Two Level Boost

[Nicely]

So what else could cause the turbo to suddenly spike 0.3+ bar like I'd just pressed a 'TURBO' button on the dash? Literally. It happens so quick that the controller and actuator haven't got time to compensate...

 

[Meddy]

So what else could cause the turbo to suddenly spike 0.3+ bar like I'd just pressed a 'TURBO' button on the dash? Literally. It happens so quick that the controller and actuator haven't got time to compensate...

Im not saying it couldnt be boost creep only that when the wastegate is disconnected you will still see boost.

I do find it a bit hard to believe that the addition of a tubular manifold would give you such an issue as compared to my setup without. I would imagine if it was the manifold at fault you would expect to see dozens of 14 owners with the same issue.

Is it possible for you to get hold of a different EBC and give that a go?

Thinking as Im writing this but is the T28BB a twin scroll housing and the non BB unit isnt? Next question does the wastegate vent from only one scroll or from both?

 

[Nicely]

The T28BB looks virtually identical to the T28. The only differences that I can tell, apart from the obvious, are the oil feed located slightly differently and the wastegate being separated from the turbine by a curved metal wall. There is no wall on the T28.

Most of the SXOC people running a tubular mani are running a T28.

 

[Meddy]

The T28BB looks virtually identical to the T28. The only differences that I can tell, apart from the obvious, are the oil feed located slightly differently and the wastegate being separated from the turbine by a curved metal wall. There is no wall on the T28.

Most of the SXOC people running a tubular mani are running a T28.

You mean there is a dividing wall down the middle of the turbine housing? i.e. twin scroll

 

[Nicely]

If that's 'twin scroll', yes As to whether it vents from both -

 

[Meddy]

If that's 'twin scroll', yes As to whether it vents from both -

Usually not, which is what I was thinking. Now please stop me here if any point you think Im talking b@:locks.

Ok on the standard mani from memory all 4 exhaust branches feed into the turbo mount so the gasses will mix before entering the turbo. On the tubular manifold the branches are split and feed in in pairs. So on the tubular manifold the wastegate is only venting 30-40% of two cylinders flow and not 30-40% of the overall flow. I am no aero expert so will check my thinking with them, but it could be an explanation as to why I never had issues and you do.

 

[Nicely]

i.e. you where running a standard mani whilst I have tubular...

 

[Nicely]

Hmm. This is the turbo mount of the tubular mani. Looks as though it does mix before entering the turbo...

 

[Meddy]

Hmm. This is the turbo mount of the tubular mani. Looks as though it does mix before entering the turbo...

Still looks like there may be two distinct seperated flows there. It would be interesting to see the same view of the stock manifold if you have it kicking around.

Other than this I cant really see any reason it would behave any differently than with an OEM manifold.

 

[Yakozan]

From memory i think the stock manifold has a dividing wall in the outlet. so there is 2 outlets so to speak.
Not 100% on this, but about 90%.

 

[Nicely]

More restricted? From all accounts, the low-down torque is better on the standard mani... Not sure if that has a bearing...

 

[Nicely]

Here's the wastegate side...

And a look inside the exhaust inlet...

Its one passage, with the wastegate opening into the first part of it (where my finger is).

 

[S15R]

Boost creep, I'm told. Make the wastegate bigger or get an AVCR to control to boost at specific rpms...

Tested it at lunchtime with the actuator disconnected and the wastegate tied open. Pulled 0.5 bar at peak. Should be 0...

any turbo with internal wastegate will run some boost it cant be 0 bar whereas with external waste 0 bar is possible

btw what dump pipe are you using? split ones? maybe the wastegate is hitting something therefore wastegate isnt fully open? i m just guessing

 

[Nicely]

Unfortunately, due to the manner in which it does this under full boost, i.e. in under a second, its a bit of a problem. If it introduced this a little slower, it could be contained.

It was suggested that I use an AVCR to control the boost at a specific rev point. But this is a bit defeating. I'd have boost of, say, 1.2 bar up to about 4500 rpm, then it would have to be backed-off to 1 bar. That's a noticable loss of power at the point where most power is usually produced...

 

[S15R]

time to upgrade the turbo

 

[Nicely]

time to upgrade the turbo

Yep. I know a few people who have done that and had exactly the same problem. They landed up having to fit external wastegates. As the turbo I just fitted has only done 5.5k km, I'd rather just fit the standard mani if that will sort it...

 

[Nicely]

Left it a fraction longer before lifting off this morning and it spiked to 1.5 bar...

 

[Topper]

I've always like the sound of a T51R BB Kai

 

[Meddy]

Ok Ive had a chat to a few people and engaded my brain and consensus is the manifold will have bugger all effect and is very unlikely to be causing this issue.

It cant be the extra flow causing problems as if this was the case it would be a gradual steady build not a instant spike. With it being such a big rapid spike it kind of points towards the EBC. However it must be a faulty unit as it cant be a short or earth fault otherwise Id guess it would fail safe and go fully closed hence reducing your boost.

Thinking is the controller works by interupting the wastegate boost feed, feeding it through a small orrifice and then bleeding off air by opening a valve to fool the actuator into remaining closed. So to increase boost pressure the valve needs to open and to decrease pressure close to increase the feed to the actuator can. So if the EBC is for whatever reason getting very confused and suddenly going wide open this could give you spiking. Other possible suggestion is some kind of contamination in the solenoid.

Well thats my best guess and the easiest way to prove it is to bung on another EBC. You may have already said but if you run with the EBC off does the boost build smoothly to wastegate set pressure with no spiking? IF this is the case it kind of reinforces the idea its a control problem and not mechanical.

Again this could be nonsense and Im happy to be proved wrong, but I think before you lose the manifold its worth trying a different controller.

 

[Nicely]

OK. To throw a spanner into the works...

It does the spike when running with the EBC off and just the actuator adjusted up. It also does it with the EBC bypassed through my own finely adjustable version of the Apex Performance boost valve...

A thought has occured to me about something which may *possibly* have an effect. I'll try it at lunchtime. Its off on a complete tangent, but is linked to the car's boosting...