26 ft Cummins 6bt

Herman Van Boven

New Member
Jun 8, 2021
4
0
I have a 6bt engine and only get 2400 rpm and black smoke.Zf transmission 1.2 1 17X 22 prop. 4 blade
i believe i am over proped but what size prop should i get.
thanks in advance Herman
 

Mistress

Moderator
Staff member
Supporting Captain
Jan 22, 2005
7,530
245
San Jose, CA
Black smoke typically points to turbo or intake air filter. But achieving 2400 would tend to negate the turbo aspect. When my turbo locked up it was thick clouds of black and wouldn't climb above about 1500 rpm underway.

But that does sound like a LOT of prop.

Factory on 1:1 was 16x17. Mine came (from PO) as 16 x 16 and I'm actually running a 16 x 15 to reduce my trolling speed.

So back to factory: 17"' x 1.2 = 20 and an inch bigger wheel. I'd think 17" x 19 would be about right.
 

Kjorah

Active Member
May 6, 2007
37
9
Florida
I have the same bt6 and zf 1:21 running 17-17 prop. 2400 rpm is about max for that engine before you start over heating. Be careful pushing that hard head cracks easy also manifold and turbo. I done that twice. 2100 -2200 has been safe for me. black smoke is to much fuel check pump and or injectors.
 

Mistress

Moderator
Staff member
Supporting Captain
Jan 22, 2005
7,530
245
San Jose, CA
I have the same bt6 and zf 1:21 running 17-17 prop. 2400 rpm is about max for that engine before you start over heating. Be careful pushing that hard head cracks easy also manifold and turbo. I done that twice. 2100 -2200 has been safe for me. black smoke is to much fuel check pump and or injectors.
You shouldn't overheat (water or EGT) at 2400 if properly propped. That engine is spec'd to run on the pins (2600) for like 8 hours out of 9.
 

Tuloko77

Well-Known Member
Supporting Captain
Sep 12, 2020
87
13
Mammoth Lakes
For what it’s worth, I’ve got the same engine and an old Michigan 17 x 17. I’m maxing out at 2,550 rpm’s, and plan to get a new prop in the not too far future. I have some minor pitting on the prop and have bottom paint. I’m guessing without that, I’d be able to achieve 2,600 or more, what the engine is spec’d to do.
 

Mistress

Moderator
Staff member
Supporting Captain
Jan 22, 2005
7,530
245
San Jose, CA
For what it’s worth, I’ve got the same engine and an old Michigan 17 x 17. I’m maxing out at 2,550 rpm’s, and plan to get a new prop in the not too far future. I have some minor pitting on the prop and have bottom paint. I’m guessing without that, I’d be able to achieve 2,600 or more, what the engine is spec’d to do.
What's it reach in neutral?
 


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