CAT 3126 - economy / performance tuning

markrinker

markrinker

New Member
Jul 19, 2011
325
Lake Union - Seattle, WA
Boat Info
2000 410DA
Engines
Caterpillar 3126
Okay I know this is stepping into territory bound to raise spirited responses...before I even ask, I'll preface my questions with the following statement of knowledge:

"I have over 800K diesel powered highway towing miles to my credit, and understand the complex and delicate nature of additional fueling, boost, load, RPMs, etc. In those miles I have added additional fuel rates, adjusted mechanical wastegates and boost feedback loops, fumigated with propane. In those experiences, I have made gobs of additional power, saved thousands of dollars on otherwise wasted fuel, and learned the hard way about blown head gaskets, transmission slippage, and prematurely worn out more than a few sets of expensive Michelin tires that cost more than the fuel saved... therefore, I am done with diesel hotrodding, but am not afraid of fine tuning for best application performance."



Question: Anyone done any tuning to boost levels and/or additional fuel rates on a 3126? How about prop changes, in search of better fuel economy, quicker on plane performance, or higher cruise speeds?

Just got back from the Seattle Boat Show and had a great conversation with the prop folks at www.ACMEMarine.com - I know they are in the business of selling props - but it did get me thinking about what could be done to safely performance tune my CATs this season, with the following goals of:
  • Generating a set of spare props (my OEM factory takeoffs would become the ready spares)
  • Better fuel economy (pays for new props over time)
  • Lower or same EGTs
  • Better on plane/cruise performance
My experience has been that most factory engineered fuel/boost tunes purposefully leave some of the above on the table, in exchange for engine longevity and/or acceptable performance in all possible operating conditions (i.e. engines will hang together at WOT and a full load of fuel, water, passengers and gear in any conceivable Florida or Arizona ambient air/water temps, to the detriment of peak performance and economies possible at average Lake Superior air/water temps, with more realistic loads of fuel, water, passengers and gear.)

I also have a very conservative hand on the throttle, and a watchful eye on the gauges. Having acceleration power in reserve that is never tapped for long range cruises is well within my knowledge and responsibility...

What say ye? Leave 'em alone!!! or dig in and save enough on fuel in the next two seasons to pay for a new set of wheels? If the latter - who are the go-to people for experienced tuning experience?
 
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Probably an obvious statement, but the most important thing with marine diesels is to make sure they turn up the recommended WOT under full load and fuel. Overpropping an engine will give you a faster cruise and top end but will quickly wreck an engine.

Changing from 3 to 4, or from 3 to 4 blade props will give you different benefits, but changing the fuel mixture, boost, etc., generally is not recommended on marine engines. Changing one spec on the engine often requires you to make adjustments elsewhere, like props, shafts, air flow, filters....

JK
 
Agreed. Lots of times in racing, builders will actually start with the best tires available for the application, and work everything backwards from there.

Maybe my right question is then: Are the factory props on a 2000 410DA optimal for that hull and weight? If not, what prop could be substituted (without swapping shafts and leaving the transmissions stock) and what changes would then need to be made to fuel/boost settings on the CAT 3126 engines to match the new props?

Again, at least a 3-5% overall economy gain, with quicker on plane performance to cruise speeds would be the only reason to spend $3500 on a new set of props, IMO. No amount of additional top end performance would be worth the expense. You'd be spending money to spend more money.

If nobody has ever done it, then its likely that it can't be done - i.e. the factory props and factory 3126 settings are close enough to optimal to simply leave them be, and find a spare set of cheaper used props to bring along as spares.
 
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I have no comment on tweaking the 3126.......other than I wouldn't do it.

Now, I did just put on a new set of ACME's this past season and am extremely impressed with them. My boat had prop issues from the time that I bought it so I cannot say what the performance difference would have been between the ACME's and a descent pair of Hy-torq's. I will say that they made all the difference in the world for my boat and I attribute that to the design and to them being machined from a solid chunk of Nibral vs formed. You can see every pass that the ball endmill made during the machining process and I believe this adds "grip" to the surface. Sounds silly, but whatever the reason, it works. You will pay more for a set of ACME's but I belive it was well worth the upgrade.
 
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I would argue you have to look at the application. I'm more interested in the motors running for 100 hours straight to get me up the coast than racing the shrimp boat at the stop light.... Can't really pull over when I'm out 20 miles in the north atlantic.....

Then again... with CATs... crap is going to get ingested in the engine regardless of what you do to them. RACE AWAY!!!!
 
Another thing is that your props may be way different than what your boat left the factory with (ie..what Sea Ray thought was most efficient and probably was for a light load). Years of dings and dents and previous owners tweaking may have gotten them far from where they should be. You may want to start back at what was on it from the factory and then tweak them based off of your WOT.
 
quality time said:
Another thing is that your props may be way different than what your boat left the factory with (ie..what Sea Ray thought was most efficient and probably was for a light load). Years of dings and dents and previous owners tweaking may have gotten them far from where they should be. You may want to start back at what was on it from the factory and then tweak them based off of your WOT.
Click to expand...

Infraction.
 
Interesting post, and something I consider with every modification I make. I would be hesitant to make any changes to the factory fuel curve or boost calibration, considering the tremendous engineering resources they have at their disposal. To put it another way, if there was any "low hanging fruit", don't you think they would have pursued it already? Granted, there are are great many compromises made in the design and implementation of something as complex and intricate as a modern marine diesel, but efficient and complete combustion is always at the top of the "list".

You asked if there is a way to match the performance of the engines to the props, but I think a more proper question would be "how do I match the props, hull design, weight of the boat, etc. to the engines?" With that being said, I would consider the following, in your quest for improved performance:

1 - what can you do to reduce both form drag and appendage drag? A smooth bottom would be first on the list, followed by meticulous rudder alignment, profiled rudders and struts, and proper weight balance.

