Motor Reliablity

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Moritz
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Re: Motor Reliablity

Post by Moritz » Wed Jul 20, 2016 10:11 pm

Wedge is installed typical run is 1800 # with full fuel

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Re: Motor Reliablity

Post by CarMotorBarge » Thu Jul 21, 2016 6:38 am

Dr. Russ,

You forgot about friction in the gearbox. Otherwise your numbers look spot on. 8) This spreadsheet shows why a 2.68 ratio will always turn more prop than a 2.38, 2.55, etc. Assuming the cam is correct, the 2.68 lets you get to more HSP.
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Re: Motor Reliablity

Post by CarMotorBarge » Thu Jul 21, 2016 6:46 am

Moritz wrote:Wedge is installed typical run is 1800 # with full fuel
You can try taking the wedge out, but these hulls are flawed from the manufacturer. So I have a few more questions. Sorry that I keep asking, but there are no easy answers here. How low is the back of the engine? Can you post several pictures of the boat? How old is the hull and poly? Are there any dents in the bottom of the boat. Especially look at the back 8 feet of the boat.
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Re: Motor Reliablity

Post by SWAMPHUNTER45 » Thu Jul 21, 2016 8:07 am

The other element to consider and acknowledge is that every platform has it's own individual strength and weakness. We can learn from our experienced engine builders as it relates to a specific platform. As an example WT Dave the LS master has observed that the 2.68 ratio on a properly built LS engine will reduce stress and allow the engine to live long beyond a 1,000 hour service life. A contrasting example would be Mr. Branch a Cadillac builder will recommend to his clients run as small a ratio as possible and load the engine. There are many a Branch engine that goes over 1000 hours or 10 years in both gear drive or direct drive airboat use also.

These stark comparisons are made just to state that one particular way of doing things is not universal. Pick a builder who is a master of his platform with a great reputation and get your order in writing with the specific components promised listed on the invoice. This will go a long way to ensure your expectations and happiness with the build.

Just one other comment: In the past month I have seen 2 machine shop Cadillac rebuilds come thru the Branch shop, brought in by customers who put their engine on and it would not run right. With the first some of the rod bearings were installed improperly blocking off oil flow and giving the engine a death sentence. On another the machine shop put 500 pistons on a 472 crank which made for an excessive quench. Other substandard parts were used and to put it simply these fellows got engines that will not live very long because they were assembled by builders unfamiliar with the platforms.

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Re: Motor Reliablity

Post by Olf Art » Thu Jul 21, 2016 9:12 am

OneBFC wrote:This has been beat to death so many times. I sure hope I don't regret posting what I'm about to say. There are MANY simplifications taken for granted here, please don’t beat this up on semantics, OK? Also, not trying to “start” anything here. If you think I am wrong, please show me. If you want to just say “you’re wrong” and not back it up, you are only going to embarrass yourself. IF I am wrong and you can prove it, I’ll be the first to admit my error and concede to your superior mind :)
Turning a prop isn't about horsepower or rpm. It's all about torque
The above quoted statement is, unfortunately, wrong.

Now, if you have an engine that you want to use with Propeller A and you want the propeller to turn 3000 RPM, you will need the engine to produce 600 lb-ft of torque, at the prop shaft, when the propeller shaft is turning 3000 RPM. This is most likely pretty obvious still and I can hear the "no sh*t..." from here eve Commonly people use Gear boxes, belt drives, etc to do this. Of course this is more “No Sh*t”, just hang in there.
*
Good grief .... what a pile of horse sh*t this is. Whoever taught you all of this did you a real dis-service. Nowhere in this diatribe is any discussion about piston speed or stress on the reciprocating components. The subject at hand is reliability, and an engine that will run reliably for years on end and without a lot of attention.. Some hot rod little squirt sitting on top of a big gearbox might do the job right now, but don't look for it to be worth more than scrap metal twenty years from now.
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Deano
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Re: Motor Reliablity

Post by Deano » Thu Jul 21, 2016 10:11 am

Doesn't matter who wrote:. . . This spreadsheet shows why a 2.68 ratio will always turn more prop than a 2.38, 2.55, etc. . .
This is absolutely, undeniably correct. :thumbleft:
Doesn't matter who wrote:. . . Assuming the cam is correct, the 2.68 lets you get to more HSP. . .
This is absolutely, undeniably wrong. Gear ratio does NOT "get more HSP".
Gear ratio WILL allow you to "get more TORQUE", which is exactly why the first statement is true.

How many times have you heard/read WaterThunder Dave say/write that "a gearbox is a torque multiplier" ?

In spite of his view, I appreciate Russ' hesitance to broach this subject matter because there are just enough semantics involved that the debate has and will likely continue to rage on, due to misconceptions and the repetition of inaccurate statements made like the one above.

