Now ive been having this problem from when i first got the car back on the road last year. hitting my boost cut(18psi) in 3rd@7500, i switched out the greddy 38mm wastegate for a tial 44mm(10psi spring). it was better after that but slower but its the same thing in 3rd@7500 hitting the boost cut. i also have a blitz boost controller(D-SBC with the single solenoid) that is off but i still have the lines hooked up could that be my problem or could it be the manifold?

thanks

 

run lines direct from compressor housing to the side port on the wg, that will give you the lowest boost possible, see what your max boost is then.

 

ya i'll try that

 

forgot the add i do have a very little exhaust leak right at the turbo v-band. think i need a smaller clamp. would that cause it aswell?

 

No, the only other things that would cause creep are improperly designed WG runners on your manifold, something internal in the WG (Spring, or sticking valve), or improperly sized WG - which I dont think would be the case.

 

if it is the runners would you re-do them or just go to a twin-wastegate setup?

 

I've seen this problem on a few cars were after the wastegate there was a small section of flex tubing. The internal mesh/stainless fibers/wires of the flex tubing had collapsed internally blocking flow after the wastegate. If you have one of those flex section you might want to take a peek in there.

~Mike............

 

No flex pipe after the wastegate. its a screamer

 

Why not just run 18psi, problem solved

 

I'm not sure what would be best for you. This would be worst case scenario, so check everything else you can before considering manifold design. Wanna post pics of your manifold?

Oh, and you may want to think about boost cut, if you go lean at 18psi, you may blow your engine.

 

Hey, what manifold are you using?
I'm having the same problem on my FD, even with the hks 50mm wastegate fully open(spring removed) I'm hitting 18psi.
I decided to take a look at the manifold wastegate runners( ebay stainless manifold) this is what I found.
Although the runners are 40mm the holes into the primary runners are only about 20mm.
Chinese crap!
I bought this kit from the guy in Texas who sells the Turbonetics kits on ebay.
The turbo is great but it came with a .81 turbine housing which is also too small, I've had to buy a new 1.00 A/R housing to sort it out.
Does anyone know what manifold these chinese ones are copied from?
I need for change it to a good quality one but I want to use the existing downpipe, hence I need a manifold that positions the turbo in the same place.

 

wow

 

This absolutely cracks me up (not the OP situation, but those manifolds)! When these POS manifolds first came out everyone had a hard-on over how cheap they were and like little Raccoons’ couldn't get past the shinny-ness of them. There were DIE HARD defenders of those damn things and they constantly called for "proof" and "pictures" of failed manifolds. Fast forward a couple years and all you see now on a daily basis (I view many other car forums as well) are complaints after complaints and picture after picture of cracked this and poorly assembled that...... GARBAGE!

~Mike..........

 

That's obviously a terrible mistake (someone not taking their job seriously). I would never have thought I would see something that bad...

 

ill get pics on the manifold. the boost cut isnt that hard really. alot softer then the rev limiter. the a/f under boost is like 12-13 cant remember. car is going back on the road on monday

 

Those holes in the ebay wastegate runners look to be "machined" with a quick torch blast!

 

Yes they have been blown through with the welder. lazy Bastards!

 

this pic is before i got it ceramic coated

 

Easiest fix for the manifold pictured above would be to cut the engine side of the wastegate runners/manifold and weld in a wedge of pipe so the entry to the wastegate passages has a radius to it.

There is less restriction for the exhaust to flow through the turbine housing and create boost as the manifold is now than make the 90 deg turn into the wastegate passage.

The exhaust gas is at very high velocity and you have to give it a reason to turn into the wastegate passages.

I had this same problem and a 60mm wastegate did not fix it, only easing FLOW through the wastegate solved the boost creep.

The wastegate design on these manifolds are holdovers from piston engine cars where it takes very little wastegate flow to regulate boost as the peak power and peak boost arrive at very close to the same rpm.

We are making peak boost many thousand rpm (and several hunderd hp of exhaust flow) before peak power so the wastegate has to FLOW a lot more exhaust gas.

 

forgot to mention in my first post that i wasnt hitting boost cut untill a couple weeks after i got the car back from the tuner. also i had small zap straps holding the line on the turbo and wastegate. i replaced them with hose clamps. another thing i got the car tuned when it was 20+C in the summer, now its like 10C and the air is super cool could that be another reason?

 

Got the manifold off the car the holes for the wastegate tubing are the same size as the tube. im bring it tomorrow to get them re-done... Thanks for the help