SportFishing and Charters Forum - Detroit 6-71s WOT question

1989 turbo diesel 6-71's -- in a 48 Ocean sportie. Had my main set of props eaten up by stray current or something - and now on spare set. I am not sure these props are pitched right.

What should these engines turn WOT? I want to say 2400 - but prop guy said he thought maybe a touch higher, say 2500. Could make a difference in assessing the props....

thanks in advance...

I think you will need more info to determine the wot rpm. The higher hp detroits generally turn more rpm. model and serial on the side of the block below the head should be whats needed.

I think you will need more info to determine the wot rpm. The higher hp detroits generally turn more rpm. model and serial on the side of the block below the head should be whats needed.

You may be right. I do know that this very engine package was installed on a ton of 86-89 model 48s - and hoping to run into another owner/operator of one on THT.

24-2500 is screaming with those engines. we have them as generators on the tug I work on, we turn 1800 continous.

My cheif enginner says 2100 for no load applications max, 2000 full load continous duty.

671 TI's should turn 2650-2700 in neutral and are rated for 2500 WOT. WOT being wide open throttle in gear. In reality you want them to turn 2550-2600 fully loaded with a clean bottom. That way they'll still turn 2500 later in the season.

That's not screaming for these engines. Not at all. However 2400 WOT will burn them up quick. The engines will not be able to cool properly if they can't turn WOT + rpm.

24-2500 is screaming with those engines. we have them as generators on the tug I work on, we turn 1800 continous.

My cheif enginner says 2100 for no load applications max, 2000 full load continous duty.

They, like all smaller diesel engines, turn 1,800 rpms (real small ones will turn 3,600 rpm) on generators, because that is how you get 60 cycle AC current without using a gearbox.

The above poster is 100% right - 2,500 rpm @ wot minimum - propped to 2,600 rpm (if 450 or 485 hp TIB's) or 2,550 (if 435 hp TI's) and cruised at 2,200 rpm.

However 2400 WOT will burn them up quick. The engines will not be able to cool properly if they can't turn WOT + rpm.

Not sure I understand what you mean by that - would appreciate a clarification.

FYI In our engine survey 16 months ago, they turned almost 3000 on the "no load" rev test - meaning in neutral. We all cringed but that's what the engine surveyor did.

Model and serial, then we can find out what they are and their specs.

Not sure I understand what you mean by that - would appreciate a clarification.

FYI In our engine survey 16 months ago, they turned almost 3000 on the "no load" rev test - meaning in neutral. We all cringed but that's what the engine surveyor did.


WOT = Wide Open throttle. Literally pushed all the way open. Detroit, J&T, Covington, etc rate the engines to turn a certain rpm at WOT (2500 in this case). If the engines cannot turn the rated rpm they are overloaded. If they can just barely get to the rated rpm then any changes to the boat will cause them to be overloaded. An overloaded engine may show ok on the temperature gauge but have internal hot spots that cause rapid failure. A 671 TI that can turn 2550-2600 rpm in gear will probably last 3-4 times as long as one that can only turn 2400 rpm in gear. That's why you hear about engines needing a rebuild in 700-1200 hours while someone else claims 3000-4000 hours.

You must use a digital tachometer or the readings. Analog tachs are useless for testing. 3000 rpm won't hurt these engines. I know mechanics who have had run-a-ways that didn't blow at 4500 rpm. The governor should be adjusted however.

2500 under load...

My DDEC II's turn 2350+ WOT, if that Helps.

The engines will not be able to cool properly if they can't turn WOT + rpm.

Oh dear Lord PUHLEEZE - I know what WOT means. What I don't know is what you meant by not being able to cool properly if they can't turn WOT plus rpm -- and yes, I know what RPM stands for but I don't understand the way you constructed that situation.

Detroit and J&T heat exchangers were marginal. If the boat is overpropped it will not run at the customary max cruise WOT-400rpm without overheating.

If you have the 6-71 TI or TIB's, running overpropped is absolutely guaranteed to cost you big, and quickly.

If you have a J&T, check for a sticker on the valve cover with loaded and no load RPM on it.

Detroit and J&T heat exchangers were marginal. If the boat is overpropped it will not run at the customary max cruise WOT-400rpm without overheating.

If you have the 6-71 TI or TIB's, running overpropped is absolutely guaranteed to cost you big, and quickly.

If you have a J&T, check for a sticker on the valve cover with loaded and no load RPM on it.

Would that be over heating as registered on the bridge or would that be over heating on the unmonitored areas?

Would this effect WOT - 600 or so also?