Gray Marine 6-71 Fuel Burn

[mr_showboater]

Anyone know what approx the fuel burn would be for Detroit Diesel 6-71 engine in a 10,000 lbs landing craft? Just wondering if I could afford to take one out of the harbor, haha

I have read on the forum perhaps 1 Gal per cylinder per hour? Is it really that high, or is that wide open? Wikipedia said that this LCVP could do 12 knots (14 mph; 22 km/h) (light?) I think.

Would it be a smart move to pull it and put a Cummings BT4 crate engine in it instead, or maybe something else? I am interested in running barley above idle, don't care if A to B takes a few more hours also want to keep it simple. Advice needed for a newbie and Thanks.

 

[tiltrider1]

Its all about HP. A 6-71 burns about 1 gallon of diesel per hour for 18 HP. So, if you need 180 HP for one hour you will burn 10 gallons.

How fast you travel will determine how much HP you need.

 

[O C Diver]

Its all about HP. A 6-71 burns about 1 gallon of diesel per hour for 18 HP. So, if you need 180 HP for one hour you will burn 10 gallons.

How fast you travel will determine how much HP you need.

That consumption to HP number would be optimistic from what I've been told. 16 HP per gallon was the ratio I've heard most.

Regarding actual Gray Marine engines:
I had one in a charter boat. The engine was built in 1944. Some time in the 60's or 70s the Navy commissioned a practice torpedo recovery boat from a builder in Maine. The Navy sent the builder the 6-71 Gray Marine along with a mechanical (not hydraulic) Twin Disc transmission. The Navy used the boat for less than 10 years, as the torpedoes got longer and a new boat was required. Thus was the origin of my steel hulled charter boat.

Anyway, WW2 Gray Marine 6-71s were 168 HP and could burn about 10 gallons an hour on the pin. At least mine was 168 HP but never run on the pin.

Ted

 

[magna 6882]

I remember as a teenager running 671s in trucks and being a 2 stroke that was supercharged they didnt do all that good running at low rpms for long. The airboxes would fill up with oil and smoke like hell when rpms came up. These were trucks. We were told by the shop to run them flat out rather then grab another gear.

 

[Crux]

Since its Gray Marine, it may well have 2 valve per cyl head and 'C' injectors....runs fine but will have a bit of black smoke.

Beginning in about '70 they had 4 valve heads, 'N' injectors, and taller cylinder
ports and pistons.....so higher compression and and much cleaner exhaust....naturally aspirated at 238hp.

The older 'C' eng can be rebuilt to 'N' style, so see which you have.

 

[Mako]

My 1940's Grays generated about 16.3 hp/gal-hr. The newer 4 valve head models about 18.3 hp/gal-hr, which is a typical number for most all the mechanical engines of that era (Cats, Cummins, Fords, etc.).

I you want to afford the fuel then travel slower.