40 pony upgrade- worth it?

T

tobnpr

New Member
Nov 12, 2006
3,246
New Port Richey, Florida
Boat Info
1988 300 DA
Engines
tw 350's w/ Alphas
It's "relatively" (and I use the word loosely) simple and inexpensive (in terms of diesel dollars)to hop up my 355's to 375 hp. Before I even bother to talk to my mechanics for an estimate (mostly injector pump changes) I wanted to get opinions as to whether it's worthwhile- at any cost.

40 ponies on a 20K+ pound boat- I doubt I'd see any noticeable increase in cruise speed. If I could get a solid knot more I might consider it.

Thoughts?
 
Mike,

Look at the torque/hp curves on the Cat.com site (I believe they are listed under marine engines; legacy engines). Then check the output at your normal cruising speed. You will probably find that the net gain at your cruise rpm's is less than the 40 hp, which would be at rated 2800 rpm.

I went thru this calculation some time ago for a friend on 375 hp 3208's. He was considering stepping the engines up to 435 hp when he was doing some injector repairs on one engine. Based on the charts, the net hp gain at 2400 rpm was only 38 hp vs. the gross gain of 60 hp @ 2800.

That doesn't answer your question, though.......i.e. how much speed will you gain? In the case above, the owner decided against the loss in fuel economy and spending the money to step up the engines so we never learned anything about speed.......this was in an older G&S custom sportfisherman so the speed wouldn't have been comparable anyway.
 
40 horse on a diesel usually means around 80 foot pounds, where 40 horse on a gas usually means around 40 foot pounds, so you would likely see more from it than from a similar gas upgrade. 40 horse is prob. more than a 10% gain, which could result in a little less than 10% increase in cruise speed, so that could bring you from 24 cruise to 26. Just some thoughts.
 
The 40 is both engines, current total is 710; so it's only a 5.6% inc. at WOT. As Frank said it's going to be less than 40 at 2400, but I'm not outputting 710 at 2400 either, so it's all relative to the power band as he said...

I'm thinking, if it ain't broke...
 
Are you willing to stress them to the limit? I've always been told higher HP from the same diesel = less life from the engine.

Just a thought.
 
dpmulvey said:
Are you willing to stress them to the limit? I've always been told higher HP from the same diesel = less life from the engine.

Just a thought.
Click to expand...

Generally true. But that's not even close to the "limit" for 3208's. They were available up to 450 hp in the "E" (pleasure) rating. 375 is the most common output; the 355's were only produced one year far as I know...
 
40 pony upgrade- worth it?

Just my opinion.....and it was probably more from a marketing prospective I'm sure, but at some point in the production cycle, CAT thought it was worth it!

This is a very similar situation with the 350 to 385 HP jump in the 3126-TA model. No added iron necessary.....simply turn a few screws, albiet very detailed and calibrated screws. To jump to the higher HP versions, you needed to change iron: Turbos, injectors, governors, etc...

Regardless, I don't think you would realize any HP advantage or increase in cruising speed (at the same RPMs) unless you also re-do your props.


Whick leads me to my 'very drawn out' question below....and it's not a question of is it worth it, or should I do it, or will it hurt the longevitiy of the motor...no....it's just a motor question (FW...that's your cue to enter stage right):

'Very specific' to the 3208 or the 3126 or ANY other motor where a HP bump requires NO additional iron.....ONLY fuel delivery or timing adjustments...or a chip change on the newer electronic motors......the same adjustments that CAT or Cummins or any other manufacturer does at their factory before the motor leaves the shipping dock....what would be the difference between 'making those HP adjustmens' and 'overpropping the motors'??????:huh:

Let's say you have two factory motors....XXXX-TAs. One leaves the factory rated at 350HP and the other leaves the factory at 390HP. Both are propped to make the rated 2800 WOT RPMs in identical boats. ALL the iron and fiberglass are identical....except for the fuel/timing calibrations and the props of course. The 390HP equipped boat would go faster, use more fuel and theoretically not last as long as the 350HP equipped boat.

Now let's say that you own the 350HP equipped boat and you want to cruise the same speed as your buddy in the 390HP boat....The way I see it, you basically have three options (assuming your buddy maintains cruising at the rated 2400 RPMs)....1.) give it more throttle 2.) have a trained tech come to the boat and make the necessary calibration changes to the motor and then re-pitch the props to match your buddy's or 3.) [and this is the cusp of my question] you could JUST re-pitch your props so that you cruise the same speed as your buddy at the same rated cruising RPMs as your buddy from the same motor (iron)....the only difference is...now you won't be able to make the rated WOT RPMs....you would be overpropped.

What's the difference between propping for the extra HP and re-calibrating the fuel/timing delivery for the extra HP? Wouldn't both motors be doing the same work at the same RPMs...just doing it differently? I'm sure the answer is simple, and I have my own thoughts, but I'm really kind of stuck on this one-......
 
I get the overpropping idea theoretically, but it then drops your max speed because you will not get the same 355 hp out of each engine since it is not able to turn its full designed and rated rpm's. also slower to plane, ect.
 
Eric:

I'm there with your response, but I'm talking more specificially where the HP bump isn't that great...like in the 355 to 375 or the 350 to 385....I don't think that there is going to be any real noticable time to plane differences in such a slight prop adjustment.....or....IS it just a slight prop adjusment to get a small HP bump at rated cruise RPMs?
 