It is somewhat amusing, and somewhat disheartening both, that such inaccurate statements and fundamental lack of conceptual understanding are what fuel this needless ongoing debate because another inquisitive newbie reads that and it makes sense to him, so he repeats it, and on and on and on.

Like Swamphunter pointed out, you can turn a big prop with authority using the platform of your choice as long as you are delivering the prerequisite required torque to the prop shaft. That is the only requirement. As Russ pointed out and then even demonstrated in his earlier thread, if a prop needs x amount of torque to spin it x number of rpms, it does not give a damn about the horsepower of the engine on the other side of the gearbox.

You can use BIG torque x small gear (which may last longer) -or-
You can use small torque x BIG gear. Either way can work equally well out of the gate.

Which ever way you choose to do it, the measure of the energy converted to thrust by the prop is measured as torque at the prop shaft.
Last edited by Deano on Thu Jul 21, 2016 10:22 am, edited 2 times in total.
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Re: Motor Reliablity

Post by John Fenner » Thu Jul 21, 2016 10:16 am

Remove the polymer wedge, take a straight edge to bottom and use an 18" crescent wrench to bend overhanging lip down until it doesn't rock the straightedge.
When they weld the transom plate to the bottom, it pulls that lip upward causing the porpoising.
I never finish anyth,,,.

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Re: Motor Reliablity

Post by Moritz » Thu Jul 21, 2016 12:39 pm

po;y is 3 years no dents the boat does not run on the noze

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Re: Motor Reliablity

Post by jeepinocala1111 » Thu Jul 21, 2016 1:03 pm

CarMotorBarge wrote:
Moritz wrote:Wedge is installed typical run is 1800 # with full fuel
You can try taking the wedge out, but these hulls are flawed from the manufacturer. So I have a few more questions. Sorry that I keep asking, but there are no easy answers here. How low is the back of the engine? Can you post several pictures of the boat? How old is the hull and poly? Are there any dents in the bottom of the boat. Especially look at the back 8 feet of the boat.
I will have to say you are wrong stating these hulls are flawed I see a lot of trim tabs, bent edges, and other things to keep from porpoising and will say all of these hulls are not flawed they may have to be changed for weight distribution or other things to keep from needing one of these quick fixes but flawed is the wrong word. I have seen the same exact hull with the same motor but one with more power and one bounces around where the other keeps the nose up.

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Re: Motor Reliablity

Post by Duece » Thu Jul 21, 2016 3:23 pm

Holy crap, there's like 3 conversations going on here???

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Re: Motor Reliablity

Post by Des Moines Boater » Thu Jul 21, 2016 4:03 pm

I may be a little slow but I still have no idea why I have a 2.7 drive instead of a 2.3 or a 2.5. What should I use for max rpm and what should I cruise at. I bought the boat with a 2 to 1 drive and a wood prop and it did all right but I wanted it to be better and quieter.
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Re: Motor Reliablity

Post by Waterthunder » Thu Jul 21, 2016 5:49 pm

Funny story I had two guys in my shop telling me that a 2.55 performs better than a 2.68. Very broad statement as mentioned earlier in this post about one ratio being the best. my 1st response was on what motor. I have a lifetime of racing and engine building in my back ground. Not to mention I was involved with designing a protype plane from the ground up. So I know no one set up is the best for everything I believe everything is rooted in simple physics.

Anyway these guys didn't care about logged dyno thrust sheets that are so accurate a 5mph wind will make significant changes not to mention relative humidity and corrected altitude. Any way we ran a 550HP motor with a 2.68 ratio with a 82" 10 blade saber we set the prop to turn 5,600 then after we got exactly 5600RPMs we shut the motor off and swapped the 2.68 for a 2.55 and bolted the prop on all withing 40 minutes and made a pull. The prop and motor combo lost 430 RPM's.

So after debating this for hours I just looked at the 2 guys and said you know if your right you need to go home and take out pitch and set your prop to turn 430rpms less because according to you it will run better. You know I THINK THE WERE FINALLY ABLE TO GRASP THE CONCEPT.

Years ago everyone thought a 2.68 was harder on a motor, I told everyone its easier on a motor to turn a few more RPM's than it is to over load it. I use the truck full of rocks theory. Load a truck down with rocks and try an start in 2nd gear you will detonate the motor to death but put it in low and its a piece of cake.

So my moto became use your gearbox as a torque multiplier not a RPM enabler. The next thing is keep adding pitch to that 2.68 you will not have what a few people preach is a optimum "tip speed" but you only loose a 100lbs of peak thrust at wide open. Which I spend less than 1% of all my running at wide open, however you will pick up to 80lbs of thrust at cruise which is where we all spend most our time. Everyone wants something a little different but for the majority of the time a 2.68 with a big prop is the way to go. And yes we have tested 2.88 and 3.21 ratios I think at that time you become a fat kid pedaling a bicycle down hill. The inefficiencies become to much to have any mechanical advantage. Oh yea do some testing and monitor gearbox oil temps that was a crazy debate that nobody wanted to hear the results.
THE PROOF IS IN THE PROP!

