boost problem

[99gstspyder69]

My 99 gst was on the dyno last night and there seems to be a problem with boost. I have an external tial 38mm wastegate with a 14lbs spring. 1st run 28lbs. It should of been a little over 14lbs. We disconnected the boost control solenoid and ran vacuum the the w/g and still pulling 28 lbs. We removed the w/g entirely and it built 10lbs. The tuner said it was the w/g IN pipe to the manifold is to small. Its 1" he said 1 1/2 it needs to be. Btw this is stock block, 272 cams, and a 7 blade hx35 with stock back housing. The manifold is a punishment racing budget manifold. Please help!

 

[xiteamxi]

My 99 gst was on the dyno last night and there seems to be a problem with boost. I have an external tial 38mm wastegate with a 14lbs spring. 1st run 28lbs. It should of been a little over 14lbs. We disconnected the boost control solenoid and ran vacuum the the w/g and still pulling 28 lbs. We removed the w/g entirely and it built 10lbs. The tuner said it was the w/g IN pipe to the manifold is to small. Its 1" he said 1 1/2 it needs to be. Btw this is stock block, 272 cams, and a 7 blade hx35 with stock back housing. The manifold is a punishment racing budget manifold. Please help!

1" pipe to the wastegate would definitely be a bottle neck, your running an open t3 manifold to a twinscroll hot side?

 

[99gstspyder69]

Thank you, i needed to hear that from someone else.

 

[99gstspyder69]

My tuner wants to chop the pipe, ream the hole and reweld 1 1/2. Does that sound like it could work?

 

[xiteamxi]

Well think of it this way the lower the boost you want the more exhaust has to go around the turbo 38mm=1.496" what's your target boost? I'd assume you would want to be in the 20ish range any way to justify a turbo that size double check the springs anyway.

 

[ATEAV8]

Post up your dyno graph logging boost. If boost hits 14lbs fast but then creeps to 28, id say the exhaust isnt exiting fast enough meaning pipe to WG is to small or bad location where its fed from. If its just hitting 28psi instantly, then id say you have no boost going to the bottom of your wastegate or a ripped diaphram in your wastegate.

Post a picture of dyno graph logging boost and manifold design. Let me know.