QSB 6.7 exhaust elbow flange questions

[bdunigan]

My tech is performing a 500 hr service on my twin QSB6.7 units installed in a 13 Sabre 42SE and suspects the exhaust elbows (DeAngelo) need replacing. He recently replaced the elbows on a similar Sabre and noticed the inner diameter of the elbow flange was slightly smaller than the inner diameter of the turbo exhaust flange. He didn’t like this fact and expected both inner diameters to be the same. When he used a QSB5.9 gasket, it matched the replacement elbow flange but was too small for the 6.7 turbo flange. When he used a QSB 6.7 gasket, it matched the 6.7 turbo flange but was a bit large for the elbow flange. I have read that the Cummins exhaust flange is the same for the 5.9, 6.7, 8.3, and 11 engines. If true, is it normal for the inner diameters of the elbow and turbo flanges to be slightly different or should they ‘match’ (for even flow)? I see SB sells a SMX flange that is 2.5mm larger than stock and has a ‘beveled’ flange for improved flow. Are these changes to improve inner diameter differences when using a Cummins flange? Thanks in advance.

Topic

[bdunigan]

Tony, thanks for the quick reply. I am amazed you are ‘online’ on a Sunday evening! Wow!

I will run the ‘out to sea’ test you have prescribed sometime this week and report back.

I will describe my typical usage as follows: My cruising area is the Chesapeake Bay and the ICW down to Hilton Head, SC. The majority the time, seas are less than 1′. Rarely do I see anything greater than 1.5′-2′ seas. My runs are ‘continuous’, point to point, no stopping, no floating/fishing….just cruising to that day’s destination. I run at 65-75% load and no greater than 29gph. I will occasionally go to WOT for testing purposes. As a rule, I come of plane very slowly. There have been perhaps two occasions over the last 300 hours where I had to pull power quickly. Only once have I run in serious trailing seas of 2′-3′ and was at cruise power during the run. Hope this helps.

No response required until I runtime ‘out to sea’ test.

Again, many thanks!!

[Tony Athens]

Pick your typical weather that you go out to “sea” and let’s make a trip………..Make your “test system” safe for the trip.. Once “out to sea” and you do what you do ( I am assuming you shut down and “drift” or ?? ( what I call rockin’ & rolling” ), hook it back up and lets see what is going on… Be sure you are at your typical “vessel weight” for this trip..

It’s super obvious that seawater has been getting into your turbos for years when you “are not” running the engines eating away at the cast iron housings….

We need to figure out when/how it is happening

We are now into the discovery mode of “forensic files”

I am curious———What do you do when you going out to sea?

[bdunigan]

It looks like I did delete a post although I am having some trouble with the system. Here is the deleted post….

“What exactly (some engine symptom or ?) brought on all the questions and concerns about the exhaust flange connection ID?”

During a 500hr service, my tech identified leaking exhaust elbows. My Sabre 42 is a 2013. He had recently replace an exhaust elbow on 2014 Sabre 42 (same engines as mine…QSB6.7 380hp). The replacement elbow was ordered from DeAngelo who supplied the originals to Sabre. My tech noticed that the elbow gasket that came with the replacement elbow was smaller than the flange on the turbo. The elbow gasket was 3″ ID and the turbo flange was 3.5″ ID. He found this odd but completed the repair using a QSB6.7 3.5″ gasket

My tech mentioned this discrepancy to me when he identified my elbow issues. I contacted Sabre who sent me the drawings for the original elbows. These drawings and DeAngelo confirmed the original specs from Sabre and Cummins called for a 3″ ID elbow flange. I questioned Sabre who stated that the sea trial data for my boat was ‘within spec’. IOW, the exhaust back pressure was acceptable even though the elbow flange was smaller than the turbo flange. Note: my Sabre 42 is the first with the 6.7 380hp engines. The prior 42s had the 5.9 380hp engines which I believe have a 3″ ID turbo.

