Overboost Problem - Need Help

[LittlesumoS15]

Hi,

I'm using a HKS GTRS with HKS 1 bar adjustable actuator which I've noticed a few SAU members use so I'm hoping you guys will be able to help me with an overboost problem I’m having with my S15.

Had the car tuned previously and it sat on 15.5psi flat without any problems. Had it retuned recently and it started overboosting to 18psi at high revs over 6500rpm in 3rd and 4th .

Things I’ve done to find the problem:

1) Unplugged the electronic boost controller and ran the actuator off the intercooler piping as the pressure source. It should only boost to what the spring in the actuator can hold but it still ran up to 18psi. So overboosting wasn’t solenoid/EBC related.

2) Took the adjustable actuator arm off the wastegate and tested the flap wasn’t hitting on the dump pipe or jamming. It opened all the way easily. The rod was also movable and not jamming.

3) Adjusted the HKS 1 bar actuator by lengthening the rod to see if that would reduce the boost. I was expecting atleast a 1psi reduction after 3 full rotations but nothing, still overboosting.

So I’m leaning towards the problem being the actuator even though I bought it brand new. Must be only 6-8mths or so old. Do these actuators often fail?

Anyone had a similar problem?

What should I try next? Replace the actuator?

Any help would be much appreciated.

Cheers,

[paulr33]

its unlikely that it has failed, its a pretty simple device

its likely its been fitted wrong, loose, mangled, fiddled with or has some play in it etc

if the actuator cant hold it correctly, the boost controller has no hope

is it a genuine std GTRS or has it been modified etc?

what sort of dump/front pipe?

[LittlesumoS15]

its unlikely that it has failed, its a pretty simple device

its likely its been fitted wrong, loose, mangled, fiddled with or has some play in it etc

if the actuator cant hold it correctly, the boost controller has no hope

is it a genuine std GTRS or has it been modified etc?

what sort of dump/front pipe?

Thanks for your reply Paul33 - big fan of your PowerFC FAQ btw .

Yeah I've heard it's pretty uncommon for the actuator to fail. Only thing I can think of is the diaphragm may have a problem.

I bought the HKS GTRS brand new, genuine, standard trim, with the actuator already attached. I fitted the turbo myself and no one else has touched it. But I didn't check the actuator bolts tho. I assumed they were already tight.

I've got a cheapo one piece dump pipe + front pipe. It has a bell mouth opening and I can move the wategate flap manually without any interference. The flap can open right up so I don't think it is hitting the dump pipe or catching on it.

I will check it for play or movement on the actuator bracket tho. Thanks for that.

Anymore ideas?

[paulr33]

when boost exceeds what is set by the actuator and its static until a point, like yours

it sounds like the exhaust backpressure increases and thus it yields more compressor flow - ie it cant scavange quick enough

[PM-R33]

Personally I find with mine that the tune plays a big role in how much boost it runs. When my tune was crap running rich it would overboost hardcore (Could barely keep it under 20psi).

I've been slowly tuning my own car with the Vipec and tuned it nicely on about 1bar with the boost controller disconnected (just running actuator) without boost issues. Next im doing the high boost tune for it.

There is a lot of threads about GT-RS's overboosting a lot, personally I think the internal gate in them is shit when trying to run low boost.

Edited September 25, 2010 by PM-R33

[LittlesumoS15]

when boost exceeds what is set by the actuator and its static until a point, like yours

it sounds like the exhaust backpressure increases and thus it yields more compressor flow - ie it cant scavange quick enough

Hmm I think I understand what you are saying but I'm a bit of a technical noob I'm afraid. Could you explain it for an idiot?

I'm using a stock manifold which probably doesn't scavange very well.

I'm also using Greddy Easy Cams - IN 256 EX 264 10.5mm lift. Would that be a factor?

If this is the case, what would the solution be?

In regard to movement of the actuator bracket etc, I've had a quick look and I doubt that would be the problem...

[Supa Steve]

The newer tune has made the engine more efficient, the cross sectional area of the wastegate is not sufficient to bypass the turbine.

Currently having the same issues with my new set-up.

Im finding with the softer tune it holds well as soon as the numbers become more aggressive it struggles to hold steady.

The guy who built my engine had the same issues in his car and they had to back off the tune to limit it to a constant level.

