High Manifold Pressures

After doing a few runs on the dyno its been discovered that there is high pressure in the exhaust manifold. There are a million and one ideas on where this is coming from so I thought id bring it here for a more professional thought process.

I know everyone is going to want to see logs but right now the Nexus is still very weak sauce there.

EMAP sensor is about 2" from the inlet to the turbo. 13PSI springs in the wastegate. Duty cycle on boost controller is 8%. With data that can be seen there isnt any boost creep and all the fuel, ignition are on target. EGTs are low. 300 to 400 degrees. Even the AFR looks good.

At 7500 RPM and 15PSI boost pressure, EMAP is 29psi.

It should have another 1.5K rpms to go but it just isn't going there. Intake side has been streamlined and there logically isn't any obstructions that would be a restriction.

Logic tells me that the pressure restriction is DOWN stream of the EMAP sensor and its reporting the condition in the manifold.

hello have a watch of this to help understand

https://www.hpacademy.com/previous-webinars/245-tip-or-emap-explained-2/

if you think you have a restriction after the turbo try shifting your exhaust pressure sensor into the exhaust system and do a run with that

Ross

I don't believe its post turbo that's all fairly straight tubing. I am moving a Wideband sensor and that will open a port to add a sensor. Outside advice has guided me to up sizing the primaries on the manifolds. Currently they are 1.6" ID and I have ordered parts to build new 2.157" ID primaries.

I have reached out to Garrett to see if they can calculate to % of change going from the 1.01 to the 1.28 AR turbine housing would make. Its a spendy proposition at almost $1800 for the two housings and its not like they have loaner units to try.

If I'm reading this correctly Sounds to me there's a lot of back pressure in the manifold and the manifold design might be causing issues or is the turbo itself choking the flow and not flowing enough to cause all that back pressure? How's the wastegate flow in regards to the turbo?

Marty

The wastegates are on recirc, they dump into the down pipe. For sure the Drivers side setup flows good. The Passenger side is a bit wonky as its a tight fit. Its the best its going to get.

Plan to rework the manifolds pre turbo. If thats not a the fix then it will have to be an entire rework of the turbo system.

Todd,

You've not told us much info on the car?

What's the Current I.D of the manifold? What turbo/s you running? PSI/wategate pressure? Have you looked at compressor maps for said turbo/s? What size wastegates you using?

Although not likely to be an issue or cure but more of a process of elimination have you vented the wategates to atmosphere? Can you get some pics up?

EMAP of 29psi would be only 15psi gauge pressure. So that doesn't sound bad for 15psi boost. What are you expecting?

yup, I suspect there's a bit of confusion between "gauge" and "absolute" pressure - the first is relative to ambient air pressure, the second is relative to vacuum. At sea level it's approximately 14.7 PSI difference.

It would seem to be close to a 1:1 relationship, which many consider the ideal overall balance.