Boost Issue Troubleshooting

[Trozzle]

Here's the dyno sheet from when I got it retuned for the increased boost. Not that the boost actually climbs back up a tiny bit when the tuner took out timing in the top end...

[Harey]

Yeah it seems to be major issue. I have been reading up about it a lot recently.

(If you already know this just ignore it) My understanding is the wastegate flow is overcoming the tension of the wastegate actuator spring. The actuator spring should compress completely at the rated pressure. Although in our cases I believe the wastegate flow is pushing the wastegate open further causing the boost to drop, then the drop in boost means the spring tries to extend back in order to close the wastegate a bit, however the wastegate flow is too strong and holds the wastegate at this point, causing the boost to drop 2 or psi until redline.

I first read this thread about 'helper springs':

http://forums.nasioc.com/forums/showthread.php?t=589293

Yes they are quite ghetto and probably not what I would recommend but there is some good info here and if nothing else it at least proves what the problem is. Problems are the springs dont last too long so you need to replace them plus each spring is slightly different and can change boost differently, meaning you prob should check it on a dyno etc.

Then I found this, EVO guys using holset actuators:

http://www.dsmtuners.com/forums/turbo-system-tech/356977-holset-actuator-20g.html

Some more good info here. I have actually ordered a holset actuator from a HX35 from the US. They are supposed to have very stiff springs as they are designed to run high boost on diesel trucks etc. EVO guys have had good success. It will almost certainly require some modification to the rod though.

The goal is an actuator with max stiffness to the spring but will still open with 18-20psi of boost.

Was cheap so worth a try!

[Trozzle]

Yeah Stao was explaining it to me and it all makes sense. More exhaust flow = more pressure pushing against the wastegate flapper. This increase in pressure against the flapper on top of the boost pressure pushing against the actuator spring will make it harder to hold the gate closed as rpm climbs.

[Harey]

Here's the dyno sheet from when I got it retuned for the increased boost. Not that the boost actually climbs back up a tiny bit when the tuner took out timing in the top end...

Hmmm so the extra timing up top was causing more wastegate flow causing the wastegate flap to hold open more?? When timing is dropped so is the wastegate flow and the spring can once again pull the wastegate closed a bit to increase boost.

Its annoying cause an 18psi actuator is supposed to make a flat 18psi and then a boost controller make a flatish 6-10psi above that.

[Trozzle]

Well the spring's resistance would need to be progressive. Like I said, as revs increase so does exhaust flow. The amount of resistance required to control the wastegate grows exponentially with revs. The spring's resistance is constant. The only way to decrease the forces acting against the wastegate+actuator is to either let off the throttle, or somehow restrict the pressure acting against the actuator. This is where a boost controller comes in.

Also a current issue I've had with the wastegate setup is due to damage during transit the first time I received the turbo (security peeps opened the box for inspection and did a shit job of positioning the turbo when they closed it again, wastegate took a beating). My wastegate wasn't closing completely. Even though it was as closed as you were going to get it, 99% of the time the flapper wasn't creating a seal. This was allowing a small amount of exhaust to pass through the wastegate even when not on boost. The moment exhaust begins to pass the wastegate, it becomes monumentally more difficult for the actuator to hold it closed.

This is why people always say to use an actuator with a spring resistance CLOSEST to the boost level you wish to be running, then use a boost controller to bump it up and control it. Otherwise we'd all be running 5psi actuators and controlling the boost up to 20psi.

[Harey]

Well the spring's resistance would need to be progressive. Like I said, as revs increase so does exhaust flow. The amount of resistance required to control the wastegate grows exponentially with revs. The spring's resistance is constant. The only way to decrease the forces acting against the wastegate+actuator is to either let off the throttle, or somehow restrict the pressure acting against the actuator. This is where a boost controller comes in.

In my current situation with only the actuator (no boost controller) it makes 17.5psi and then drops to 15.5psi. When I hook up a boost controller it will make say 20psi and then drop to the same 15.5psi. I believe that in my situation it does not matter what pressure the actuator is getting it would still only make 15.5psi up top. To test this I could take the hose off the actuator so it never sees pressure but it would prob make 25-30psi for a quick moment and then drop to 15.5psi. In my case the wastegate flow is completely overcoming the actuator spring.

What we need is a super stiff spring that still moves at the same rate with the same pressure. This is what I am hoping the holset actuator will provide as they frequently run 20-30psi with internal wastegates. If you read that EVO link a lot of people were having the same problem as us and solved it with the holset actuator up to about 23psi, above that they were still getting some boost drop off.

[Harey]

The helper spring also makes a lot of sense because it is not affected by the pressure received at the actuator.

