CAT 3126 - economy / performance tuning

The way I understand it is, you want to match fuel delivery with RPM's, otherwise you're dumping too little or too much fuel per ignition. Dumping too much fuel into a cylinder will not ignite it all, wash the oil off the liner, etc... So prop tuning and making sure the fuel rack is all calibrated will probably yield good results. Just getting everything to factory spec will get you a 60% increase in economy from the numbers you threw out, no need for fancy doodads or super blowers or boostermabobs. Much better than the 5% you're looking for.


The biggest problem with too much fuel is high EGTs. Unburned fuel is the black smoke seen in the exhaust, and means the turbos are not supplying enough oxygen in the charge air to burn the fuel available based on the current ignition timing (amount, duration of fuel injected).

There is no rich or lean in diesels - just fuel, air, cylinder pressure, and timing of the injection event.

CAT has tuned for 2800rpm @ WOT on the 3126. Props are matched to hulls and anticipated loads, like selecting drive tires on a truck. The same hull could be propelled with a target RPM of 2600 or 3000. Longevity would be a factor - what becomes the weakest link?

Fun stuff. I bet there is more performance and efficiency in there...just waiting to get out. :smt001
 
Which is my point, clean the filters, pull and clean your aftercoolers, set your fuel rack, check your turbos, tune your props, pull your injectors and have them cleaned and tested. You've got a ton of low hanging fruit here. You "should" be pushing 1.2mpg. I'm getting 1.1 to 1.2 and my boat is bigger and heavier and I have the 420hp engines which suck more fuel.
 
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Which is my point, clean the filters, pull and clean your aftercoolers, set your fuel rack, check your turbos, tune your props, pull your injectors and have them cleaned and tested. You've got a ton of low hanging fruit here. You "should" be pushing 1.2mpg. I'm getting 1.1 to 1.2 and my boat is bigger and heavier and I have the 420hp engines which suck more fuel.

All of the above will be done. Q: How many hours do you have on, and what oil has been used? i.e. Did you ever use multi-viscosity oil before CAT changed their spec to straight weight, and did you experience aftercooler fouling as a result?

FYI: My mileage was not accurately calculated as it used 'estimated trip miles' based on our online trip planner, not actual miles traveled, which were likely more. We also had bad fuel at the beginning of the trip, and boat was not operated with fuel conservation in mind. It was probably better than reported - this spring I'll get good numbers from the get-go.
 
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Yes, the PO used multi-viscosity oil and I had to pull the aftercoolers and have them cleaned, they were all plugged up. I've switched to Rotella 30 weight.
 
To partially answer the oil question, I have 1400 hours on my engines and have used single viscosity Rotella T SAE-40 since Caterpillar changed the fluid recommendations. My engines had 15W40 miltiviscosity oil in them for 125 hours or 2 seasons. I do not have any build up in the aftercoolers and have never had to clean them.
 
To partially answer the oil question, I have 1400 hours on my engines and have used single viscosity Rotella T SAE-40 since Caterpillar changed the fluid recommendations. My engines had 15W40 miltiviscosity oil in them for 125 hours or 2 seasons. I do not have any build up in the aftercoolers and have never had to clean them.


Good to know that the right oil does make a difference.

The maintenance history I was provided does not specify what type of oils were used. From the partial jug of 15/40 Rotella onboard, my safe assumption a multi-viscosity oil has always been used. Once I change the oil out with straight weight, I'll pull the aftercoolers, inspect and clean them.
 
And you also mentioned you got that nasty drips from the turbo to aftercooler hose. That right there is a smoking gun that your aftercoolers are crudded up and your turbo is trying to push through it. Switch oil, clean the aftercoolers and I bet you see different numbers. Just cleaning my airfilters will give me another knot.
 
If you really want to get deep into diesels check out www.boatdiesel.com it is the by far the best website and forum out there for marine diesels.

Thanks for the nudge. I had actually signed on last summer while researching our potential purchase, found what I needed, but did not buy a membership.

Today I did buy a membership, and immediately found this article called 'Propellers Move Boats - Engines Only Turn Them' that completely explains (in laymens terms) the relationship of marine diesel engines, props, overpropping, and the effects of adding power.

http://boatdiesel.com/Articles/Articles.cfm?P=20120116_Introduction.cfm
 
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And you also mentioned you got that nasty drips from the turbo to aftercooler hose. That right there is a smoking gun that your aftercoolers are crudded up and your turbo is trying to push through it. Switch oil, clean the aftercoolers and I bet you see different numbers. Just cleaning my airfilters will give me another knot.


