[NIVEK]

Hi All.
I am new and looking at acquiring a 3500 Express with diesels. I am interested in the difference in fuel burn (mpg) between the 370 hp (6BTA5.9) and 450 hp (6CTA8.3) Cummins. I found one thread indicating 1.2 mpg for the 370s and wonder how the 450s compare? Based on Cummins curves, the 450 is much higher at comparable RPM which makes sense but I am really interested in mpg. Any information, wisdom etc. would be welcome regarding the 2 engines. This looks like a great forum with a wealth of information.
Thanks!

[Crystal Bay Ad Man]

I can't comment on the file burn just to say it seems to have much more range. What I can tell you is that I looked at a very lightly used 35 Express in Sturgeon Bay Wisconsin this spring, real nice boat and seemed to be priced really well. Twin diesels and the cabin looked like it was never used. The boat was just to big for my needs, I ended up with a 3100 also from Door County, love the boat.

[jmk]

Both motors, when functioning properly, will deliver the same HP for the same rate of fuel burn. The boat with the larger 8.3 liter engines carries about 1000 lbs more total engine weight in the boat, which will reduce fuel economy. So if all other factors are equal, that boat will be less fuel efficient.

Cummins CTA are physically larger than BTA motors, and in a boat this size access around them may be tight.

BTA motors are enough for this hull. Advantage of the CTA motors is they will have a very easy life pushing this boat.

[RickT]

I have a beautiful blue hull 2001 35' Express for sale with the 370 HP B's. They get one mile per gallon at cruise but we get 3 miles per gallon for most of our cruising running 6 to 7 knots at around 1,000 to 1,100 where we are comfortable
email me at rick_traskos@prodigy.net for more info. Happy to deliver it anywhere on the east coast or great lakes.
3500 Express - Diesel
Cummins 370B (370 HP)
PERFORMANCE REPORT
Location: Holland, MI - Lake Michigan
Weather: Calm / Wind 10-15 kts out of South
Water / Air Temp: 57 / 75
Propeller: 24 x 26 - 3 blade Nibral Mich #7 cup
Gear Ratio: Hurth 800 v 2.00:1
Fuel Capacity: 354 gallons
Fuel/Water/Waste: 100%/100%/0%
People on Board: 3 people
Gear on Board: Approximately 400 lbs.
PERFORMANCE:
Acceleration: 14.25 seconds to 2800 RPM
Optimum Cruise Speed: 25.1 / 31.1 MPH
Range at Optimum Cruise: 315 / 299 Statute Miles
RPM MPH Knots GPH MPG dB,A Trim Angle Estimated Range
(Statue Miles)
590 5.7 4.9 1.9 3.00 66 1.0 956
1000 7.3 6.3 2.5 2.95 73 1.2 940
1500 10.3 8.9 6.5 1.59 80 4.5 508
2000 15.1 13.1 20.4 0.74 83 7.5 236
2200 19.4 16.9 22.7 0.86 84 8.9 273
2400 25.1 21.8 25.4 0.99 84 6.9 315
2600 27.2 23.6 29.0 0.94 84 5.6 299
2800 31.1 27.0 33.2 0.94 85 5.1 299
3000 32.5 28.2 39.3 0.83 86 4.7 263
3084 P 33.8 29.3 41.8 0.81 87 4.3 257

[Chris Burkard]

I sent Nivek performance reports for both the 370Bs and the 450Cs. According to the Tiara performance reports, the larger C series engines are slightly more fuel efficient at planning cruise speeds. This is likely do to loading. The 450Cs are under a light load when planning and the 370Bs are under more load and require more fuel burn to operate at those speeds. Nothing wrong with the Bs, just more efficient with the Cs.

[NIVEK]

Thanks all. Great information. It appears the Cs are no worse, and perhaps better, than the Bs in terms of fuel economy based on the Tiara test results. Not exactly all apples given fuel and water loads but it seems the Cs are very similar and or slightly better considering this. C width is only 1" more and height is 2" less so seems access would be comparable (although they are 6" longer but not sure this is a big impact...thoughts?). Regardless, both engines have a great reputation so hard to go wrong either way.

[trit21]

With all that considered, if you have a choice between 2 boats, one with 6bta's and the other with 6cta's, I think the consideration should be given to the boat that has the best maintenance records. These engines have to be taken care of and if they are not, then you will spend a lot of money getting them fixed. Making sure they reach over rated RPM should be #1 on the list.