2 - Instead of considering re-tuning the engines, what about reduced back pressure? How many 90 degree bends could be removed from your exhaust? Would a custom exhaust reduce back pressure? Do you see sharp bends, changes in diameter, poor design, etc.? Anything you do on the exhaust side of the engine has the dual benefit of increased performance and efficiency. That's not the case when you add fuel or boost to gain performance.

3 - Once you have optimized the design in the previously mentioned ways, what is the optimum prop design for your intended use? I am a big fan of ACME props, as anyone who has read my blog knows. I use them myself. But you have to be very clear with them what exactly your goals are, and how you intend to use the boat.

4 - Take some weight out of the boat. Don't day trip with the dingy on the platform, 100 gallons of water you won't use, and a 300 pound relative you don't like in the cockpit. All these items should be left ashore unless you need them.

If you can leave behind TWO 300 pound relatives you don't like, even better.

Dale
 
quality time said:
I have no comment on tweaking the 3126.......other than I wouldn't do it.

Now, I did just put on a new set of ACME's this past season and am extremely impressed with them. My boat had prop issues from the time that I bought it so I cannot say what the performance difference would have been between the ACME's and a descent pair of Hy-torq's. I will say that they made all the difference in the world for my boat and I attribute that to the design and to them being machined from a solid chunk of Nibral vs formed. You can see every pass that the ball endmill made during the machining process and I believe this adds "grip" to the surface. Sounds silly, but whatever the reason, it works. You will pay more for a set of ACME's but I belive it was well worth the upgrade.
Click to expand...

Great to hear. I was impressed with what I saw of the ACMEs machining as well. What specifically were the problems you had with the factory set? I get very serious cavitation shudder under full WOT acceleration.
 
My issues were from the previous owner. I found out after the fact that they had sheared a shaft and lost one prop. He found a replacement that was "pretty close" but not nearly good enough swinging at 2400.
 
quality time said:
My issues were from the previous owner. I found out after the fact that they had sheared a shaft and lost one prop. He found a replacement that was "pretty close" but not nearly good enough swinging at 2400.
Click to expand...

You bought w!ngless' boat?!!!
 
The first step is to see what rpms you're turning at WOT. The next is to make sure your air filters are clean and in good shape, bottom is spotless and the paint is in great shape. Then pull the props and see what they are spec'd at, tune and try again. depending on the hours, you may need a valve and fuel rack adjustment... maybe the injectors cleaned and tested. Play with your tabs to find the right attitude the boat performs at. Spending $3500 on props when you have (assuming) perfectly fine props would be the last thing on my "need to buy" list. I would spend the money making sure everything is performing the way it was designed to. I would also pony up the $75 for new zincs to make sure the engines stick around down the road.
 
Sea Ray employs naval architects and propulsion engineers to determine the bst prop for the boats long before we ever get them. You may get a tad more out of more expensive props than standard, but its it worth the additional ownership cost? No.......but that is subjective. Here is another subjective point: if all you want to achieve is another 5% in efficiency, then pull the throttles back 50 rpm and enjoy the ride; if you want 5% more speed, then remove 5% of the weight in terms of gear/water/fuel/people, etc onboard.
 
All great points, and things I will factor into next years cruising plan. I am not in a hurry to spend money needlessly on promises, but am curious about what is possible.

GM employs legions of powertrain engineers. Ones smart enough to engage ISUZU and Allison to build a great drivetrain for the trucks they build and market. From 2001 to present, there have been multiple versions of the 6.6L Duramax. Each has built on, and improved on weaknesses that could only be exposed by hundreds of millions of user miles, gleaning warranty experience data, and direct customer feedback.

The aftermarket has consistantly come to market with products that served as stepping stones to the next verision of the Duramax.
  • In the LB7 series, a fuel map change, ignition timing + more boost would consistantly gain 10-15% fuel economy, while adding 60-70hp over stock. The initial product offering had been very conservative about pushing the capabilities of a new drivetrain.
  • In the LLY series, three+ years later, the factory added most of that HP, but changed turbos and had cooling problems with some trucks. (Some claimed insufficient oil cooling capacity, heat added by the new variable vane turbos)
  • In the LBZ series, the factory improved the intake (the aftermarket had been doing this for some time) and also made changes to fluid cooling, but the margin for aftermarket tuners was still narrow before fluid heat soak issues once again set in;
  • In the LMM series, the frontal area of the truck was drastically re-engineered, larger cooling stack, more thought to fluids cooling, once again even more HP potential found. To date cooling issues in even the most demanding situations are nearly non-existant, even when adding another 60-80hp over factory, into the 450hp range.
After owning all versions, and modifying the first three, My EPA-laden 2009 is the best truck yet in factory stock trim - the best power, the best mileage, the best overall towing capabilities. It took alot of time, patience, and careful incremental change to produce this truck.

I recognize the expertise and value of the SeaRay and CAT engineers, but believe they may be somewhat hamstrung by comparison once their (relatively low production numbers) products hit the water, and may not have the ability to make the incremental improvements (i.e. fine tuning) - mostly due to a very limited customer/warranty feedback loop by comparison to the Duramax example above.

My gut says there is potential for improvement. I may be entirely wrong, as marine power systems are always a very different animal. The ideas of "tuning the boat to its power" makes great sense. Also looking at any improvements on the exhaust side. Will do!

I think getting some good baseline stats early next summer will be my starting point. No hurry to throw parts or products at this project.


Thanks again, for all your ideas and input!
 
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Four Suns said:
Oh man... I can't believe Jim has banned the word *** from this site...
Click to expand...

That's just on the other site I belong to isn't it? I'm pretty sure I have a *** engine in my boat and that *** is allowed here.
 
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