So Sabre and Cummins put a 3″ID exhaust flange against a 3.5″ turbo flange. By my calculation, the area of a 3.5″ circle is 9.62 sq in. The area of a 3″ circle is 7.1 sq in. In essence, that equates to a 2.52 sq in road block of the exhaust exiting the turbo or basically a 25% restriction. Maybe this doesn’t matter to a 6.7 380hp unit. Maybe the 3.5″ turbo was designed more for the 425/480/550 hp 6.7 units. I really don’t know.

I had DeAngelo make the replacement elbows with a 3.5″ flange so they matched the turbo flanges.

I have the engineering drawings for the original elbow from Sabre if you want to see them.

Note: The picture of my turbo was taken immediately after the elbow was removed. There is gasket material still on the turbo flange. As you can see, the gasket is the graphite version. We installed the metal version during our repair.

[bdunigan]

It looks like I did delete a post inadvertently. Here it is….

“What exactly (some engine symptom or ?) brought on all the questions and concerns about the exhaust flange connection ID?”

During a 500hr service, my tech identified leaking exhaust elbows. My Sabre 42 is a 2013. He had recently replace an exhaust elbow on 2014 Sabre 42 (same engines as mine…QSB6.7 380hp). The replacement elbow was ordered from DeAngelo who supplied the originals to Sabre. My tech noticed that the elbow gasket that came with the replacement elbow was smaller than the flange on the turbo. The elbow gasket was 3″ ID and the turbo flange was 3.5″ ID. He found this odd but completed the repair using a QSB6.7 3.5″ gasket

My tech mentioned this discrepancy to me when he identified my elbow issues. I contacted Sabre who sent me the drawings for the original elbows. These drawings and DeAngelo confirmed the original specs from Sabre and Cummins called for a 3″ ID elbow flange. I questioned Sabre who stated that the sea trial data for my boat was ‘within spec’. IOW, the exhaust back pressure was acceptable even though the elbow flange was smaller than the turbo flange. Note: my Sabre 42 is the first with the 6.7 380hp engines. The prior 42s had the 5.9 380hp engines which I believe have a 3″ ID turbo.

So Sabre and Cummins put a 3″ID exhaust flange against a 3.5″ turbo flange. By my calculation, the area of a 3.5″ circle is 9.62 sq in. The area of a 3″ circle is 7.1 sq in. In essence, that equates to a 2.52 sq in road block of the exhaust exiting the turbo or basically a 25% restriction. Maybe this doesn’t matter to a 6.7 380hp unit. Maybe the 3.5″ turbo was designed more for the 425/480/550 hp 6.7 units. I really don’t know.

I had DeAngelo make the replacement elbows with a 3.5″ flange so they matched the turbo flanges.

I have the engineering drawings for the original elbow from Sabre if you want to see them.

Note: The picture of my turbo was taken immediately after the elbow was removed. There is gasket material still on the turbo flange. As you can see, the gasket is the graphite version. We installed the metal version during our repair.

[bdunigan]

I completed the ‘water level’ test as described above. This test was ‘at the dock’. Attached are two photos. The measurement from the bottom of the elbow to the water level in the clear tube is 12″ which I understand is a ‘minimum’ requirement. This doesn’t give me a lot of faith in the design. Comments?

[Tony Athens]

Do not dwell on exhaust pressure…This IS NOT your issue……………… Your engine is going to die a nasty death if you continue along your currert path..

If your turbo was not eaten out from years of saltwater ingestion, you’d see over 33 PSI of boost at WOT……….

Did you delete a post ?

[bdunigan]

I agree that the Sabre/Cummins logic is flawed and that their back pressure measurements were lowered by the restriction. In fact, during our sea trial after installing the new 3.5″ elbows, turbo boost at 3000rpm was 2-4 psi higher. At WOT (3050 rpm), turbo psi hit 29 psi which is right were the actuators start to open. In past tests, the WOT turbo psi was closer to 25-26 psi. While I didn’t experience a significant increase in WOT rpm (maybe 20 rpm), the boat felt better.

