ok so i was doing some WOT pulls and i could tell something was wrong i boost 28psi then its falls all the way back down to 18-19psi. i did a boost leak test and its all good, i dont know whats going on.

stock turbo and wasgate
272 cams
hardpipe kit
hks intake
3in TB exhaust
deachwerks 880s fuel injectors

please help

 

There's your answer.

What method of boost control are you using?

 

its a grimspeed 3port.

this just started though??? what do you think it is??? it nearly has 100k on it

 

What BOV do you have? I had a similar issue with my stock BOV would taper also had a very small boost leak at my intake.

 

What's your WGDC around 6-7k?

If it was fine before you may have a leak somewhere.

 

I have an hks with recurc kit on it. I boost leak three times and can't find any leak.

 

WGDC? Sry I don't understand what that means I'm sorry.

My boost starts to taper down right at 6k rpm and is at 18psi by 8k and I have been peaking at 28psi

 

It will always be 18-19 at 8k on a stock VIII turbo. WGDC means WasteGate Duty Cycle which is a percentage that tells you how much you are requesting.

For instance 100% means EVERYTHING it can do, think the boost line off. 0% is the least it can do or straight wastegate line.

 

It used to taper off at 23-25 psi. It just started doing this

 

I would replace all vacuum lines first. Next suspicion would be injector seals or throttle body shaft seal. It could also be a leak on the wastegate. Ensure there are no cracks on the hotside of the turbo, particularly where the wastegate is separated from where the o2 housing connects. It could also just be the turbo if you have 100k on the car. Pretty sure stock turbos are not ball bearing. Trying to get the stock turbo to hold that much boost over 8,000 rpm is asking a lot. Even my 35R tapers by about 4psi or so above 8k rpms.

 

Another idea is that it could be clutch slipping. If your clutch slips when you hit peak boost, it may appear that your boost drops off sharply

 

if it doesn't slip at peak torque it shouldn't slip at 6k+, which is the rpm range the OP is talking about.

 

I think your boost gauge just started working correctly. What did the car boost taper to before this problem started?

 

it tapered down to 25 psi before this all started. ill check for cracks tomorrow. and re do some vacuum lines. i just bought a used evo 9 turbo and am getting it sent off for upgrade to MAP for an EF3 upgrade and a new wastegate.

you guys think my stock block can hold that? compression is 150/160/160/160 +or- 2 psi because it is an analog tester.

my goal is 400whp, i read to try adn keep the tq under 400 and i should be fine.. what you guys think? remember the car has over 100k and im making 298whp and 255tq and that was on a mustang dyno. and i cant get e85 at my location.

 

Couldn't find any cracks, replaced vacuum lines and still not fixed. Bought a used evo turbo and a MAP wastegate. I'm hoping it's just and old turbo and wastegate issue. Have any of you tried the spring trick for the wastegate?