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]

Many thanks, Tony. As it turns out, I was able to find the QSB6.7 turbo flange inner diameter spec on your Cummins Engine drawings page. The turbo exhaust flange on this engine has a 3.5″ inner diameter which turns out to be larger to accommodate the higher HP versions (425, 480, 550). The elbow flange inner diameter is only 3″ so I will need to get this mismatch corrected.

[Tony Athens]

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

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

[bdunigan]

Thanks, Steve, but my question is not about wet versus dry risers. It is about the Cummins exhaust flange and the variances (if any) between the QSB 5.9, 6.7, QSC 8.3 and QSM 11. Seaboard sells a SMX replacement for the Cummins that ‘fits’ all of these engines. However, I have read elsewhere that the gaskets are different between these engines which implies that the flanges are different. I am trying to determine if there are variances especially between the 5.9 and 6.7.

[Steve Lewis]

Here is the real reason to get rid of the wet elbows and have a new dry riser setups fabricated. I am in the process of buying a Sea Ray 460 Sundancer that has DTF wet elbows. I am in fresh water so I have a little flexibility. When the heads are replaced on the 480CE’s that this boat has we will be able to assess how far along they are in their lives.

https://www.sbmar.com/articles/marine-exhaust-risers-that-are-doomed-to-fail/

In salt water the clock is ticking fast!

[Author]

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