Should I remeasure exhaust back pressure to ensure it is still below spec? I understand that 5 in hg is maximum. During the original sea trial by Sabre in 2013 with the smaller elbow flanges, they saw 3.3″ port and 2.8″ stbd.

Do you think removing the exhaust restriction would cause exhaust back pressure to exceed 5″?

[Tony Athens]

This is just an IMO based on more faulty information you are being fed..

Use common sense and think about this..

Understand———————————Exhaust pressure is MEASURED after the restricted gasket/ flange ID or what ever.. The more restrictive the flange or gasket is, the LOWER the pressure will be…………………..AGAIN, Think about it….

I am not saying you have an issue, I just want YOU to understand that the way you are be fed info is totally “ass backwards”……….

Take it to a an extreme if this helps– Put a gasket in there with a 2” ID–What do you think would happen to the “measured exhaust pressure” that is measured down stream of the very restrictive gasket?? As to what the ENGINE is SEEING inside the turbo outlet before the restriction is a totally different number and the one the really matters……………………But this for a different topic..

[bdunigan]

“What exactly (some engine symptom or ?) brought on all the questions and concerns about the exhaust flange connection ID?”

During a 500hr service, my tech identified leaking exhaust elbows. My Sabre 42 is a 2013. He had recently replace an exhaust elbow on 2014 Sabre 42 (same engines as mine…QSB6.7 360hp). The replacement elbow was ordered from DeAngelo who supplied the originals to Sabre. My tech noticed that the elbow gasket that came with the replacement elbow was smaller than the flange on the turbo. The elbow gasket was 3″ ID and the turbo flange was 3.5″ ID. He found this odd but completed the repair using a QSB6.7 3.5″ gasket

My tech mentioned this discrepancy to me when he identified my elbow issues. I contacted Sabre who sent me the drawings for the original elbows. These drawings and DeAngelo confirmed the original specs from Sabre and Cummins called for a 3″ ID elbow flange. I questioned Sabre who stated that the sea trial data for my boat was ‘within spec’. IOW, the exhaust back pressure was acceptable even though the elbow flange was smaller than the turbo flange. Note: my Sabre 42 is the first with the 6.7 380hp engines. The prior 42s had the 5.9 380hp engines which I believe have a 3″ ID turbo.

So Sabre and Cummins put a 3″ID exhaust flange against a 3.5″ turbo flange. By my calculation, the area of a 3.5″ circle is 9.62 sq in. The area of a 3″ circle is 7.1 sq in. In essence, that equates to a 2.52 sq in road block of the exhaust exiting the turbo or basically a 25% restriction. Maybe this doesn’t matter to a 6.7 380hp unit. Maybe the 3.5″ turbo was designed more for the 425/480/550 hp 6.7 units. I really don’t know.

I had DeAngelo make the replacement elbows with a 3.5″ flange so they matched the turbo flanges.

I have the engineering drawings for the original elbow from Sabre if you want to see them.

Note: The picture of my turbo was taken immediately after the elbow was removed. There is gasket material still on the turbo flange. As you can see, the gasket is the graphite version. We installed the metal version during our repair.

[Tony Athens]

Another question that I would like a answer to that makes some kind of sense.. I purposely stayed out of this as to the ID measurement part because it was a very “ODD” thread for a typical boat owner to be concerned about.

What exactly (some engine symptom or ?) brought on all the questions and concerns about the exhaust flange connection ID?

I’m thinking that this is going to get quite “serious” before the dust settles, and you need to accurately document everything very well..

[bdunigan]

Thank you, Tony, for your reply and expertise. I am pretty discouraged by your observations. It isn’t the techs per se as what you see is the original design and installation by Sabre Yachts in partnership with Cummins Northeast. There isn’t enough clearance above these motors to install anything but the elbows you see (IMHO). In other words, every Sabre 42 is built this way. Ugh!! I will execute the water level test via the cap and hose you recommend and report back. Again, many thanks.

