968 Turbo boost problems whilst mapping

[Thom]

@Rickuk1, any progress? I'm sure I'm not the only one intrigued by how well your twin scroll set up will perform.

[Thom]

I remember now the thread on the "other" board on this build, dating from 2018.
Rod had recommended "no bigger than 41mm id on the crossover pipes, that should work out to 1.75" tube". Is this what you ended up using?

Does anyone with a stock crossover pipe lying around could measure the outer diameter? I can't find data on the inner diameter. The double wall construction does not make measurement easier short of cutting open a crossover pipe...

[Rickuk1]

Hi my mechanic is having problems logging on to carpokes for some reason I want him to join the conversation as he can answer more of the technical questions than myself. Yes Thom that is my thread from back in 2018, nice quick build. We think the problem might be with the setup in the ecu rather than a physical mechanical problem. Ie the parameters of how to set up the boost. At the moment the car achieves spring rate pressure very early in the rev range but does not progressively build boost and then at approximately 4000 rpm it starts to build more boost. It’s like something is not allowing the boost to increase until after 4K, but what this is we do not know we are hoping it’s a changeable setting within the ecu. The other problem we were having was the vario cam was not working but this has been fixed now we also think the vacuum lines on the waste gates were piped incorrectly but this to has been rectified we believe. Any ideas on the ecu settings we are not finding it easy to get support on the vems ecu.

[Rickuk1]

I remember now the thread on the "other" board on this build, dating from 2018.
Rod had recommended "no bigger than 41mm id on the crossover pipes, that should work out to 1.75" tube". Is this what you ended up using?

Does anyone with a stock crossover pipe lying around could measure the outer diameter? I can't find data on the inner diameter. The double wall construction does not make measurement easier short of cutting open a crossover pipe...

I remember now the thread on the "other" board on this build, dating from 2018.
Rod had recommended "no bigger than 41mm id on the crossover pipes, that should work out to 1.75" tube". Is this what you ended up using?

Does anyone with a stock crossover pipe lying around could measure the outer diameter? I can't find data on the inner diameter. The double wall construction does not make measurement easier short of cutting open a crossover pipe...

Yes we used 1 3/4” tube

[Thom]

Re controlling the wastegates, I suppose you have seen this diagram already?

dual wastegate compressed vacuum.jpg (24.83 KiB) Viewed 2591 times

How early in the rev range do you reach the wastegate spring pressure?

[Willy Wabtec]

Hi Chaps - apologies for the delay, I had some log in issues -

I’ve built this car for Rick, I’ll read through the replies later and try and fill in the gaps.

I did a run with it a couple of weeks ago with a mechanical gauge plumbed in to monitor the boost pressure (I’m working alone most of the time and I’m not that familiar with VEMs to log the boost readings yet)

So makes 0.7bar (wastegate pressure) fairly early on, then stays at that untill about 4,000rpm then shoots upto 1bar boost and holds that untill max rpm.

Boost graph request (which I’ll take a picture off) is pretty flat - calls for 1bar boost from early on.

My suspicion is that the N75 valve is not “active” below 4,000rpm because the previous car the Ecu was on had a bigger turbo and standard internals so would be more “sympathetic” torque wise.

If any of your are a whizz with VEMs and have team viewer and are happy to spend half an hour having a look at the boost control PID’s I’m fairly confident the issue can be solved

[Thom]

@Rickuk1 & @Willy Wabtec : PM sent.

Where do you have the "Boost Valve OFF Below This Pressure" set at?

[ealoken]

I have 1.2 bar boost with my GTX3576 Gen2 around 4000 rpm.
the 4 cyl will never make a huge amount of power below 4000.

[Thom]

I have 1.2 bar boost with my GTX3576 Gen2 around 4000 rpm.
the 4 cyl will never make a huge amount of power below 4000.

An oversized turbo such as a GTX3576R Gen 2 on a 2.5 8V engine will hardly ever shine for sure.

[Willy Wabtec]

@Rickuk1 & @Willy Wabtec : PM sent.

Where do you have the "Boost Valve OFF Below This Pressure" set at?

Hi Thom, I emailed David the config file, I found this in the boost PID’s which may or may not be relevant-

So the boost control valve is “off” untill boost pressure reaches 1 bar ?