Boost dropping at the top of 3rd

[1952ray]

WOT in first and second boost holds between 25.5 to 26 psi. A/F hold's at 11.1. At the top of third boost has drop to 22.1 A/F is 10.9 at 5250 rpm's. Per the PL the boost slowly drops. Timing is 20* thru the whole run. 93/alky 42.5 inj. Eric's 5.7 chip. TA49 RJC fm 62mm tb Husek 9.5 3021 TC 2800-3000 stall. I have no knock. Car runs well. Would like to hear theories as to why the boost would drop. Also there are NO leaks, vacuum, headers or otherwise

 

[bison]

Measure the exhaust pressure. Rpm goes up and mass flow goes up. More exhaust pressure to push the wastegate open. Also could be out of compressor or compressor restricted by the compressor cover or a mismatch of wheels.

 

[1952ray]

Measure the exhaust pressure. Rpm goes up and mass flow goes up. More exhaust pressure to push the wastegate open. Also could be out of compressor or compressor restricted by the compressor cover or a mismatch of wheels.

Thank you for your reply. Maybe it's time for a new turbo.

 

[bison]

Thank you for your reply. Maybe it's time for a new turbo.

Maybe but throwing parts at it might not be the answer. Maybe you should check the wastegate tension and bypass hole size first.

 

[1952ray]

Maybe but throwing parts at it might not be the answer. Maybe you should check the wastegate tension and bypass hole size first.

Yes, I do plan to do that. The hole HAS not been open up. I do have a heavy spring in the wastegate. Everything that has been done to this car I have done myself, and Im far from being a guru. Is shipping the car to you a option?

 

[bison]

Yes, I do plan to do that. The hole HAS not been open up. I do have a heavy spring in the wastegate. Everything that has been done to this car I have done myself, and Im far from being a guru. Is shipping the car to you a option?

What down pipe is being used? Has the sealing of the puck been verified? I would expect boost in the mid to high 20's and fairly steady up to 5200 rpm with a TA49. Shipping a car to me is an option. The best thing to do is let the transporters fight it out. You will get the best rate and since your car runs it will be much less expensive. Zip code is 06051

 

[1952ray]

Thanks, I will PM you tomorrow AM