Detroit Diesel 4-71 NA

[Captain DJ]

If I remember right, the blowers produce about 6psi at full rpm. Normally a turbo Detroit has a lower compression ratio. With turbos on a natural you'd get much higher temps and combustion would be much hotter, shortening the time between overhauls, maybe burning valves and injector tips. And with smaller injector, a much lower fuel/air ratio. Fuel is part of the cooling. Fuel is passing thru the injectors all the time, cooling the tips between firings. And even though the fuel is heated from passing thru the head, it's 1000° cooler than the piston tops. And with smaller injectors you get some lesser amount of cooling. My experience with smaller injectors is loss of higher rpm. The governor doesn't know what injector is installed, so it just opens the injector as far as it can until it's wide open. It still takes fuel to create hp.
The nice thing about naturals is long life, at least 3x longer than turbo models. It probably costs a lot more to rebuild the engine than buying more fuel.

I get better mileage out of my engines by adjusting each cylinder to have the same exhaust temp by how I adjust the rockers, and I use a fuel conditioner (archoil AR6200) that does the usual stuff, but also makes the fuel combust better and gives me 6-10% better fuel economy depending on how much conditioner I use. And I have self made hydrogen generators that break down water into 2 hydrogen, 1 oxygen molecules that is fed into the intake. The hydrogen is additional fuel and the oxygen improves the burn. That gives more than another 10% improvement. So while I should be burning 6 gallons/hour per engine at 1800, I burn a little less than 4.25 gallons/hour. If I did the math right, about 30% better mileage.

I would REALLY like to learn more about the hydrogen generator.
I had 4-53s with the smallest injectors and they were FINE engines. Now I have Ford Lehman 120s and miss my old DDs.
With a 40 gallon/40 inch high Day Tank(with sight gauges) I used 1.35 gallons per hour/engine or 2.7/hr for a GB42-125 woodie. (at 1450 rpms, flat water and 6.75 knots) using magnets on fuel lines and 2 micron pre-cleaned fuel, frequent oil changes and a Lucas Oil additive. They purred. I named them Jake and Bertha. Now these FL120s (unnamed as of yet) throw a sheen on startup and according to FloScan gauges use about 2.5 to 3.1 gallons/hr each (at 1800 rpm and 7 knts), and on a much smaller FG boat...I have only had her one season and am hoping the FloScan meters are just out of calibration or something. I always like the KISS approach of a verifiable Day Tank for pre-cleaned fuel to come from and return to, so I will know each day what was really used.
I have always enjoyed and appreciated your input and knowledge you share on this forum. Please keep it going pal.

Best regards,

DJ

 

[Captain DJ]

Makes sense @FF. However bear in mind that a 2 stroke’s big blower is moving a large volume of air through the case and cooling off the block. At low rpm’s the block does not get up to proper operating temperature.

So based on the thread above, and your and @Ski’s comments, it’s starting to sound like 1200 rpm might be that point where continuous operation below that point (with the associated low load from a prop at that rpm) would be not recommended. The engine and the oil would not be able to reach a healthy operating temp.

I believe, and I may be wrong, but my belief is it depends on water and ambient temperatures. I had 4-53's NA with smallest injectors, ran at 1400 RPMs and achieved awesome 1.35/gph/engine at almost 7 knots, in flat, warm water. If water temp is low 80s and air temp is in high 80s to 100 it has to make a difference compared to PNW temps like low 50s water and barely 70s air. My old DDs never needed "blowing out" but were used often, constantly on the move. And I had extremely clean 2 micron fresh fuel and rigorous oil changes.

Like to hear if water temps and air temps play any role on achieving operational temps...or maybe I am wrong.

 

[Bugaboo]

I would REALLY like to learn more about the hydrogen generator.
I had 4-53s with the smallest injectors and they were FINE engines. Now I have Ford Lehman 120s and miss my old DDs.
With a 40 gallon/40 inch high Day Tank(with sight gauges) I used 1.35 gallons per hour/engine or 2.7/hr for a GB42-125 woodie. (at 1450 rpms, flat water and 6.75 knots) using magnets on fuel lines and 2 micron pre-cleaned fuel, frequent oil changes and a Lucas Oil additive. They purred. I named them Jake and Bertha. Now these FL120s (unnamed as of yet) throw a sheen on startup and according to FloScan gauges use about 2.5 to 3.1 gallons/hr each (at 1800 rpm and 7 knts), and on a much smaller FG boat...I have only had her one season and am hoping the FloScan meters are just out of calibration or something. I always like the KISS approach of a verifiable Day Tank for pre-cleaned fuel to come from and return to, so I will know each day what was really used.
I have always enjoyed and appreciated your input and knowledge you share on this forum. Please keep it going pal.

Best regards,

DJ

Detroit ford

 

[Island Cessna]

That makes more sense

And the 6-71’s leftover from the war powered everything from boats to sawmills to goodness knows what for another decade or two!

 

[Nomad Willy]

This fishboat in Petersburg Ak had a 4-71.

 

[Cleanslate]

Hi Lepke.
Met you on a different site.
Always liked your DD knowledge.
I just joined TF this week.
I have twin JT DD 471 with M15 ( M95) injectors , yup, ! J &T hot rods .
But I don’t run them hard . 1600 RPMs mostly; 2000 RPMs at times.
Can you explain to me the difference in Microns for the primary fuel filters .
I’ve been told to run 30 Racor in my boat.
I see you use 2. Would that benefit me?
Or are my motors to thirsty for fuel ?
Would it. Cause problems.