[hypergear]

I think there is a way of fixing it by running 2x actuators without the gate controller. means 2x actuators gets connected to 1x extension rod. I'm pretty sure that would work, just need to engineer the bracket that fits the turbo and into the engine bay. Or run external gate plumbed back, I will design a housing for that to suit ATR43 series when I get back. In this case you can possible run a 50mm external gate with a .63 rear housing with G3 CHRA that should make 300rwkws+ with out much knock while gain lot better response.

[Rolls]

Here's the dyno sheet from when I got it retuned for the increased boost. Not that the boost actually climbs back up a tiny bit when the tuner took out timing in the top end...

Less timing means more energy out the exhaust so you'd expect it to climb, unless the boost controller has multiple rpm points where you can tune the parameters there isn't any easy way around this. Any reason they didn't just richen the mixture up instead?

[Harey]

Less timing means more energy out the exhaust so you'd expect it to climb, unless the boost controller has multiple rpm points where you can tune the parameters there isn't any easy way around this. Any reason they didn't just richen the mixture up instead?

If less timing means more energy out the exhaust, the extra exhaust flow would push the wastegate open (lowering boost) as the spring is already beyond its limit.

If less timing means there is less pressure spinning the turbo then it all makes sense as we said.

[Rolls]

depends if the wastegate is choking or not, if it isn't then it won't push it open and it will just go out the turbine causing a boost increase, can get either happening really.

[Trozzle]

Less timing means more energy out the exhaust so you'd expect it to climb, unless the boost controller has multiple rpm points where you can tune the parameters there isn't any easy way around this. Any reason they didn't just richen the mixture up instead?

I've heard that before too. the only thing that I can't make sense of with it is that we add timing to gain power, so why would less also make more? Also, why do we add timing in midrange? For improved torque? I thought torque was constant for a given power@rpm, so doesn't that also conclude that power at that particular rpm increased when timing was added?

But yeah main point is that the same tuner also mentioned that ripping out a heap of timing somehow increased peak power, and this was used as a shortcut for dyno queens or something...

Also, I'd go find the AFR sheet as well from the hypergear thread, but cbf. Mid to high rpm the mixture was roughly 11.5AFR, then at the end of the run it was down to about 11.1AFR

[Rolls]

Boost increased, not power, power dropped as timing went down.

[Harey]

depends if the wastegate is choking or not, if it isn't then it won't push it open and it will just go out the turbine causing a boost increase, can get either happening really.

The fact that the boost level is dropping as the rpm increase means that the wastegate flow is overcoming the actuator spring and pushing the wastegate flap open. Is this what you mean by wastegate choking?

It will only cause a boost increase if the actuator cant control the boost.

[Rolls]

Yeah that is what I mean, I don't see any other explanation for the rising boost level at the very top end though.

[Trozzle]

Boost increased, not power, power dropped as timing went down.

sorry my bad. lol then consider what I blurted a backup and detail of what you said

[DVS JEZ]

I've heard that before too. the only thing that I can't make sense of with it is that we add timing to gain power, so why would less also make more? Also, why do we add timing in midrange? For improved torque? I thought torque was constant for a given power@rpm, so doesn't that also conclude that power at that particular rpm increased when timing was added?

But yeah main point is that the same tuner also mentioned that ripping out a heap of timing somehow increased peak power, and this was used as a shortcut for dyno queens or something...

Also, I'd go find the AFR sheet as well from the hypergear thread, but cbf. Mid to high rpm the mixture was roughly 11.5AFR, then at the end of the run it was down to about 11.1AFR

its not just torque but power also, midrange is a very important but deadly part of the tuning process, midrange is normally where max torque is which is also max Volumetric Efficiency(cylinder filling) as this is the sweet spot for the cams.

therefor max cylinder filling means max heat, and max cylinder pressure which if there is any detonation or pinging from over advanced timing etc the cylinder pressures sky rocket and break pistons, rods and bearings.

[hypergear]

More timing + Most boost = more power. Generally you would want to set more timing as possible with out "knock" also within the range which the engine is capable of handling. With ATR43G3 model you might want to ask your tuner to advance more timing around the 4000RPMs mark which would give you stronger mid rang, the .70 58 Trim version made 30kws difference.

Also it looks like your tuner has deliberately tuned your car just under 300rwkws. So depending on how comfortable he is with your engine you can run those waste gate studs to creep more boost up top.

[Rolls]

What happened in this case was less time = more boost but still less power. I was just commenting on a possible reason for the boost increasing with less timing.

[DVS JEZ]

im having a mental blank to explain it in detail, but retarding the ignition timing increases the exhaust temperature and hotter egt's cause the turbo's to spool faster