Cummins 250

[Albin284me]

Anyone know if Albin ever corrected this issue on the production line?

[Sisu22]

With regards to cruise speed we have a four bladed prop and at 2,600 we are hitting about 21 knots . Back down at 2200 we are at about 14-15 and 24 around 16-17. No idea on fuel burn numbers because I don't have a FloScan.

[Jakeh223]

I know this thread is very old, but my questions are directly related to this thread. recently got into a 1995 28 te with the Cummins 250. It has and still needs some work but I’m particularly interested in the speed and fuel efficiency.

I see Nancy used to have a 28te with a 250 and was getting really good results. Cruise in the upper teens to 20 (knots) and fuel burn around 5gph. I am trying to find that balance in performance.

I am running a 19x21.8 prop and I don’t think it has any cupping. The previous owner was having smoking issues and was messing with having props re pitched. I believe his smoking issue was due to a turbo (and elbow) which I had to replace. It was completely stuck when I got it and I suspect it was starting to seize up when he was messing with the props.

Anyway I get 2875 rpm now with 4 adults and 2 kids, no gear. I’m only getting about 21mph (18 kts) at this load and rpm. At 2250 to 2300 it seems to want to settle in around 15-16 mph which seems a bit slow to me. I’m hoping to get the cruise speed up a bit. I no longer have smoke issues besides a bit of black “getting over the hump” and the massive plume on a cold start .

It seems to spin a little fast to me. I believe I want to be in the 2700-2750 range with a lighter load.

It appears from Nancy’s previous posts the 28 te with a 250 did well with an 18x21 with a #5 cup or 18x20 #3.

Just looking to see if anyone has any tips on what to try from here. I am not sure what my transmission ratio is but guessing it might be different given the higher pitch but higher rpm than what I’m seeing. Maybe the cup is the key?

[MerryKate]

Jake -

We ordered our 1996 28TE with the 6BTA250 Cummins, vs. the 315hp option at the time. For reference, our setup is a 1.4:1 gear, 3-blade 18x20.75 light cup (prop scanned). Cruise is ~17kts at 2300rpm and ~22+ WOT at 2700rpm vs. 2600 rated. It does well and is economical, but as others commented here, the 28TEs are just a bit more lively with 300-315 hp. But then you're into raw water-cooled aftercoolers, etc. Not being a speed freak, it's a good compromise for me. And these were basically the same blocks tuned up to 370hp in later years, so there seems to be some margin pushing the lower hp rated versions assuming your cooling system is up to it. But.... consider if you really want to:

In my experience, these hulls take about 200hp to cruise around 16-18 kts with a clean bottom and not heavily loaded down (and they are sensitive to weight). At 20 hp per gal/hr, this is an honest 10 gal/hr, regardless of the size of the engine. That's just physics: no 28 is going to cruise in the mid-teens at 5 gal/hr. Propped a little on the aggressive side like mine, the 250 will cruise there, but will be running consistently at 80+% load, vs. 65-70% for the higher hp options.

But the prop drives the boat, not the engine. Prop diameter and pitch (cupping to some extent), as well as blade area - number and size of blades - all have to be balanced. And gear ratio is a critical factor that often goes unreported (that 250 pushing a 4-blade 18x21 must have had a steep gear reduction!). You definitely want to “prop” (ie.sum all these factors) to achieve 100-200rpm over rated, 200 being much better. If your tach is accurate (be very sure!!), fully-loaded WOT of 2875 is very conservative against the 2600 rpm spec and should make for easy use of an already 30 yr old motor. She may have some performance to give back if it's really worth it to you, but on the other hand the previous owner may have already discovered the best solution to a potentially expensive problem for you. A good prop shop supplied with lots of accurate data can help frame your options.

These are great boats and great motors, and spring is here! Enjoy!

[Jakeh223]

Thank you for the reply and the insight MerryKate. I will see if I can determine what gear ratio I have. It does seem like it must be quite different to be spinning nearly 2900 with the 19x22 4 blade. I will also look at the other prop when I gar a chance to see what it was. It appears to have been used at one point.
I plan to put some hours on it this spring and see how it does on fuel economy. At the end of the day I guess I’d rather have the longevity over a couple of extra kts at cruise with a risk of early demise.

[MerryKate]

Hey Jake, re-reading your post I just realized the speeds you were giving were in mph, not kts(!!) Apologies, but that does seem quite a bit less than you should be getting out of this motor. One thing you can test is rev the engine to WOT in NEUTRAL to check the governor rpm. If it's near what you're seeing under full load at WOT, you could have a lot of room to add in some pitch and increase your cruise and WOT speeds some and still have plenty of safety margin. All the same principles apply, but did'nt want to mislead you into being over-conservative. Checking with a good prop shop would still be a good idea and make sure your tach is accurate.

[Jakeh223]

I took a look at the boat today. The transmission is a Hurth 800 and the tag is marked 1.4. I assume that’s a 1.4 gear ratio.
Also ran the engine up to WOT in neutral after warming up at the dock. It hit just shy of 3000 rpm. So good to know I’m not hitting the governer. Thanks for the idea on checking.

My 2nd prop turns out to be a 19x20 4 blade. Maybe I’ll talk to my prop shop locally and play with cupping on the 2nd prop or re pitching.

My only other thought is this boat is fitted with a trolling valve. No pressure gauge. But I’ve checked several times the valve is all the way closed, at least as closed as the lever can push it.