Turbo dyno dilemma

[Power Surge]

Got the turbo SHO on the dyno right now, and have an odd problem. Car is making 6 psi at 4500 rpms (wastegate is supposed to be 8psi) but after that boost drops down 2 psi by 6000. I tried blocking off the line to the bypass to make sure it wasn't opening, and I tried blocking off the line to the wategate, to see if it would give max boost.

At this point, I'm guessing the wastegate must not be fully seated and is bleeding exhaust off.

Anyone else have any ideas?

 

[I'll sho u]

what about a pressure/vacume leak in the intake somewhere?

 

[Power Surge]

what about a pressure/vacume leak in the intake somewhere?

It's possible, but I doubt it. Everything's been resealed on the upper intake and all, plus I didn't hear any kind of air leak or whistle during the pulls.

Also, it makes 6 psi at 4500, so I would think if there was an intake leak venting pressure, it should still make at least 6 psi up top.

 

[somedude_001]

did you plug the vent on the bottom of the throttle body?

you could disconnect the wastegate feed line and take your car for a ride. ease teh car up around 5-6K then tip in and see if your car is making full boost. with the line disconnected the boost will come on hard and fast so be cautious not to let it get super high.

my bet is on a big boost leak or even a exhaust leak before the turbo. check carfully. re tighten all of your clamps to ensure they didn't come loose on you like mine do acasioonaly.

 

[somedude_001]

just a thought but there is a vaccume line in the front of the intake just after the throttle body. is that disconnected? did you remove your charcol canister? is it possible that youy are boosting your gas tank and or charcol canister?

 

[Power Surge]

Bottom of the TB is plugged (old PCV line). The port on the intake after the TB (the old canister purge line) is plugged, I was actually using that port for the dyno's boost signal.

I did try taking the boost/vacuum line off the wastegate to see if boost went up, and it made zero difference.

 

[Power Surge]

Well, I just checked over the car. Not even the slightest hint of an exhaust leak. I then pulled the wastegate to visually inspect it. Didn't look like there was any sealing issue between the valve and seat, which is also verified with a simple water test. So the gate isn't leaking exhaust.

So now I know there's no exhaust leak, and the gate it sealed. And I tried a pull with the line off the gate, which should have made maximum turbo boost, and no change.

At this point, I am wondering if this turbo is just out of steam. It seems kind of drastic, but I guess it's possible. I am running a Holset HC-1, which is an early 90s Dodge turbo diesel unit. I know that they were not meant for high rpms, but they WERE meant for a motor with twice the displacement as the SHO, so I figured that might balance out.

So still open to suggestions at this point.

 

[somedude_001]

it really sounds like you have a boost leak.

are you blow through or draw throug? if you are draw through then you should be running extremely rich if it is leaking. Unless it was leaking the whole time and you tuned the car to it like that.

how is the filter before the turbo? is it small? if you remove it and run open turbo is ther any change? could the intercooler be damaged and be causing a major air restriction?

your theory on the turbo size works in my head too. those diese units are also setup to run a lot more than 10psi too so I wonder if changing to a different exhaust housing would help any if the turbo is infact the issue.

is the turbo getting suffecient oil? I know is sounds silly but if it isn't getting a good oil supply it could be slowing the turbo down... is it a ball bearing turbo? if it is are you running the proper oil restrictor so you arn't getting too much oil.

 

[Off Road SHO]

This is a tough one. Can you move your vacuum guage to a spot farther away from the throttle body? And plug the vapor purge port of course.

You might be blowing past the turbo's bushing/seal and into your crankcase.

Keep in mind that those old Dodges rarely went past 2200 rpm so at 4500rpms on a SHO you're pumping more air than the oil burner does at 2200. 2200 x 5.9 liters = 6490 liters for the diesel and 4500 x 3.0 = 6,750 liters for the SHO.

Might try the HC-35 or HC-40.


Tom

 

[Power Surge]

it really sounds like you have a boost leak.

are you blow through or draw throug? if you are draw through then you should be running extremely rich if it is leaking. Unless it was leaking the whole time and you tuned the car to it like that.

how is the filter before the turbo? is it small? if you remove it and run open turbo is ther any change? could the intercooler be damaged and be causing a major air restriction?

your theory on the turbo size works in my head too. those diese units are also setup to run a lot more than 10psi too so I wonder if changing to a different exhaust housing would help any if the turbo is infact the issue.

is the turbo getting suffecient oil? I know is sounds silly but if it isn't getting a good oil supply it could be slowing the turbo down... is it a ball bearing turbo? if it is are you running the proper oil restrictor so you arn't getting too much oil.

MAF is in the duct to the TB. The car was very rich on the first pull, but that was to be expected. I made it rich to start, and then the boost dropping off made it even more rich by the air not being there.

The inlet of the turbo is a 3" duct, with a 5" long x 4" wide cone style filter. I did not try taking it off, but I can't see that being too small for not even 250whp.

Oil wise, it's a bushed turbo, and I have a feed restrictor on it. I understand what you are saying with this one, but I really don't think that's it. The boost curve is just too repeatable.

 

[NotSoSlowSHO]

What are you using for tuning?

 

[Power Surge]

What are you using for tuning?

SCT, why?

 

[SeanMc]

Kinda OT, but what SCT product do you use? I don't think Livewire supports EEC-IV right?

 

[Power Surge]

Kinda OT, but what SCT product do you use? I don't think Livewire supports EEC-IV right?

Only thing you can use on EEC4 is a chip.

 

[Power Surge]

Here's the last dyno, for those who want to see. You can see it starts off like a normal turbo SHO dyno, boost goes to about 6 psi, then at 4500 boost drops off along with power.



BTW, I don't think it's the turbo not being able to support it. I went back and found all the old searches from when I was looking for a turbo, and the HC1 is being used by tons of people, some of them making 25+ psi. These turbos are used sucessfully on everything from 4 bangers to small blocks.

 

[Lightning]

I know you said that your intake has been resealed, but it seems like a strange coincidence that your boost levels off just after the secondaries open. To me, this points to an intake leak on the secondaries after the butterflies...

Are you really sure that intake is all nice and sealed up?

 

[Power Surge]

I know you said that your intake has been resealed, but it seems like a strange coincidence that your boost levels off just after the secondaries open. To me, this points to an intake leak on the secondaries after the butterflies...

Are you really sure that intake is all nice and sealed up?

Well, if you look at the dyno, it doesn't really happen till almost 1000 rpms after the secondaries open.

 

[Lightning]

The drop off, yes, 1000 rpm, but the beginning of the plateau occurs there around 4375, only ~ 250 rpm after opening.

I can understand the dip when the secondaries are first opening (larger area to pressurize), but why the small peak and valley immediately following that?

What it looks like to my untrained eye is that the turbo is starting to build more boost following the secondaries opening at between 4250 and 4350 but then it loses pressure briefly before recovering to the same level but at 4650.

It just seems to me that dip 4475 shouldn't exist at all, but should be a build in boost instead.


Like I say, it just seems suspicious to me that all this is happening so closely after the secondaries opening.

 

[Sho Amo]

sal, have you checked to see if your secondaries are opening correctly? just look at the plate next to the solenoid and with you hand rev it up to 4 grand and the tab should move.

i was thinking you are experiencing blowby when boost gets past 6 psi, but if i remember right you said in the other thread about the crankcase vents that your compression checks came out good.

where is your maf and is it a blow thru?

 

[Sho Amo]

on second thought maybe a stuck exhaust valve?