Overboosting.

[ODessA]

you are driving along in your turbo car, there is no vacuum leaks on your car, your turbo has an actuator of 0.7 bar, when you accelerate through the rev range your boost sits steady at 0.7 bar until you get to about 5800rpm, and then your boost starts rising out of nowhere and you end up with 1.3 bar of boost by the time you get to 7500, you have no boost controller at all just a hose from compressor housing to actuator.

What is the problem?

[GTScotT]

Need Moar info.

What car, what mods?

I get the impression the car is not stock.

[R3N3]

do you have a divided front pipe?

[chocco]

Need more information.

[ODessA]

its a gt starlet, it has a blitz turbo on it with a stock actuator, there is an intercooler bigger injectors but thats about it nothing that should effect the boost, the dump pipe is not split.

the stock boost solenoid has been completely bypassed (it was doing the same thing with it anyway) and boost control should be soley off the actuator at 0.7 bar, which it does until it gets to about 5800 and then its like the wastegate is either closing or not opening far enough to keep that pressure and the boost climbs drastically till well over 1 bar if u let it.

i dont know what other info to give you guys

[Trozzle]

When did it last work?

Pretty much something is restricting how much the actuator can open the gate - so in my opinion it's either boost controller (which you don't have), actuator itself, actuator rod preload, or gate fouling on something. Well also, could be that the internal gate simply isn't big enough, but I doubt that.

If you can get to the turbo/actuator while it's on the car, I'd recommend disconnecting the actuator rod from the wastegate. Once it's off, ensure that the wastegate can open and close freely. Also ensure that when you are putting the actuator rod back onto the wastegate, you need to pull the rod out against the spring roughly 3mm. If any more, then overboost is possible.

[MrStabby]

you are driving along in your turbo car, there is no vacuum leaks on your car, your turbo has an actuator of 0.7 bar, when you accelerate through the rev range your boost sits steady at 0.7 bar until you get to about 5800rpm, and then your boost starts rising out of nowhere and you end up with 1.3 bar of boost by the time you get to 7500, you have no boost controller at all just a hose from compressor housing to actuator.

Since you say boost is steady at 0.7 (so, lets say its at 0.7 from say 3000-5800) this indicates the boost control is working, but then runs out of ability to bypass enough through the wastegate at 5800. So i'd check that the wastegate flap can open the whole way (if you have a hand pump just connect it to the actuator and watch it move as you add pressure). It may be fouling/getting stuck part way open. Other than that it may simply not be big enough, but usually jap turbos have well sized gates....

[ODessA]

What did it last work?

Pretty much something is restricting how much the actuator can open the gate - so in my opinion it's either boost controller (which you don't have), actuator itself, actuator rod preload, or gate fouling on something. Well also, could be that the internal gate simply isn't big enough, but I doubt that.

If you can get to the turbo/actuator while it's on the car, I'd recommend disconnecting the actuator rod from the wastegate. Once it's off, ensure that the wastegate can open and close freely. Also ensure that when you are putting the actuator rod back onto the wastegate, you need to pull the rod out against the spring roughly 3mm. If any more, then overboost is possible.

this turbo has just gone on with this actuator already on it when i bought it, the turbo has just been rebuilt but clearly the actuator is questionable, i will follow your advice and see if theres anything fishy going on with the actuator or something blocking the gate opening, the turbo is pretty easily accessible where it is atm.

thank you very much!!!!!!!!!!!!

[Trozzle]

No worries happy to pass on knowledge that I needed not all that long ago

[turboedsloth]

what diameter is the dump pipe? is there a bend right at where it comes out of the exhaust housing? If so how sharp is the bend?

[ODessA]

ok guys some progress has been made but im not out of the woods yet.

if you look at the picture below it appears the gasket between turbo and dump was fowling up the wastegate opening, note that the actuator arm seems to be bent towards it a bit which would not have helped.

now after this photo i have resolved this problem and as far as i can tell it definately clears it now and can open the whole way, but still i am having the same problem so now i guess the question is,

has this been fouled with all that boost on it effected the integrity of the actuator ?

i dont have a pump to test it, and using my hand to move the actuator is very difficult in the position its in and i dont think its good for it anyway.

i have another stock actuator to replace this one, but would you believe the one on the stock turbo is a little bit different as the bottom of the actuator arm is just a hole, on this turbo the wastegate arm has the hole..

Edited December 1, 2010 by ODessA

[DVS JEZ]

take the arm off the wastegate flapper and ensure it opens all the way freely and closes easily, then refit the arm

[maddowse]

wastegate flap seems bent in also ??

[ODessA]

i did take the arm off, it seems to move perfectly freely and goes atleast 180deg

[Pal]

has the car been tuned with this turbo?? sometimes either too rich or too lean can cause overboosting (cant remember which one).

[ODessA]

this turbo and ecu comes as a kit from blitz for a starlet, its tuned for it, and while japanese fuel is better than here, i dont see it causing this, i can put the stock one in to test.

this turbo isnt a whole lot bigger than stock, ive seen people run them on a stock ecu fine before, its only good for a little over 200hp, but thats plenty cause starlet weighs nothing

[DVS JEZ]

take the dump pipe off and see if there is any room for improvement at the wastegate hole, like can it be ground out 1mm or so to help?

we had a s13 that would boost creep to 21psi from 18psi, we found the cheap ebay manifold that was to suit a 38mm gate had a 29mm hole, we ground it out to 31mm and it completely fixed the issue,

if you do grind it out make sure you take the housing off the turbo 1st

[Sparky206]

I've had this problem for ages in my rb25. I have tried everything, different actuators, a high flowed turbo, a split and bellmouth dump pipe, but nothing stopped the creep. The only thing that i could find that made and difference was by placing a 2.5" restriction plate at the end of my 3" exhaust. That allowed the car to hold a steady boost level all the way to redline. I can't explain why, found the idea from a few supras who had the same problem. I have a feeling its to do with the tune, as im running stock ecu with mods, but when i get it re flashed i'll just up the boost anyway and let it do what it wants

[Trozzle]

I'd sooner bore out the internal wastegate hole than restrict the exhaust to control boost....lol

[DVS JEZ]

yeps