The overpropping principle is not wrong for me also...it means you are going to have the best prop at the cruising rpm. That' s what I always thought! Why setting the prop for the maximum rpm if you are not going to run the engine that fast?

There is another point to consider: the 375 hp engine should be more efficient than the 355 and should probably burn less fuel at the same speed...but I would not consider that.
Since I understand Tobnpr is not considering cost in his decision I would go for the power boost at least for the feelgood factor and because power is never enough when you consider that just a little fouling of the hull will completely destroy all of our calculations...
 
osd9 said:
40 pony upgrade- worth it?

...the only difference is...now you won't be able to make the rated WOT RPMs....you would be overpropped.

What's the difference between propping for the extra HP and re-calibrating the fuel/timing delivery for the extra HP? Wouldn't both motors be doing the same work at the same RPMs...just doing it differently? I'm sure the answer is simple, and I have my own thoughts, but I'm really kind of stuck on this one-......
Click to expand...

Had to read it a couple of times, and I'm still not sure I'm understanding the heart of your question.
It sounds like you're asking "What's the harm in overpropping?"
Any means of turning the same size prop at the same rpms in the same boat will result in the same speed- no?

We all know that overpropping kills diesel engines quickly. While both engines are producing the same power, the overpropped engine is running too hot with too much boost and dumping fuel in an attempt to make power- that it can't...

It's like starting to drive your car up a hill in third gear.
 
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Can you post your ser# prefix and performance spec #? I'de like to look at this some. ...Ron
 
Not sure if this "really" relates or not, but I did bunch of work on a 5.9 liter Cummins engine I had in a Dodge I had a while back. It was mainly in the injector pump timing, turbo, etc. The "fix" was mainly in how much fuel was injected and the timing of it. I had to add a new intercooler because the increase in fuel and fuel pressure raised the exhaust gas temps a great deal. If I was putting a heavy load on it, for a length of time (several mile long uphill grade) , the EGT would start creeping up then stay for quite a while - sometimes bumping the edge of the red zone. I see the same thing happening with over-propping.
 
Keep in mind that I am talking about motors that are designed by the manufacturer's engineerr to be tuned-up in HP with NO iron differences....not just hot rodding or shad-tree mechanicing some extra boost because you can......

Here's another way of looking at it....let's back in to it.......let's say you have the 350HP motor I described above....and it's not making the rated 2800 WOT RPMs.....well, in order to not be overpropped for the 350HP motor, you would have to re-do the props....then your cruise speed at the rated 2400 RPMs would go down. OR...you could retune the motor to give more HP and then with the same props you would make the rate 2800 WOT and your cruise speed at the rated 2400 cruise RPM would remain the same.....
 
tobnpr said:
Had to read it a couple of times, and I'm still not sure I'm understanding the heart of your question.
It sounds like you're asking "What's the harm in overpropping?"
Any means of turning the same size prop at the same rpms in the same boat will result in the same speed- no?//.
Click to expand...

But they are not.....the motor rated at 350 HP will have to be propped differently (less pitch) in order to reach the rated 2800 WOT RPM then the motor that is rated at 390 HP....so at the same rated cruise speed of 2400 RPM, the 350 HP boat will have a slower cruise speed because it's props have less pitch....
 
osd9 said:
Here's another way of looking at it....let's back in to it.......let's say you have the 350HP motor I described above....and it's not making the rated 2800 WOT RPMs.....well, in order to not be overpropped for the 350HP motor, you would have to re-do the props....then your cruise speed at the rated 2400 RPMs would go down. OR...you could retune the motor to give more HP and then with the same props you would make the rate 2800 WOT and your cruise speed at the rated 2400 cruise RPM would remain the same.....
Click to expand...

All true.
Re-prop an "overpropped" boat to be correct and the cruise speed will drop.
Increase the HP so the engine now has the power to spin the original prop (that was too large) and the cruise speed remains the same as it was in the overpropped condition- except now the engine is no longer overloaded because the fuel delivery, timing, blah, is correct for the horsepower you're asking the engine to produce at any given rpm.

But I still don't see the question; so I'll bail in deference to those smarter than I :)- guess it's been too long a day.


Ron, the ser #'s are 01Z05...
Supposedly the instructions for the upgrade are covered in special instruction SEHS8586, which is good for engines with s/n's 01Z04500 and up- or so I've read. Got to contact Ring Power to see if I can get a copy.

What is a performance spec #- is it on the engine plate?
 
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That's exactly my question and what I'm discussing....and trying to figure out....

Why would the same motor...with the same internals....same cooling system....same turbo...same everything i.e. all the same iron...EXCEPT for a tuning of the fuel delivery system, all of sudden be overloaded in one configuration and not in the other? That's what I can't wrap my small brain around....

Wouldn't you be asking all that same iron to make the same heat and stress at the same cruise RPMs with the same props?

Been a long day here too I guess!!!
 
Not pretending to be a diesel expert here, but the extra fuel is where the heat comes in. Most of the motor upgrades you see on the street- some of which are making 900+ foot pounds of torque (in extreme cases) dump a huge amount of fuel- which makes more power- remember the air mixure does not change- just the fuel volume and pressure.
 
Chris....I agree...but the retuned motor is the one dumping in more fuel, and making more heat, then the overpropped motor....but it's the overpropped motor that is overloaded....again...we're talking about at the rated cruise speed of 2400 RPMs....
 
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