502 power VS torque

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digginfool
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Re: 502 power VS torque

Postby digginfool » Thu Feb 22, 2018 12:22 pm

loudmouse wrote:Carmotor, I would be interested seeing ur same thrust test repeated with a 4 blade JX to see if it requires more or less hp to make same or more thrust. As you approached MBT, you Gained 200 lbs in several hundred (300) rpms. This is typical of a engine that's built for performance not economy.


It would be even more informative if it was matched with the dyno sheet on the engine. It would be interesting to see how thrust correlates to engine output.
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Re: 502 power VS torque

Postby kwanjangnihm » Thu Feb 22, 2018 5:27 pm

CMB - How were the R's pitched for the above thrust graph?
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Re: 502 power VS torque

Postby Deano » Thu Feb 22, 2018 5:28 pm

I comment here only to prevent confusion among those trying to make sense of all this and gain understanding, not to take sides or even join in the debate. As much as I do not want to offend my esteemed colleague, it will help prevent confusion and speed comprehension of this subject to be aware that the following statement is fundamentally incorrect.
previous poster wrote:. . . The shape of this thrust curve applies to all props. This includes DD and reduction props. The only item that changes is the amount of thrust that is made at each RPM. . .
The more correct statement would be that "The shape of this thrust curve shows the characteristics of this SET OF BLADES with the change of thrust at each RPM, being proportional to the changes in available power".

It should be readily observable that no single thrust curve would apply to all props.
To sight an extreme example for ease of illustration, compare a Warp Drive prop to a Super Wide prop.
WD is terribly inefficient down low, but after it's wound up to a point, it is very efficient.
SW excels at pushing down low, but when wound up to a point, it's efficiency goes downhill fast.
No way these two thrust curves would look the same.

The thrust curve that is posted (or any other for that matter) is the propeller equivalent of a torque curve posted from engine dyno.
- in other words -
The torque curve (produced by the dyno) graphically shows how ENGINE design characteristics are influencing the engine performance.
The thrust curve (produced by the thrust tester) graphically shows how the BLADE'S design characteristics are influencing the thrust performance.

With that basic understanding, there are a couple other things that become self evident.
First, each different blade design (or prop model) will have it's own unique Thrust Curve based on it's design characteristics.
Second, different props are MOST efficient at different RPMs, hence, their thrust curves will display differently, reflecting that reality.

Ultimately, (dependent on intended use) the design goal should be to match the engine's power band to the prop's thrust curve.
Having these numbers (or graphs) in hand, simplifies attaining that end when you get outside of your preexisting experience.

------

On a different note, but perhaps also worth noting is that a graphed thrust curve will more easily lend itself to prop comparisons when it is labeled in PROP rpms, rather than engine rpms. It's understood, that wasn't the intent when that was made for the boat's owner. Only meaning to eliminate another point of potential confusion for those in the learning mode. (ie. the gear ratio, as a variable is eliminated)
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Re: 502 power VS torque

Postby Slidin Gator » Thu Feb 22, 2018 6:42 pm

CMB, thanks for the prop curve, I have put together some graphs using this curve to further explain my point. For these curves, I used the WOT thrust and RPM data point (1,860 lbs thrust at 5,350 engine RPM) and back calculated the rest of the curve using a simplified Y^2 formula. So it does not exactly match the whole Thrust vs. RPM curve, but it’s just an example after all. I also converted this over to prop RPM using the 2.68 gear ratio cited as suggested by Deano.

Now, for the torque side, this is all straight OOMY (Out Of My Axle). I just assigned a reasonable prop torque value for the 1,860 lbs thrust value and back calculated as a linear function. So, the actual numbers may/will not match any specific prop. I also totally agree with Deano’s statement that this curve will look different for different props. This is just your typical imaginary prop.

Walking through the charts, the first page shows the linear thrust vs. torque relationship that I have stated. In this case, RPM is not shown, specifically to illustrate the torque relationship. Different props do have different characteristics.

Chart #2 shows the prop curve (rescaled from CMB’s graph) in red. The blue line represents prop torque vs. RPM – at steady state. Here I am selecting 1,500 Prop RPM as the operating point at steady state. The prop generates 1,100 lbs of thrust, which correlates to 750 ft-lbf at 1,500 RPM steady state.

The final 2 charts show 2 different engine/gear setups with different WOT (wide open throttle) torque characteristics. Both of these curves run out to the same 1,290 ft-lbf of torque and 2000 RPM. Setup A has an idealistic, flat torque output between 1,200 and 2000 RPM. Setup B has a heavily sloped torque curve, peaking at 1,290 ft-lbf.

