GM 8.2L 502 385HP EFI versus Cummins 270-300 Diesel

[John Nardi]

Hi Guys....My old Cummins 504s are going to be removed from my 31 this week...Was hoping if that the vast audience of 31 owners on this site may be able to give a realistic comparison of running New GM 8.2l 502 CU IN either fuel injected versus carbureted and a Cummins 6BT say 250-300 HP. I have to be realistic as to my needs as this boat will strictly be a South Florida boat where my run to the Bahamas is only 60 nautical and I therefore am never more than say 30 nautical from help in case of a breakdown. I would like to think that I would put more than 250 hours on the boat per year, but from years of experience I believe 150-250 is more in the range. I will either be doing 1 of say 4-5 Bahamas trips a year or sword fishing 15 miles or so off the beach. I have had nothing but diesels for 30 years and am now just wondering when doing a complete repower, if modern gasoline engines may be appropriate particularly if injected (Even safer??) I am interested in performance stats, fuel burn at various speeds, safety stats and any other considerations you can offer....Thanks, all. John

[Navatech]

Have you seen these RTO's?!...

http://www.thehulltruth.com/parts-forum ... mmins.html

[Tony Meola]

John

If you have 1 1/2 inch shafts, the decision is somewhat easier since that is one upgrsde you will not need if you go diesel.

The prices on some of the Cummins recons have jumped. As I understand it, my 270 recons are now or expensive than the 315. It is due to demand. 270 After cooler is fresh water cooled so less upkeep.

I run light no tower or hardtop. At 2300 I am around 24 knots.

If you can with 150 hrs s year I vote diesel. Figure fuel consumption will be a lot less. Figure ,15 gallons an hour vs 25 and 23 to 25 knot cruise vs 19 knots you use about half the fuel. You save about 1500 gallons a year. That is about $3500 a year @ $2.50 gallon. In 10 years the engines pay for themselves. Go to 250hours a year and it is a no brainer.

[Carl]

In my mind, the amount of running your talking about, the fuel savings really come into play as does range of the boat.

Buying fuel in Bahamas, over having enough to get there, use boat, then get back on same tank is another consideration.

Last, put diesels in your 31 you'll have a 31 Bertram with diesels to sell if and when. They have value.

Put gas in...your selling a gas 31' boat boat...old 440's, 350's, 454's or 502's...its a gas 31.



Safety and reliability....
I do not see gas as being unsafe or less safe...I see gas requiring special precautions to maintain safety. Fume detectors are nice...but I always stick my head in the hole to check for gas fumes at the start of each trip, after fueling up. Check condition of fuel lines...Fire extinguishers are mounted where needed.
Diesel may not explode...but it sure does burn. I hear of more Turbo fires on diesel boats each year then all the gas boat explosions I have ever heard about in my lifetime. To add further...gas explosions always seemed to be negligence of operator...usually when leaving fuel dock.


Reliability- Old mechanical diesels in pretty good order always seemed to get back to dock and just ran and ran for years.
Today with all the new electronic crap, higher reving diesels, ...the motors run great, till they don't...that is both gas a diesel.
But overall, properly maintained, with basic spare parts they are pretty reliable and not something I'd choice one over the other for anymore.

Not a whole lot of info here...but its the scenario I play over in my head at times. I know for me...my hours do not come close to justifying the expense of going diesel at this time. Especially when my engine hours are mostly due to local trawling with short runs to and from fishing grounds...a couple beach, dock and dines. But several Bahama trips...that would tip my scale.

Good luck in whatever you choose,
Carl

[Stephan]

John-
I have old 454 Crusaders. They are the right engine for me,. simple to maintain - I go 17 kts when its rough; 20 kts when I'm just happy to be there and can go 25 kts if I would rather be somewhere else. I'm not sure that relative fuel burn, etc. is the way to look at it. I think it was UV who is quoted that the $$$ is in the steel. Maybe in this market a diesel boat gets a bid and the gas boat doesn't sell?
Good luck-
Stephan

[John F.]

