TurboTommy

This question goes out to those have experience needing to go to a 46mm wastegate and the reasons why; probably to the fellow 3.0l folks.

Thom

As far as I have heard, the 46mm makes a point on cars than have to sustain prolonged periods of boost in extreme conditions - track cars.
My 38mm has been doing fine both on my 2.5 and 3.0. Haven't had any issue so far in about 30k road miles.

Paulyy

What i've read (correct me if im wrong) but the 46mm will open later then the 38mm so it will spool faster and hold boost a little better. the 38's valve needs to travel more to let more exhaust out then the 48.
e.g. the MBC is set to make 15psi. 38mm will open at 11psi and the 48 will open at 13 @ WOT
remember these are just examples and not actual figers.

TurboTommy

Well, for example, one situation where one needs a bigger wastegate is on a larger engine running low boost (lots of exhaust flow from engine, but alot of it needs to be bypassed around turbine).
I've got a 38mm but have what seems to be boost creep.
It "creeps" quickly, though. At 4,500 to 5,000 RPM (around there) the boost goes from about 16-17 psi to over 20 psi within 3-400 RPM.
I just want to make sure that in fact my wastegate is too small before I spring for a bigger one.

TurboTommy

Also, I pressure tested my lines having to do with boost control and no leaks; so that's not the problem.
Isn't there a few guys here that run a 38mm on a 3.0 liter motor, and they have no boost control issues?
It just seems strange that if my wastegate is just a little too small that the symptom would be uncontrollable boost rise (with the throttle plate wide open) within a few hundred RPM.

David Floyd

I have run a 35mm Tial on my 2.7 for many years now with rock solid boost control, first with a black **** and now with a Profec B

Paulyy

What spring do you have in it?
run this little test and it'll tell you that your wastegate it so small.

take of the MBC and block now 2 open hose ends. go for a drive and if it holds the boost your spring is set as, the wastegate isnt the problem.

Duke

I've tuned a 3.0l with Tial 38mm and only time I experienced boost spikes was sometimes during fast shifts, but it could probably be tuned out with the boost controller for 95% of the occasions. Did not experience boost creep, even with less than 15 psi.

So not sure the wastegate is whole truth in your situation. Perhaps try with a softer spring first?

TurboTommy

Well, I did the test; took the boost control system out of the loop and ran only the spring pressure of the wastegate.
Still major boost creep; would go to oblivion if I didn't lift.

Duke

But I assume you had a pressure line attached from turbo outlet to wastegate side port (in case of tial)?

kahlveen

Yes. You need to have manifold pressure going to the side port. With no lines attached, the only opening force is the exhaust pressure on the wastegate valve, and like you said, it'll boost to oblivion if you let it! With manifold pressure to the side port, you should only boost to approx. the value that your spring is rated.

Paulyy

yeah do check if its connected properly,

What spring does it have?

TurboTommy

Yes, of course; boost pressure from charge pipe banjo directly to top of LR wastegate in single port mode.
Bench testing the gate; cracks open at 9 psi, and takes about 14 - 15 psi to fully open at full valve travel.

Duke

Something else is up, it's definately not the wastegate size that's the cause of the large boost creep.

Paulyy

I have the feeling the spring is to stiff. Duke's right, defently not the wastegate size.