[PM-R33]

Hence it's easier to just run 18-20psi all day everyday like mine lol.

[kwickr33]

If wastegate and actuators operates, all it means is the wastegate whole on those turbos are too small for your setup.

Edited September 25, 2010 by kwickr33

[LittlesumoS15]

The newer tune has made the engine more efficient, the cross sectional area of the wastegate is not sufficient to bypass the turbine.

Currently having the same issues with my new set-up.

Im finding with the softer tune it holds well as soon as the numbers become more aggressive it struggles to hold steady.

The guy who built my engine had the same issues in his car and they had to back off the tune to limit it to a constant level.

Oh I see, that makes sense. So the best/easiest solution is a more conservative tune?

Thanks for your reply.

[LittlesumoS15]

Hence it's easier to just run 18-20psi all day everyday like mine lol.

lol I think you might be right...

[snozzle]

tiny hole in diaphram? crack in vac line? time for external gate?

[PM-R33]

Nah like I said, just don't try and run low boost and you will be fine, stop being soft. 20psi is the new black.

Think of which situation is more likely going to get you laid:

SITUATION 1

16yo girl: "So how much boost you running hun?"

You: "Ohh, umm, i'm just running like 12psi, sometimes I run 13psi if it's a bit cold..."

16yo girl: "......." *Get's out of car and jumps into a VL turbo that has a dose pipe*

SITUATION 2

16yo girl: "So how much boost you running hun?"

You: "20psi BITCH!"

16yo girl: *Starts undoing your belt*

I rest my case.

Edited September 25, 2010 by PM-R33

[discopotato03]

It may be an idea to find out exactly what the changes were to the tune .

It's interesting that people think these turbos are prone to over boost , not one I'm familiar with though I haven't inquired much about them either .

To the OP , being on an SR20 you would be using a T25 flanged turbine housing and from HKS it would be a 0.64 A/R one . Garrett do an optional larger 0.86 A/R one as well as a similar 0.64 one .

The larger housing is reasonably large for that GT28 turbine but not what you'd call huge in the scheme of things .

What it would do is slow the turbine slightly and ultimately you would make more power with it .

The secret to picking up the bottom end is to get it tuned with generally more advance timing in the off boost and transition stages , I found with the 0.86 housing I was able to to increase the timing 4-6 degrees when I changed from a ceramic RB20 BB turbo to a GT2860RS one . There is a big difference in the turbine housings (RB20 to 0.86 GT28) and the timing wasn't so much advanced up as being less retarded for the exhaust restriction if you know what I mean .

Cheers A .

[LittlesumoS15]

Nah like I said, just don't try and run low boost and you will be fine, stop being soft. 20psi is the new black.

Think of which situation is more likely going to get you laid:

SITUATION 1

16yo girl: "So how much boost you running hun?"

You: "Ohh, umm, i'm just running like 12psi, sometimes I run 13psi if it's a bit cold..."

16yo girl: "......." *Get's out of car and jumps into a VL turbo that has a dose pipe*

SITUATION 2

16yo girl: "So how much boost you running hun?"

You: "20psi BITCH!"

16yo girl: *Starts undoing your belt*

I rest my case.

Buhahahahahahaha

[LittlesumoS15]

Does anyone have an opinion on whether a divorce dump pipe which splits the flow of turbine and wastegate gases like the CES ones would help reduce boost creep?

[PM-R33]

If you are having overboost problems on a bellmouth style dump pipe, going to split dump won't fix it (could in fact make it worse). I used to have one on mine, wastegate flap fouled on it so I fixed that up but the split pipe was just way to small to flow enough gas out so I went to the bellmouth.

[R31 POWER]

Does it have a cat? A mate of mine was having boost issues with the same turbo. Fitted a cat and he could control boost I also had a similar prob with a hks gt2535, removed cat and the lowest boost i could run was 14/15psi with a stock rb20 actuator!

[LittlesumoS15]

Does it have a cat? A mate of mine was having boost issues with the same turbo. Fitted a cat and he could control boost I also had a similar prob with a hks gt2535, removed cat and the lowest boost i could run was 14/15psi with a stock rb20 actuator!

Yeh but I have a high flow metal cat which looks like it flows really well, perhaps too well. I'm going to try stick the restrictor in the muffler and see if that controls the boost.