TurboTommy

What technical reason would there be for you guys to say that the wastegate isn't too small.
If I floor it at about 3,500 RPM I'll hit the 10 - 11 psi boost (so this is just the spring pressure; boost signal directly from the turbo discharge). It will hold this until about 4,500 RPM. Then, boost will rise rapidly from there.
I don't see what else it could be.
If you's think that a 38mm wastegate should be fine for me; then I ask why would anybody run a 46mm?

Paulyy

I get your point. Did this happen straight away with the 3L or just recently ?

David Floyd

Agreed size is not the issue, maybe a faulty wastegate but not size, as I mentioned my tiny 35 works perfect and my car is not stock.

Duke

First of all, I thought your 3l engine have been around for some time, or is this a new build? Or did something happen all of a sudden?

What wastegate do you have, Lindsey? If so, it should be 40 mm?
It's not like you have a 25 mm wastegate there, even if your wastegate was slightly too small the boost wouldn't sky rocket like that.

When I think about it, I have tuned 1 3.0l engine with a Lindsey dual port gate without issues and 1 3.0l engine with Tial 38 mm wastegate and it can be run with as low as 0.7 bar of boost without creep so yes I would say I have enough to stand on when I claim it's not the wastegate size that's the issue here.

Marketing..?

Fishey

check to make sure you didn't pinch the diaphram between the top part and the base (were the screws hold it togeather) I have seen this happen many times. This will not allow it to open properly.

-Your Pal
Fishey

TurboTommy

Yes, I've had my 3.0l for over 3 years.
But, I have made some changes recently. I've changed turbos, changed to this LR dual port wastegate (it's 38mm) with its own dump pipe and mini-muffler.
My entire turbo system is very efficient with as little pressure drop as possible, starting from my huge air filter all the way back to the tailpipe. I'm very close to 1:1 boost/back pressure. I'm guessing it takes less exhaust energy to make boost; therefore more exhaust needs to go through the wastegate.

But, your experience with 3.0l and wastegate size is what I was looking for. I definitely see what you and others are saying. After thinking about it some more, it does seem strange. It's almost as if the valve isn't opening all the way, but when I tested it on the bench it seemed fine. I wonder if something is different when installed on the car.

thingo

I'm interested to know what turbo/ exhaust system you using to achieve 1:1 boost/back pressure? What is you back pressure at peak power?

Duke

That's a good thought, it would also mean less pressure on the wastegate valve.
But something else is probably up. Sometimes it's easy to miss the little things, like checking that the turbo pressure line from the intercooler pipe to the wastegate is not pinched or broken.
What turbo do you have?

Chris White

You are describing the symptoms of a backwards wastegate.
Once the flow and pressure get high enough they push the valve closed.

If you were ‘out flowing’ the 38mm design I would expect to see a slow increase in boost not a quick spike.

brrgrr

I had the exact same symptoms that the original post is describing and I just installed a new black **** MBC and that solved the problem - boost shoots up to the set value and stays rock solid from there up to red line. I was shocked at just how dirty the inside of my original MBC was - it was filled with all kinds of debris and soot.

TurboTommy

Turbo is a gt35 with a #10 hot-housing on a p-trim wheel.

I checked the boost line going to the wastegate; everything is proper and no leaks

Another thing: how big is the pipe going from the cross-over to the wastegate? It looks kinda small, and the exhaust flow sort of runs backwards ( really sharp corner from the cross-over)

Thom

Tommy, did you solve the problem?

Paulyy

nice digging up!

I experienced boost creep when my bolt came out holding the gasket after the wastegate which moved the gasket down blocking the flow path out from the wastegate causing boost creep.

TurboTommy

Yeah, it took alot of doing, but I did eventually get it sorted out.
The bottom line is that as one gets nearer and nearer to the coveted 1:1 ratio, the flow to the wastegate needs to be symetrical and have good priority.
Think about it; if the turbine inlet pressure is relatively low why would the exhaust flow want to go anywhere else but through the turbine; and because once the turbine is spinning, relatively small changes in faster turbo speed brings about larger changes in boost pressure, hence the runaway boost (especially if the compressor side has more than capable flow capacity).


I first went with a bigger wastegate; only helped the problem slightly.

Then I had these header$ fabbed up with the wastegate tie-in directly off the secondaries:

Thom

That is great feedback, thank you.

I gather from the twin inlet of the cross pipe that you are still running stock headers?