, gaskets... all need to be checked.

Hal

[john]

When the wastegate was wired shut, did you use the flapper arm or did you wire the actuator? I know, I know, but I gotta ask.

[hoffman]

the flapper arm. wrapped twice around the arm(where it joints to the actuator arm), then up to the water pipe and wrapped it twice there.

hehe, tried it with zip-ties the first time:rolleyes: . what was i thinking.