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-   -   Detroit Diesel 4-71 Engines (http://www.trawlerforum.com/forums/s6/detroit-diesel-4-71-engines-12987.html)

brian eiland 12-22-2013 09:09 PM

Detroit Diesel 4-71 Engines
 
A vessel has been brought to my attention that is equipped with twin 4-71 DD engines' It quoted as have 660 hp total,....330hp each.

Is that even possible with these size engines??

MC Escher 12-22-2013 09:17 PM

Theoretically, yeah... sure. HP is a function of engine speed and torque, which itself is determined by how much fuel you can burn (thus releasing energy) and how fast you could burn it.

BUT...

Since the X-71 series DD usually makes something in the area of 40hp/cylinder and 330hp is roughly twice that (~80hp/cylinder) I would be thinking that either:

a) Something got lost in translation,
b) Someone is lyin' his 4th point of contact off, or;
c) I don't want to be near that over-sized claymore when it's running.


EDIT: This is just an off-the-cuff opinion, which is subject to revision upon receipt of new information. I'm just saying that what I said is true, as far as I know.

brian eiland 12-22-2013 09:38 PM

1 Attachment(s)
I saw this on an engine forum
Quote:

DS, to give you an idea, I have seen 4-71's rated from 82 to 325 horsepower.
Usually they run in the 160-200 range, but marine applications with the DDEC chips are getting 300+ horsepower out of them.
...and another referenced an inclined or pancaked 4-71

and/or with turbo charging

kulas44 12-22-2013 10:33 PM

Covington and J&T did lots of things to the 71 and 92 series engines. A 4/71 at 330 hp sounds like one of those. Probably as good as the 8v71 at 650 hp. If ran hard expect very low hours before needing refreshed. If ran conservativly they can last a long time, but, at low loads they tend to "load up". They are definitely turbo'd/inner cooled and more than likely have blower bypasses. Not a good "slow" engine.

healhustler 12-22-2013 10:49 PM

[QUOTE=MC Escher;200612]
c) I don't want to be near that over-sized claymore when it's running.
/QUOTE]

I've had lots of 471's in lots of applications from 1946 GMC semi tractor to Oliver 99 farm tractor to mid-70's Ford straight trucks and had fun with all of them. When I think of the suffering that must be going on in a 71 series with 80+ HP per cylinder and the pressures that would require, I don't think that would be a fun engine unless the fun was to blow it up. Of course, I could be wrong about that.

kulas44 12-22-2013 11:29 PM

I recently read about an outfit that specializes in the old detroits converting a 4-53 to DDEC using the electronic injectors and a ECM from a 4-71. They said it ran great but the rpm limit was 2300, they wanted 3000 and had not figured how to do it yet. I dont know if the DDEC was an improvement or not but the article was interesting. I love the parts interchange on the old Detroits. And simplicity/durability.

FF 12-23-2013 06:39 AM

IF you want longevity 30-40 Hp per 71 cylinder is the norm.

At 1200RPM , prime gen set use, the engine life gets extreme!

Ron T 12-26-2013 02:31 PM

Dd-4-71
 
Just my view. Way to much HP to ask from that engine. Must have high RPM and high compression ratio to result in that HP. Short engine TBO.

kulas44 12-26-2013 04:19 PM

Lower compression actually, lots of turbo boost, big injectors. Rpm is usually 2750 max, not much more than standard.

Nomad Willy 12-26-2013 05:11 PM

Kulas44,
Brake mean effective pressure (BMEP) is what applies here. But you are absolutely right .... Lots of pressure and heat.

High rpm by itself shouldn't be a problem if the engine is designed to operate continuously at that speed. Excessive load and temps could easily be obtained w that engine IMO.

kulas44 12-26-2013 05:33 PM

And brake specific fuel consumption. Lower compression allows the input of more air from the turbo and allows the engine to utilize more fuel to make the requested power. Cylinder pressure needs to be controlled, to much and they go boom. The problem with this approach is that instead of 19 or 21 to 1 compression ratio the high output DDs are usually around 17 to 1. Thats ok on a new engine but with a little wear they get really hard to start because of it. You'll see lots of white smoke on startup and for longer periods of time, due to low cylinder temps, which is why it was hard to start. A lot of DDs were fitted with ether injection systems for this reason. Lower compression ratios are also one of the reasons these high output engines dont do so well at low speed and low loads. Being a 2 stroke they are basically aircooled at these loadings and cylinder temps are low, resulting in unburnt fuel.

FF 12-27-2013 06:23 AM

High rpm by itself shouldn't be a problem if the engine is designed to operate continuously at that speed.

Most of the 71 series I have seen MFG charts for show a 2100 RPM engine , except fire trucks .

>Rpm is usually 2750 max, not much more than standard.<

To me 2750 is a Loooong way from 2100.

RickB 12-27-2013 06:52 AM

The 4-71TI is rated at 325hp (310 prop curve) at 2600rpm. That engine is straight from DD, no aftermarket mods.

MC Escher 12-27-2013 04:13 PM

Quote:

Originally Posted by RickB (Post 201532)
The 4-71TI is rated at 325hp (310 prop curve) at 2600rpm. That engine is straight from DD, no aftermarket mods.


Well, I'll be...
Learn something new every day.

I'd be quite curious as to what sort of factory upgrades were done to the bottom end, because a doubling in power implies a doubling in cylinder pressure.

kulas44 12-27-2013 09:36 PM

No upgrades at all in the crank or rods. Pistons were trunk type two peice (IIRC). cam timing was different, for the injectors anyway. DDs have 3 settings on the cam, advanced, standard and retarded. All of which are dependent on the injector used and hp rating. Turbo engines had different ports in the liners. Any engine could be changed to any other config. easily. The DD was the most known diesel engine of all time. If you need 100 hp constantly in the most economically possible way a DD is the way to go. Not so good above or below this need, or any quoted hp requirement.

MC Escher 12-27-2013 11:46 PM

Interesting, and impressive.

FF 12-28-2013 06:58 AM

I'd be quite curious as to what sort of factory upgrades were done to the bottom end, because a doubling in power implies a doubling in cylinder pressure.

Running 80 Hp from an engine that normally does 30-40 hp per cylinder with a turbo and inter cooling simply reduces the engine service life.

Many of the Sport Fish fold think 1000hours to overhaul is a great engine!

RickB 12-28-2013 08:31 AM

Quote:

Originally Posted by FF (Post 201781)
I'd be quite curious as to what sort of factory upgrades were done to the bottom end, because a doubling in power implies a doubling in cylinder pressure.

That ignores the fact that the high power engine develops its rated output at a higher rpm and ignores the fact that the engine uses a bypass blower that at high power is essentially non-existent compared to the large parasitic load imposed by the standard blower.

Also, don't for one moment think that BMEP is actual cylinder pressure.

Consider that the larger number of power strokes resulting from the increased rpm above the NA version, along with the availability of the power that is consumed by the blower on the NA versions, along with higher volumetric efficiency and better scavenging contribute greatly to power output.

Frank Tew 09-09-2019 10:48 AM

Fuel Consumption
 
I ran across this thread and I do have a couple of 1985 471T, N90 injectors (rated at 325bhp) engines J & T converted. These engines run great, no smoking and very little oil consumption.
I was hoping someone would have some information on fuel consumption as my manual offers no tables.

Comodave 09-09-2019 11:17 AM

Welcome aboard. Maybe check boatdiesel.com.


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