Boost Dropping

[noway55]

OK, I am a little new to this, but looking for some suggestions on what to look at.

If I go WOT, I see a boost spike to about 24lbs and then after about 1-1.5 sec it fades back to 18 lbs and hold pretty good.

If I ease into it and hold say 75% throttle, it will get to about 21-22 and hold that level.

What is causing the spike and drop off when WOT?

Right now I am using a Voodoo MBC and have a Greddy Profec b Spec II on order. I am hoping this will fix my issue. Trying to get to 25lbs steady boost.

 

[gusszgs]

Ya, I was having the same sort if issue at less boost values (15 dropping off to about 13).
Was told that the some chips are programmed to reduce boost at WOT 3rd gear.

 

[noway55]

I am full manual on the boost. Using a Vooddoo MBC.

Not using factory boost control. Computer has no control on boost levels

Also, running Code $59 (modified version of $58)

A/F is about 10.5

timing is about 20-22

It just doesnt want to hold the boost up at a higher level.

 

[noway55]

Anyone have any thoughts on this?


What if I were dumping too much Meth? Would that cause my symptom here?

Just an idea.

 

[trev0006]

pressure test the pipes

 

[noway55]

pressure tested the pipes with my HD (home depot) tester. It wont hold 1psi. Air is leaking out around throttle body coupler. I have replaced coupler and new T-Bolts. Need to get rid of this TPI intake somehow and eliminate the oval junction. A band clamp just doesnt like to go around the oval very tight all the way around.

Can you weld to cast aluminum? (throttle body) to the intake pipe which I think is aluminum (not cast).

 

[GNVYUS 1]

I'm surprised you haven't seen threads on this in this section.

Your problem is called boost spike, the solution is to open the turbo's exhaust hole to about 1 1/8" if your down pipe puck is at least 1 3/8". Aftermarket downpipes have larger pucks.

Take off the DP and with a dremel and a shop vac, open up the hole using the carbon ring as your guide with where the puck is seating against the housing. I use the shop vac to suck out the metal debris and make sure you smooth out the inside of the housing to round out the edges.

That should cure the spiking or have no more than 1psi.

The manual controllers are great but this is one side effect if the hole is not large enough to pass the exhaust gases when it pushes the wastegate actuator open.

 

[noway55]

Anyone have a pic of this procedure?

I'm surprised you haven't seen threads on this in this section.


Your problem is called boost spike, the solution is to open the turbo's exhaust hole to about 1 1/8" if your down pipe puck is at least 1 3/8". Aftermarket downpipes have larger pucks.

Take off the DP and with a dremel and a shop vac, open up the hole using the carbon ring as your guide with where the puck is seating against the housing. I use the shop vac to suck out the metal debris and make sure you smooth out the inside of the housing to round out the edges.

That should cure the spiking or have no more than 1psi.

The manual controllers are great but this is one side effect if the hole is not large enough to pass the exhaust gases when it pushes the wastegate actuator open.