Agreed. I'll do this one myself, after getting the right oil in early this season.
 
Looked into a few performance specs this morning before my day started. The high performance marine 3208 toped out at 450 hp @ 2800 rpm with bare engine high idle at 3130 (pushing valve float limits!). A very few with ratings of 475 hp. were also produced. I’ve personally been on a pair of factory +500’s that maintained 2600 rpm from Chicago to the Straights of Mackinaw with no harm done. Unfortunately the 3208 pistons were not round but oval! The needed to warm up to become round and then fit the bore. Push them too hard, too long and they would scuff and seize due to two ring design not transferring heat and unstable coolant temps in the V-8 design. However the lower end with its splayed main bearing caps was capable of more than the pistons could be cooled. Still one tough little old school motor. Sweet spot for best fuel/power ratio 1800 - 2000 rpm’s

The 3100’s were a far superior design. Corrugated block with stable cooling. +28,000 psi injection pressures with no timing advance needed. Highest HP rating I’ve seen toped out at 485 advertised @ 2960 with bare engine high idle of 3355 (valve float just over 3400 rpms). Sweet spot fuel/HP ratio 1900 - 2000 rpm’s.

Now keep in mind those +500 hp 3208’s were factory race motors that were basically a 435 with the fuel screws taken out and a turbo fitted on them the size of a small suit case…. The 485 3126’s are Military spec Navy seal motors that actually dynoed at 500hp. (Cats small engine dyno only goes to 500 hp!).

So propping for a cruise speed of 2000 rpm’s, working the mid range torque and top end HP some (within pleasure craft reason) may not cost you more than a tune up with injectors and turbo’s…. Injectors and turbo’s don’t last fore ever and it’s best to change them before failure.
 
Other than doing a play test on the turbo shaft, how else can you measure turbo life? Also on injector life, would you measure it in engine hours or fuel burned? I'm also guessing you need to take into account if it's low sulfur fuel or if lubricity has been added to it.
 
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Hello - back with an update. Ran the boat about 65miles from Superior, WI to Bayfield WI. Perfect mirror flat calm conditions most of the way in the late afternoon.

New impellors. Aftercoolers cleaned. Fresh Delo 30W. New fuel filters at the engine. No waste or fresh water, no gear, no food in the fridge, coolers, ice, wife, nothing. Just me and a near bare boat.

With engine sync OFF - I can manually balance both engines at 2800 and make 34.6mph. At manual WOT starboard makes 2850 and port makes 2775, unbalanced.

With engine sync ON - 2800 at 34.7mph best. Starboard tends to run a tad slow...maybe 2750.


Port water temp 175. Starboard 185. Probably gauge or sender error. Oil pressure 50psi both sides.


Do these numbers sound about right?
 
You failed to mention the bottom condition. Based on the title of this thread and assuming that it is a fresh bottom and has no growth or slime anywhere and the props are painted, then your numbers are good, except that you more than likely need to have the props tweaked to even the load between sides. However, 75 rpm differential isn't enough to break a sweat over.......I would wait until the next haul out and make that call after you load the boat with normal gear and passengers and run it a while.
 
I don't like the port reading low on rpms. I feel you should confirm engine high idle on both engines with a photo tach. Confirm governor control lever breakover And also confirm throttle cable adjustment. Then perhaps you can confirm the accuracy of your tachs.
 
I agree with Ron. If you are barely making rated WOT RPM with a VERY light boat, then, as you add fuel, water, stuff AND as the season goes on and your bottom dirties up a bit, you are sure to be well below rated WOT RPM and will be overloading the engines.
 
I don't like the port reading low on rpms. I feel you should confirm engine high idle on both engines with a photo tach. Confirm governor control lever breakover And also confirm throttle cable adjustment. Then perhaps you can confirm the accuracy of your tachs.

All good suggestions, and places to start. Starboard throttle linkage was removed for impellor / aftercooler repairs so that is where I will start to ensure it was replaced correctly and everything tight.

Nothing is that far from spec at this point. They just need some tuning and attention to detail.
 
I agree with Ron. If you are barely making rated WOT RPM with a VERY light boat, then, as you add fuel, water, stuff AND as the season goes on and your bottom dirties up a bit, you are sure to be well below rated WOT RPM and will be overloading the engines.

There is little to no 'dirtying up' on Lake Superior. At the end of the season, it looks about like the beginning. Maybe 1/8" of slippery slime to powerwash off the bottom paint.
 

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