I don't know anything about the Cummins 504s. I have seen people, here and elsewhere, really underestimate the cost of a gas to diesel repower. Its not just the motors--its the fuel system, exhaust, battery cabling, batteries, shafts, couplings, wheels, struts, raw water intakes and hoses, gauges, engine beds, air for the diesels to breathe. That sort of stuff. Being she's diesel now, maybe you're OK on that. To get a real picture of costs, I'd try to figure that out. If you're doing that many hours per year, and you're starting with diesels, I'd think diesels may be the right way to go. The Cummins 6btas at 210 hp may work with your current fuel/exhaust/shafts/etc., and will give you a cruise about equal or a little better than 454s (though not as fast as 502s).

I'd also want to know who is marinizing the motors. I didn't know that you could still get BBs from Crusader or Mercruiser, and are they 496s or 502s?

Good luck.

John

[John Nardi]

Actually, after continuing my research, the engine of choice is the 8.1 496 cu in 375 HP... Unreal, if you go 8.2, it is strictly 100% digital and adds a very significant amount to the install...Also, these 496's are around 15K without the gears...It is amazing how the price jumps when going from a 454/350 to the 496/375...A remanufactured 270 or 300 can still be purchased for 17-17.5K each...I would like the boat to do an honest loaded 30 knots when the sea conditions permit; so even though the price would be correct, the 454s won't do it, and one has to take a very hard look before spending those kind of dollars on a gas refit....What would be the apples to apples running/fuel burn stats on the 270s versus the 300s?? Thanks, John

[Carl]

I don't know anything about the Cummins 504s.

John

504's
Big, heavy and 195hp...


So provided beds are in good shape and not cranking up the hp it should/could be a swap to a smaller lighter diesel motor.

[STraenkle]

John, I actually have the 496 Mag MPI HO (425 HP) in my 31. Got a great deal on the engines as running take outs from a diesel conversion, 16k for both with ZF gears and 250 hours on the engines. Tight fit height wise. Had to push the motors as far back as possible and remove the sound barrier and cut a little off the Plastic cover on the engines. But they fit and don't hit anything.

I am way under propped and still running the 1 3/8 shafts. The gears were 2:1, the 1.5:1 would be much better, but price was right. The original wiring harness plugged right in, which surprised me. I also bought a tool for my laptop that plugs into the engine's computer and gives you all the information you could want, trouble codes, engine hours at different RPMs, throttle position, % throttle, fuel usage, sea water pressure, oil pressure, fuel pressure, engine temp, everything. So with my set up I can only run to 60% throttle before hitting the Rev Limiter at 5,000 RPM. However that pushes it along pretty well at 33 to 34 knots and watching the gas gauge fall. Do that every once in awhile for the last 3 mins of a trip. I cruise at 25 knots or 3,000 RPM and 33% throttle, which give a little over 1 nautical mile per gallon. About 10% better than the 454's and the engines are barely working to push it. I love fuel injected, press button and they just start, no choke, flooding, just push the button and leave the throttle alone. The engines will also go into a limp home mode if any thing goes wrong, low oil, low seawater pressure, over heat, etc. You can over ride this if needed or just a bad sensor.

[Priceless]

Obviously if money is no option go diesel. It's nice not to have to fill that tank every time you go out. With the 315 Yanmars we get 1.7 to 1.8 miles per gallon. Ran Priceless at 24-28 knots all last weekend. 7 hours cruising, 78 gallons fuel, almost as economical as the 23 Steiger with single two stroke 225 I Ran for 20 years---10-12 gph. The gas guys won't even go off shore because they run out of fuel. You should probably contact John Patnovic at Worton Creek Marina. He has been putting Cummins in his new refits since the YanMars aren't made anymore in that size. He can give you some good advice and realistic expectations.

[Tony Meola]

John

The 270's will get you a cruise of 23 to 25 knots st 2300 to2300 rpm's. I have the 270's and running light , no tower or hard top.

The 315's will get you a 28 knot cruise. Here is the issue, this is a 30 foot boat, how many days will you be able to cruise at 30 knots. The 270 will be plenty big enough if you stop and think about it. The fuel burn difference is small maybe 1 or 2 gallons hour with the 315 doing slightly better than the 270.

[John Nardi]

Thanks for all the great replies...The decision becomes a lot easier when the right deal at the right price crosses one's path...Thank God (careful what I wish for) I have at least six months of cosmetics to work on and look for the opportunities...Best, John