Weird boost drop

[moses]

Sorry if this has been talked about before but i searched and couldn't find any answers on whats happening to my car other than do a boost leak test which i have done and found no leaks.. i've got new gaskets all around, new vacume lines, and there is no drop on the tester...
Normal driving it runs great no problems spools to 15psi and stays there,even getting on it nothing but as soon as i go WOT it hits 15psi(what my mbc is set to) then slowly drop to 12psi and then hit what feels like fuel cut. I also tried dropping to 13psi and it does the same thing.
My car and mods are...
91 gsx with great compression across the boards and a rebuilt head all stock internals...
Open maf with k&n, hard intake, crushed stock bov still recirculating, rebuilt and ported 14b ,MBC, ported exhaust mani with no cracks and good gaskets, 3in turbo back with high flow cat, emision removal, warbro 190.
Any suggestions will help greatly,
Thanks in advance

 

[talontd92tsi]

Did you do your boost leak test with your throttle body open or closed? Maybe its an intake gasket.

 

[oldman]

Did you do your boost leak test with your throttle body open or closed? Maybe its an intake gasket.

Having the throttle plate closed will not stop pressure from entering the intake manifold area.

OP, what were the details of your leak testing procedures and results?

 

[moses]

Its got a new intake, throttle body, and the elbow gasket. I plugged the pipe at the j pipe and put my tester on the pipe that goes to the tb, ran it up to 20psi and held it there for about 20 minutes and the pressure didnt drop at all.

 

[oldman]

Its got a new intake, throttle body, and the elbow gasket. I plugged the pipe at the j pipe and put my tester on the pipe that goes to the tb, ran it up to 20psi and held it there for about 20 minutes and the pressure didnt drop at all.

So basically you did half of a boost leak test, the easier half no less.

 

[moses]

Well ive done a cylinder leak down test too an it held its own too, i dont know how to test the intake other than taking out the cam to close the valves.

On the other hand any thing below 10psi is runs great with out any problems...feels like it pulls harder in the higher rpms too.

 

[turbosax2]

Well ive done a cylinder leak down test too an it held its own too, i dont know how to test the intake other than taking out the cam to close the valves.

On the other hand any thing below 10psi is runs great with out any problems...feels like it pulls harder in the higher rpms too.

You need to do a proper boost leak test. Put the tester on the turbo and test to 20 psi. See how long it holds that pressure.

 

[oldman]

Well ive done a cylinder leak down test too an it held its own too, i dont know how to test the intake other than taking out the cam to close the valves.

1. What does a leakdown test have to do with the subject at hand?

2. Only one set of intake valves will be opened during a static intake pressure test and unless you're at valve oeverlap (reason why you're suppose to put the engine at 30* ATDC to avoid valve overlap), the cylinder with the open intake valves should hold pressure because the exhaust valves will be closed.