HP increase limitations

[setho]

I just bought a 1989 31 Grand Slam with 250 HP Cummins 6BTAs. Does anyone know how high I can increase the HP within the standard shaft configuration?

Thank you!

Seth

[Mistress]

Cummins could prolly tell you what the shafts are good for....or maybe Aquamet.

Also www.boatdiesel.com

Will cost $25 membership, but it's well worth the price of admission.

Do your homework before turning up the engines. It's not like trucks that seldom see full loads. Boats are always under a significant load...placing higher demands on cool air in, exhaust out and engine cooling. Are your 5.9's aftercooled? If not...there is very litle room to turn them up without aftercoolers.

Of course if you are successful at gaining much h.p....you'll need to reprop to make use of it. In my case...I already idle at 5.5 knots with a 16x17 wheel. More h.p....driving more prop... would make it even worse.

[setho]

Your right. I am in the trucking business where we regularly turn up diesels. Everyone I talked to said don't turn up my 6BTAs in a boat. I am content with them as is and hope to enjoy their reliability.

I have seen several places where people claim cruise speeds in the high 20s for 31 GSs - I find mine tops out at 26 to 27 knots at 2500 RPM and only cruises around 18 knots at 2100 RPMs. I do need to repaint the bottom and recondition the props (just bought the boat) will find out if that makes a big difference.

- Seth

[Mistress]

www.boatdiesel.com also has a shaft calculator. If Aquamet shafts, they can take gobs of horsepower.

I failed to see you have BTA's..so they are aftercooled. You might have a little room there. Ask on the website.

I do know that there's not much room on my 6BT as it gets cost prohibitive. the gut will hold up to it no problem if done right.

In contraast my truck with 24V Cummins is running ~100 hp over stock, but rarely has a chance to use it.

[setho]

Thanks you! boatdiesel.com is a great resource. I need to check on the manufacturer of my shafts.