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Re: Motor Reliablity

Post by Des Moines Boater » Thu Jul 21, 2016 6:29 pm

My question on the 2.7 to 1 I have is, what should my max RPM be and what should I cruise at?
It just seems odd to me that with a 2.7 @ 5200 RPMs, I'm not even turning the prop at 2000 RPMs. The new NGR is rated to 2800 RPMs. I could never get close to that with my 383 SBC. The lower rpm is quiet though. I'll listen to the experts like Water Thunder but I don't fully understand the rationale. My set up seems to work.
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Re: Motor Reliablity

Post by CarMotorBarge » Thu Jul 21, 2016 11:01 pm

Deano wrote:
Doesn't matter who wrote:. . . This spreadsheet shows why a 2.68 ratio will always turn more prop than a 2.38, 2.55, etc. . .
This is absolutely, undeniably correct. :thumbleft:
Doesn't matter who wrote:. . . Assuming the cam is correct, the 2.68 lets you get to more HSP. . .
This is absolutely, undeniably wrong. Gear ratio does NOT "get more HSP".
Gear ratio WILL allow you to "get more TORQUE", which is exactly why the first statement is true.

How many times have you heard/read WaterThunder Dave say/write that "a gearbox is a torque multiplier" ?

In spite of his view, I appreciate Russ' hesitance to broach this subject matter because there are just enough semantics involved that the debate has and will likely continue to rage on, due to misconceptions and the repetition of inaccurate statements made like the one above.

It is somewhat amusing, and somewhat disheartening both, that such inaccurate statements and fundamental lack of conceptual understanding are what fuel this needless ongoing debate because another inquisitive newbie reads that and it makes sense to him, so he repeats it, and on and on and on.

Like Swamphunter pointed out, you can turn a big prop with authority using the platform of your choice as long as you are delivering the prerequisite required torque to the prop shaft. That is the only requirement. As Russ pointed out and then even demonstrated in his earlier thread, if a prop needs x amount of torque to spin it x number of rpms, it does not give a damn about the horsepower of the engine on the other side of the gearbox.

You can use BIG torque x small gear (which may last longer) -or-
You can use small torque x BIG gear. Either way can work equally well out of the gate.

Which ever way you choose to do it, the measure of the energy converted to thrust by the prop is measured as torque at the prop shaft.
I think you need to read the scientific definition of torque and how it relates to work (horsepower). Here is a good link:

https://en.wikipedia.org/wiki/Torque

Torque is the rotational force that accelerates the prop. Horsepower is what measures the distance that the prop turns over time. The prop does care what the horsepower the engine is making. This is why a 300 HSP A/C motor turns less prop than a 600 HSP car motor. Put whatever gear ratio you want on the A/C motor and it will always turn less prop than the 600 HSP car motor using the correct gear ratio.

The gearbox "torque multiplier" allows an engine to "get to more HSP". You misquoted me and left out the word "to". The gearbox doesn't change the HSP curve of the engine, but it does allow the engine to generate enough RPMs to "get to more HSP". It also doesn't allow you to "get more TORQUE". Take Dave's example above about going from a 2.68 to a 2.55. The engine made more HSP at 5600 RPMs versus 5170. That is why it turned more prop. However, assuming a normal airboat torque curve (torque tops out around 4800 RPMs), the engine possibly will make more torque at 5170 than 5600. So the lower torque (even with the torque multiplier) at 5600 RPM actually turned more prop.

Here is another way to think about why HSP matters and torque doesn't. Take a motor with maximum torque at 4800 RPMs and maximum HSP at 5400. Using a 2.68 gearbox, the motor will produce more thrust at 5400 RPMs than using a 2.68 gearbox at 4800 RPMs and more pitch in the prop. The torque at 4800 RPMs will be higher, but more thrust is produced at 5400 RPMs because the HSP is higher.
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Re: Motor Reliablity

Post by Moritz » Thu Jul 21, 2016 11:21 pm

toque is the product of force times distance. same as 600 ft when you torque a bolt.

when you multiply by how fast (RPM) you get power.one horse power = 550foot pounds per second.

