46 Post performance

Hi RT46

Mine are 671 TI's - 410 Hp ea.
I believe yours might be 485 hp ea.

No load 2650
Full load 2550
I cruise at 2000 to 2250 rpm.
wheels are 24X24
My burn rate is 25 Gallons per hour which includes the genny
About 20 knots at 2000 and about 22 knots at 2250.
I run the genny every time I leave the slip for exercise if nothing else.
I also always run it with a load.

Can I ask what it cost you to have that work done and did you farm it out or do it yourself ?

Do you have cast iron heat exchanger ?

That is a kind of personal question so I understand if you don't wanna share the $ part.

I have about 3500 hrs on my 671's
They run great.
They white/gray smoke like heck when they are cold but stop once at temp.
They run about 170* according to gauges and confirmed with mini temp.
Never any soot on the transom.
I replaced the cast iron heat exchangers a few years ago and it made a world of difference.

Anyway, good luck with the rebuild and the boat.
I love my 46 and more importantly, my wife really loves it.

Regards

It sounds like you're not making nearly the HP the engines should be making, either that or the boat is very heavy compared to when it was built, or the bottom is very dirty. You're Max RPM at full throttle should be much higher then what it is.

I'm not an expert on 6-71 but many diesel will suffer premature failures when they do not produce full load RPM. I recommend you get this checked out /corrected ASAP.

Correct. 485hp 671 TIB's will die a very quick death if they are only able to turn 2150 rpm WOT. Sounds like you are very overloaded. They are probably one of the worst engines for durability when overloaded like that. Neither the OP nor Chesapeake46 posted their transmission ratios. However if we assume they are the same then the OP may have a bottom fouling problem, propeller problem or a great deal more weight. Any of which is causing severe overloading. If the ratios are different then their may be other issues preventing the engine from reaching the proper rpm while loaded.

However I would not run the boat on plane for anything more than testing until the problem is corrected. The engine can not cool its internal components correctly when overloaded. Coolant temperature could be ok while the piston crowns are cooking. You want to be able to hit about 2550 rpm with full tanks/load and a freshly cleaned bottom. 2650-2700 rpm no load is good. You will need to verify all these numbers with a digital tachometer.

Post 46

How much did the rebuild cost per engine?

Thanks

I had occasional high temperatures when the raw water temp in the bay was high, the humidity was high and the cast exchangers and raw water system were dirty.

It was a maintenance thing for me to clean the exchangers each year, a couple times a year, with hydrochloric acid.

My Detroit mechanic friend suggested replacing the cast units with lenco units (http://www.lencocoolers.com/ ).

I had a long talk with a J&T technition.
He said the cast iron exchangers were plenty big enough for my 410's and that I should have them ultra-sonically cleaned and my problem would disappear.
He said that J&T had some redicules high amount of hours on the cast exchangers and they are plenty, plenty big enough.
He said the LENCO type exchagers would only last about 5 years and then you throw them away.

I also have a Post friend that did ultra-sonically clean his exchangers and he was very happy with the results but he had just had it done with no real time on the engines at that time.

That being said, my Detroit mechanic freind added that J&T's testing was in a shop environment.
No algea, no crude in the water, etc.

When my brass cooling tubes for the raw water began to fail, I just decided to replace the brass with stainless steel and try the Lenco's.

No more Hydrochloric acid ( which is another story ) and the engine temps never climb over 180 even in the most humid air and hot water temperatures
Since.
This was about 6 years ago and roughly 100 to 125 hrs a year.

Long winded but I tried to include all variables.

EGT's at 1950rpms with that much load considering WOT 2150rpms, tell me you're getting too much fuel and not enough air. 200rpm's shy of WOT and overloaded, you should be seeing 800+ I would think even closer to 900 (which is way too high) with that overloaded situation. I would expect black smoke at cruise as well. Either the rack is set up wrong, you're not making the compression you should be, or the turbo's aren't supplying enough air. I would put boost gauges on the engines, fuel pressure, etc. Also check to make sure you're getting full throttle travel (at the dock) and you don't need to adjust your throttle cables as well.

Sounds to me like you're missing some power and airflow somewhere. Take the air filter elements off and run it without them and see if that changes anything, could be restricted air filters. I've seen the K+N style air filters crush at high rpm's and close up after being washed one too many times.

I know you are looking for 46 performance, but I can tell you for my 43: I have 450 horsepower, you have 485. Same transmissions. Your boat is heavier\longer and holds 150 more gallons of fuel. I am running 24x25 3 blade with a cup and getting 2500+ max rpm. I think the prop shop saying 24x24 with some cup is where you should be.

Those numbers look much much better. EGT's seem pretty good. On those engines 900 degrees is about the high end you want to be at. Are those WOT numbers full fuel, water, etc and verified with a digital? Ideally you would want to see about 2550 but you are very close. Your engines should last many times longer with those new props on.

The EGT numbers are related to load so the cruise at 1950 rpm / 17 knots seems to be pretty efficient on paper. Even if you go up to the higher RPM to get more speed you won't burn any more fuel than you did before but your engines won't be working as hard. Plus it looks like you picked up 2 knots of "emergency" speed.

Side note to those who put down our noisy Detroits - I just replaced the fuel pump on my 671TI - cost $93. Price shop that against a new common rail fuel pump....

Your numbers look a heck of a lot better. I ran a 38' Buddy Davis SF with the same engines and they seemed to cruise the boat best and seemed to run the easiest right around 2100 rpms, but obviously it's a different hull. Personally I would cruise them at an rpm where EGT is between 750-800 degrees, no more than 800, if not closer to 750......

Sounds like you have this under control.

One thing to inspect. The 6-71s on my Viking have external senders for the oil pressure guages and alarms. Check these and replace if necessary. I can tell you from experience that if one lets go, you will drop the whole load of oil in the bilge in a matter of minutes. Not a mess I want to deal with again.

Good luck.

Hi chesapeake46, just curious, how are the Lenco heat exchangers doing?
I'm looking for renewing mine, no hurry, but they get old and thin so...
If you have a picture, that would be great!!
Thnx!!

Hi P46,
The Lencos are great for my use. I think you probably put more hours on your boat than mine which may shorten their life span.
I had a stainless steel cradle fabricated from a pattern I made which worked out pretty well.
I had to move the floor supports forward some to allow me to pass between them and the Lenco's because they are a little deeper than the old cast iron ones.
I am a little thicker than I used to be too.
I'll will be there tomorrow, Ill take a picture.

LOL... same here, could lose some weight too!

Look forward to you pictures, you have them over 5 years already and I make only 150 hours a year on the engines, but spend thousands of hours a year on the boat... we are limited on an Island and fun is concentrated 'around the corner'... ;-))