Compound turbo problems

[Strokinbronco]

Okay guys here we go. I have a 1993 bronco with a 96' 7.3 running compounds, it's an s369 / gt5523 (88mm) with 400/200s for fuel. My issue is that I'm having a hard time spooling while daily driving, the setup won't even begin building boost until 2500rpm and the most boost I've gotten out of it is 60psi. That's less that what I've made with the s369 as a single. When I built the setup I made a bunch of changes to the truck, went from 38s to 35s but kept the 4.30 gears, also went from a low stall converter to a stock stall converter thinking it would help to light the chargers. Also the truck is relatively light at 5200lbs full of fuel. My intuition is telling me that the truck may be over-geared and not seeing enough load to spool the turbos but to be honest I'm kind of stuck. Any insight on the situation is appreciated and all opinions welcome, however I do ask that you refrain from asking "why put a 7.3 in a bronco, you can't tow with it" I did it cause I wanted to and that's all that matters.

 

[Powerstroke Cowboy]

Did you get tired of Facebook?? maybe I got the wrong guy?

I will not knock the 7.3 in a bronco. That happens to be on my bucket list.

What size exhaust housings do you have on the turbos?

Do you have a way to read backpresure before the hp turbo and between the hp and lp turbo?? If so. What's it showing?

 

[Strokinbronco]

To much bs on the book lol I need actual information and not "my buddy did this" kinda stuff lol. The 369 has a .91 housing and the gt55 has a 1.23 housing. I only monitor overall ebp and what's really throwing me off is that it'll make 10psi ebp before it makes any boost but after that it's been 1:1 all the way to 60psi. That being said even locked in od it's not building boost until 2400-2500 rpm

 

[Tiha]

I have a powerstroke in a bronco and I tow plenty. Everyone has an opinion. I just avoid everyone.

Are you blowing a lot of smoke below 2500 rpm?

 

[6.0 Tech]

Have you checked for boost leaks? If you’re building a decent amount of back pressure before the boost decides to do anything, you could have a boost leak. Would also explain the low total boost number.


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[Powerstroke Cowboy]

To much bs on the book lol I need actual information and not "my buddy did this" kinda stuff lol. The 369 has a .91 housing and the gt55 has a 1.23 housing. I only monitor overall ebp and what's really throwing me off is that it'll make 10psi ebp before it makes any boost but after that it's been 1:1 all the way to 60psi. That being said even locked in od it's not building boost until 2400-2500 rpm

I can see why you are being thrown for a loop. That by all rights should be a fast spooling setup.

I am sure you have checked for boost leaks already. But man it sounds like you could have a healthy boost leak.

This next thing might fly in the face of conventional thinking. Have you tried a bigger housing on the s369?

How much of the 60 psi is the gt55 making vs the s369?

 

[Strokinbronco]

I've searched for leaks everywhere! That was my initial though but there are none to be found. I haven't yet tried a bigger housing on the s369, I have a 1.10ar housing for it but was reluctant to swap it over until I figure out what the root cause was for the lagginess. I didn't want to make an already bad situation worse confusing myself in the process. I grabbed a screenshot of one of the pulls I made and at 50psi total the gt55 is making 35psi, hopefully it'll let me attach it cause it also shows my ebp gauge. For what it's worth the ebp was only 45psi at 50psi of boost so at least it's better than 1:1. The top gauge is overall boost, the one next to the hydra is the first stage (gt55), and the top gauge in the left is ebp

 

[BrewTown]

Let me start by saying I have no experience, just quite a bit of reading... Take that for what it's worth...
Do you have a gate around the 369? It almost sounds like that gate is bypassing the 369 at lower speeds, then both chargers are seeing enough to get moving at higher RPM. It's my understanding that at 60 PSI the atmo should be contributing roughly 20 PSI to the HP? I think.
Or is there an exhaust leak pre 369?

 

[Strokinbronco]

I do agree that the hp charger should be making more boost, but I'm positive the gate isn't the issue. It has 26lbs of spring pressure in it and is fed 100% manifold pressure to the dome so it's effectively pinned shut and non functional. Also I vented it to atmosphere because I was concerned about that very thing and the tube is still clean so I know it's not opening.

 

[Powerstroke Cowboy]

With your boost numbers, it shows the 369 is not spooling. The gt55 is doing all the boost but a few pounds of it. Something is keeping the s369 from spooling.