[Tony Athens]

I looked closer at the inside of your turbo……………….

Your exhaust system/riser /design is a total joke and who ever is guiding you in the figure out what the issue is” has no business on your vessel, or any vessel. Also, there is better than a 50-50 chance your valves have serious damage to them because of this.. Thread lightly from here as to even running your engine. Drop a valve and the Number to fix will be 5X+.

If you are in denial of what has been going on for years, and keep listening to your current techs, mechanics or ??, I cannot help..

Why I asked about your Groco? Buy a bronze cap for it. Install a fitting(s) on the top and then a piece of clear 3/8″ hose and take it up to the ceiling. Let’s really “SEE” where your water like really is sitting at the dock engine off, and then see where it is “rocking and rolling” at sea, engine off…

[bdunigan]

Yes, it is a Groco ARC 2000s. What do you think of the exhaust elbow pics?

[Tony Athens]

Is this the sea strainer for the engine?

Regardless, read the label as to the size.. It is a GROCO ARG ????

[bdunigan]

Hope these pics suffice. Zeus pod boat. Besides the sea water cooling hose from the heat exchanger (pictured), there is a second hose on the backside of the elbow that takes part of the cooling water supplied by the HE and feeds it to the trans coolers mounted on the zeus pods. As I am sure you know, the elbows connect to FRP tubes that run down to the pods. I would estimate the vertical drop from the elbows to the pods at 18″. There is an exhaust bypass built into the FRP tubes that goes to lift mufflers and then out the transom.

[Tony Athens]

Hire a new tech he does not belong in this business……………..100% you are and have been feeding your turbo/engine saltwater for quite some time ( years??) .Internal valve damage is very possible based on what I see here.

Understand, that is 100%——– no iffs, no ands or buts about it..

You need to redesign your exhaust system……….Let’s see what you have from a few feet away from a few angles and perspectives—————————- No close-ups

IMO, I would not run you engine any more until this is fixed.. Your call..

What a Marine Diesel Turbo should look like when Inspected

[bdunigan]

The new 3.5″ ID exhaust elbows are now installed. A sea trial showed very little difference in performance over past results. The boat may have gained 20 rpm at WOT. Otherwise, similar loads and fuel burn to the past. I suspect the QSB6.7 3.5″ turbo outlet is intended for the higher power 425/480/550 units. I did get excessive carbon build up in the turbo exhaust outlet which I attribute to the restriction of the 3″ exhaust flange and I certainly feel the system is better off with matched flanges. Turbos were removed and cleaned as well.

[bdunigan]

Tony, I will once the elbows are out. I had a bit of a tiff with Sabre yesterday who said it was not a mistake on their part to put a 3″ exhaust flange behind a 3.5″ turbo exhaust opening. I later spoke to a Cummins engineer who said he had no trouble if I had the new flange enlarged to 3.5″. I am ordering the new elbows and will post pics once the job begins. Many thanks.

[Tony Athens]

One more time:

Post good pictures of EXACTY what your “tech” sees, or now YOU SEE, and seems to have issues with……………………………………………. Everything..

That’s the only way I or anyone could comment properly..

[bdunigan]

The plot thickens. I now know that I have a 3.5″ turbo exhaust flange and a 3″ exhaust elbow flange. The boatbuilder did this and Cummins signed off on this (after extensive sea trials). That said, it makes NO sense to me that Cummins would bless an exhaust elbow flange that is 1/2″ smaller than the turbo exhaust outlet inner diameter. The boatbuilder is NOT cooperating and says that as long as the sea trial back pressure specs met Cummins requirements they are fine with this restriction (which it did). My tech and DeAngelo Marine (who made the elbow) both say the two should match. I need two new elbows and need to figure out what inner diameter to use for the elbow….3″ (leave the restriction) or 3.5″(match the turbo).

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