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Re: Motor Reliablity

Post by CarMotorBarge » Thu Jul 21, 2016 11:33 pm

Torque is the force only. It doesn't include the distance. HSP adds how fast. To calculate how fast, you need distance and time.
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Re: Motor Reliablity

Post by Moritz » Thu Jul 21, 2016 11:51 pm

by distance I mean the distance between the force and the center of rotation

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Re: Motor Reliablity

Post by Moritz » Fri Jul 22, 2016 12:07 am

the distance traveled on one revolution the is the distance from the center to the force time 2 time 3.14-distance around a circle - circumference

so you multiply force #'s by distant ft time 2 time 3,14 time the rpm a divide 33000(units are ft # per minute) and you get horse power.
force times distance from center of rotation to force is equal to torque

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Re: Motor Reliablity

Post by SWAMPHUNTER45 » Fri Jul 22, 2016 5:38 am

5250 Rule

If your getting the job done at 5250 rpm or below your doing it with raw torque, if you exceed 5250 then horsepower is the relevant driving force after that point. At least that was the theory explained to me as we select components. In the end the words of WT Dave ring through "the proof is in the prop!"

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Re: Motor Reliablity

Post by rbjscott » Fri Jul 22, 2016 8:59 am

"What make and who build a the most reliable motor in the 650 to 750 hp. One that will run 1000 hours with out failure" Mast Motor ports engine would be my choice. And they are close.
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Re: Motor Reliablity

Post by Deano » Fri Jul 22, 2016 12:09 pm

I am well aware of the definitions of Torque and HP. It's odd that you would reference one of the same sources that I would refer you to. :lol: Quite obviously more HP will do more work, since HP is in fact a measure of work done. No one ever said or implied that HP was not relevant and that torque was all that mattered.

What I was trying to convey is that, in this case, for our purposes of turning a prop, torque is the measure of the force being applied to do the work. As you maintain, HP is the measure of the work being done over time.

In spite of which side of the Torque/HP debate one starts at, HP is by definition. . . a measurement of Torque over time. Mechanical horsepower is defined as 550 ft/lbs per second which is the basis for the formula with which you are familiar: HP=(Torque x RPM) /5252.

If you have no torque, you will have no HP. However, you can have torque and not HP. Torqueing down head bolts is just one example. Torque is the rotational force applied, whether it is a head bolt or a flywheel or a prop shaft.

So we are both using different verbage to arrive at the same conclusion. In the beginning of this thread, when Olf Art said it was all about torque, I understood that he was referring to the longevity of the subject engine and not making a generic statement that applied across the board like Russ evidently thought he did.

To use the example from your above post:
CarMotorBarge wrote:Here is another way to think about why HSP matters and torque doesn't. (You can not have HSP without first having torque) Take a motor with maximum torque at 4800 RPMs and maximum HSP at 5400. Using a 2.68 gearbox, the motor will produce more thrust at 5400 RPMs than using a 2.68 gearbox at 4800 RPMs and more pitch in the prop. The torque at 4800 RPMs will be higher, but more thrust is produced at 5400 RPMs because the HSP is higher.
Given peak torque is @ 4800. This also means that peak efficiency of this given engine occurs at that rpm. In spite of more thrust possibly being available beyond that, the premise is simply that the engine would last longer if it were setup and pitched to turn 4800 instead of 5400. Furthermore, if the prop and gear where optimally chosen to peak at the same 4800 rpm, turning it up to 5400 may or may not result in the gains that you assume are there to be had, sometimes that is not the case. While how much 225 prop rpms (with decreased pitch) would alter max thrust may vary, what is for sure is that with a 600 rpm increase in engine rpms it will use more fuel, endure more stress and generate more wear.

When a person is after efficiency and longevity from the engine, he might well do himself a favor by viewing the dyno graph like the torque curve is plotting engine efficiency and the right half of the HP curve as representing fuel consumption. This is why a long, flat torque curve is so desirable. I also agree with Dave's premise that a small percentage of total time is spent at WOT, so that is of little consequence to me.

At least for my purposes, I would readily sacrifice some rpms at WOT and make my gear and prop selections such that it may never see peak HP, but rather was operating the majority of time in the higher areas of the torque curve. I believe it will run more efficiently and do so for longer.
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Re: Motor Reliablity

Post by Moritz » Fri Jul 22, 2016 11:27 pm

lets get back to motor reliability

lets try this a different way for big blocks only
How many hours do you have on your motor since New, HOW many cubic inch, what have you had to replace or what failed

I will start off
530 hours 454 bored and stroked to 496 cubic inches fuel pumps 3 failure, distributor 3 ,roller bearing in lifter taking out cam /oil pump /bearing rod and main/ baffles broken in oil pan/ head gasket. next failure of strap that keeps lifter from rotating, 3 sting gear box failure 2 were broken input shaft 2,68 , one was teeth broken on shaft 2.54 and 1 QX DRIVE INPUT SHAFT 2.68

Looking at used boats I do see many with a lot of hours , A lot have just a few since rebuilt or new motor put in.

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Re: Motor Reliablity

Post by rbjscott » Sun Jul 24, 2016 2:33 pm

ZZ 502 has 550 hrs no failures did have ignition wires break down. Replaced dist. with MSD billet HEI. Carb to a built Holley from SS performance
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