Even with a 1.10 housing the s369 should spool way before 2500.

Basically the gt55 is what's spooling at 2500rpm. That's why all the lag. The s369 is not spooling. Get that took.care of and you should have a fast spooling rig.

I still would like to know the exhaust pressure between the two turbos.

 

[psduser1]

Just another internet engineer, but back when I was looking into compounds, the general consensus was that the lp turbo was a big negative to spool the hp turbo.
As in, run the biggest single you were comfortable with, spoolwise, before sizing a lp turbo.
I haven't heard a single vendor recommend a 369 on a daily driver. They have all pushed towards the 364, and in a compound setup, I would agree. Then set your gate on the hp turbo at whatever bp you are comfortable with, and dump it to the 55. That setup should be capable of 100+ lbs of manifold pressure. In fact, you may have to gate the 55 to the atmosphere.
Admittedly, you should have enough fuel to light the 369, but the light weight and 4.30s are hurting you. Anyway to load the truck substantially?

 

[6.0 Tech]

What housing do you have on the 55 and what size turbine wheel? We have found in our 6.4 testing that it seems the low pressure is the restriction. Charlie has a good write up on it in the 6.4 section. We also found on a 7.3 we were testing compounds on that we gained some power by stepping the low pressure up from a 75 to an 80 and bumping the housing size on the low pressure which coincides with what we have seen on the 6.4. And I do agree with the hi pressure may be a tad on the large size. I found on my truck that by adding a low pressure turbo, spool slowed about 200-300 rpm, and this is with a vgt as a high pressure.

On the 6.4 we have found the high pressure is basically for off the line help and then the low pressure does the majority of the work. On a 60-65psi overall boost pull, we are seeing around 38-40 out of the low pressure. I’m aware apples to watermelons comparison, but I think the concept still applies.


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[Powerstroke Cowboy]

What housing do you have on the 55 and what size turbine wheel? We have found in our 6.4 testing that it seems the low pressure is the restriction.
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This is where I was going to head next. This is also why I wanted to know the exhaust pressure between the two turbos.

 

[Strokinbronco]

The 55 has a 111/100 turbine and a 1.23 housing, the compressor is a cast 88/123. I'm thinking that tomorrow I may pull the intermediate pipe and charge pipe off the atmos and see how the 369 spools as a single. That should tell me if the issue is with the 369 or elsewhere.

 

[Powerstroke Cowboy]

For what it's worth, there was a member on here that a had a GTP38R 66mm comp inducer with a 1.15 Turbine housing fed buy an 88mm gt55. I can't remember the turbine housing size on the gt55. He could see over 60 pounds of boost before 2000 rpms.

 

[psduser1]

This is how I did mine.

View attachment 61226

From back in 2011, on a 38r.

There are several guys back then, working from 38rs. I believe powerstrokecowboy is referencing "charles", specifically.

 

[Strokinbronco]

Okay so I pulled the intermediate pipe on the hot side and the interstage pipe on the cold side and ran it as a single s369. Same issue, no boost being built until about 2500 rpm. So atleast I've narrowed it down a little. May try throwing on that 1.10ar housing I have and see if anything changes

 

[Strokinbronco]

Well I dug a little deeper and found a pretty serious issue, something has made its way into the compressor wheel of the 369 so I'm just gonna assume that's part of my problem

 

[6.0 Tech]

Well I dug a little deeper and found a pretty serious issue, something has made its way into the compressor wheel of the 369 so I'm just gonna assume that's part of my problem

That’ll do it. Check the 55 as well, if something came apart in it it would do that. Also check the turbine wheel of the 69, see if it melted or something too. We’re the bearings bad, ie excessive play in it? And did it get the compressor cover?


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[Strokinbronco]

I checked the 55, it's fine. Also pulled the turbine housing and all is good on the hot side, the compressor cover has a few spots on it but they're all around the surge ring and look to be just cosmetic. The area where the compressor rides amazing looks untouched, the bearings are fine as well no shaft play at all. I had a separate shop weld a v band to the compressor housing of the 55 and even though I thought I cleaned it very well prior to install I must have missed something that didn't agree with the s369. Also double checked the wg dump and it looks as if it actually has been opening, it currently has 26lbs of spring pressure in it and is fed full boost to the dome so I'm not exactly sure how that's happening.