external wastegate overboosting(creeping)

[hayai]

car went on the dyno yesterday and had some serious overboosting issues which is due to the position of the wastegate on the manifold (i kinda saw this coming) however since i have to change the position i have also been recommended to change my wastegate to a bigger one (currently 38mm) , i'm looking at running close to 30psi with a GT30R. Can anyone give feed back on PROVEN combinations ?

so i guess what i want to know is if a 38mm will handle holding 30psi out of a GT30R?

ok we looked closer at the manifold and seriously doubt it's the position of the wastegate that is causing the overboost.

Anyway here's what is happening exactly

accelerate , get boost by 3000rpm , get full boost by 5000rpm wastegate is open , holds boost steady at .7bar until it hits about 6500rpm and then it just overboosts.

any ideas ?

[zeroyon]

although I have a GT35R i have the exact same issue.

Starts at 10 psi, gate open hits about 5500 and starts climbing to sky.

Even with a 50mm greddy gate still no joy.

There a lot of things to consider and I tried a lot.

I would not expect a 38mm gate to be big enough.

post up some pics of how the gate comes of the manifold as well.

[hayai]

it's basically horizontal to the flow of the gases , not in opposite direction though.

i just had an apifony (however u spell it)

the car had been tuned once before and it didn't have any boost creep issues. the only difference in engine between the two tunes is the wastegate gasket. which blew (as u know butters since i was asking for one) i managed to get one from grant but it was a completely paper one , the old one was partial paper partial metal.

as i said the first tune i had no problem with overboosting but this second one i did , and the only difference is bottom end and that gasket.

would i be right to assume that the new gasket is leaking under high rpm (pressure) ?

[hayai]

gah wait a minute

just thought about what i just said ... if the gasket was leaking then it would be loosing boost not gaining it :S

[zeroyon]

I doubt that. By rights if it is leaking you will get less boost, not more.

So you say you had this combo working to full revs and now it doesnt ?

only change the gasket ?

[hayai]

gasket and rebuilt bottom end (since i blew up the first bottom end)

and yeah as i said i just realised what i said didn't make sense hehehe

[zeroyon]

have you got a power comparision at say 4500 from old bottom end to new bottom end ?

if the new engine is fresher and making more hp its going to create more exhaust gas to get rid of.

[hayai]

butters got a msn buddy , this is tedious

[zeroyon]

lol, no ****

[hayai]

yeah i agree it may be making more exhaust gases , but since there wasn't a sign of overboosting on the first bottom end ... i find it hard to believe that the new bottom end would through it out by this much though my knowledge is pretty limited

[zeroyon]

Pm sent