I then show the potential thrust that each set up will produce immediately if operating steady state at 1,500 RPM and the throttle is opened to WOT. Setup B (Orange Dots) is the easiest one to use to explain the markings. Draw a horizontal line from where the Orange torque curve crosses 1,500 RPM, which shows setup B producing 1000 Ft-lbf at 1,500 RPM at WOT. The blue prop torque curve crosses 1000 ft-lbf at about 1,800 RPM. Draw a vertical line there to cross the prop thrust curve at 1,400 lbf of thrust.
So Setup B, operating at 1,500 RPM, has an immediately available thrust range from 1,100 to 1,400 lbf of thrust. As the engine spins up, the thrust will climb to 1,860 lbf at full speed. If the conditions dictate 1,400 lbs of thrust, the operator will have to back off the accelerator some to keep thrust constant. Otherwise, the system will spin up and over run what is really needed.

In comparison, Setup A, operating at 1,500 RPM, has an immediately available thrust range from 1,100 to 1,860 lbf due to the flat torque characteristics. In order to hit 1,400 lbf of thrust, the operator does not need to use WOT, just enough throttle. This platform will exhibit a much flatter response with little to no accelerator adjustment required to hold 1,400 lbf of thrust as the rig spins up. Prop speed will also stabilize at 1,800 RPM vs. over running to 2,000.

Please realize that this are all simplified curves, your experiences may vary. There are a whole range of setups that can perform along the lines of Setup A with a flat torque curve. In the old days, it was a choice. These days there are many options to have both (or at least a lot closer to it). Boosted engines are great for producing flat torque curves and Injected engines with proper tunes and components can achieve similar performance, all without making major sacrifices to peak thrust capability. But it is also possible to really kill overall performance by focusing too much on a single, peak HP figure and not paying attention to matching up the whole system.
Attachments
Prop Torque Curves.pdf
(700.22 KiB) Downloaded 39 times
I grew up thinking I-10 was the Mason Dixon line.
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Re: 502 power VS torque

Postby CarMotorBarge » Fri Feb 23, 2018 6:36 am

loudmouse wrote:Carmotor, I would be interested seeing ur same thrust test repeated with a 4 blade JX to see if it requires more or less hp to make same or more thrust. As you approached MBT, you Gained 200 lbs in several hundred (300) rpms. This is typical of a engine that's built for performance not economy.


Remember that the prop doesn't know what is turning it. The gaining of 200 lbs in several hundred RPMs wasn't caused by the performance characteristics of the engine. This was caused by the torque requirement of the prop. My entire point is that the performance characteristics of the engine have to be tuned to satisfy the props torque characteristics if you expect to turn more prop.

Also this "performance engine" on a 5 seat barge gets 3 MPG under typical riding circumstances. The boat is in my signature. 8)
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Re: 502 power VS torque

Postby CarMotorBarge » Fri Feb 23, 2018 6:37 am

kwanjangnihm wrote:CMB - How were the R's pitched for the above thrust graph?


Thanks for fixing the picture. I knew you would have my back. 8) Also the prop was pitched from 2.5 to 3.
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Re: 502 power VS torque

Postby CarMotorBarge » Fri Feb 23, 2018 6:51 am

Deano wrote:I comment here only to prevent confusion among those trying to make sense of all this and gain understanding, not to take sides or even join in the debate. As much as I do not want to offend my esteemed colleague, it will help prevent confusion and speed comprehension of this subject to be aware that the following statement is fundamentally incorrect.
previous poster wrote:. . . The shape of this thrust curve applies to all props. This includes DD and reduction props. The only item that changes is the amount of thrust that is made at each RPM. . .
The more correct statement would be that "The shape of this thrust curve shows the characteristics of this SET OF BLADES with the change of thrust at each RPM, being proportional to the changes in available power".

It should be readily observable that no single thrust curve would apply to all props.
To sight an extreme example for ease of illustration, compare a Warp Drive prop to a Super Wide prop.
WD is terribly inefficient down low, but after it's wound up to a point, it is very efficient.
SW excels at pushing down low, but when wound up to a point, it's efficiency goes downhill fast.
No way these two thrust curves would look the same.

The thrust curve that is posted (or any other for that matter) is the propeller equivalent of a torque curve posted from engine dyno.
- in other words -
The torque curve (produced by the dyno) graphically shows how ENGINE design characteristics are influencing the engine performance.
The thrust curve (produced by the thrust tester) graphically shows how the BLADE'S design characteristics are influencing the thrust performance.

With that basic understanding, there are a couple other things that become self evident.
First, each different blade design (or prop model) will have it's own unique Thrust Curve based on it's design characteristics.
Second, different props are MOST efficient at different RPMs, hence, their thrust curves will display differently, reflecting that reality.

Ultimately, (dependent on intended use) the design goal should be to match the engine's power band to the prop's thrust curve.
Having these numbers (or graphs) in hand, simplifies attaining that end when you get outside of your preexisting experience.

------

On a different note, but perhaps also worth noting is that a graphed thrust curve will more easily lend itself to prop comparisons when it is labeled in PROP rpms, rather than engine rpms. It's understood, that wasn't the intent when that was made for the boat's owner. Only meaning to eliminate another point of potential confusion for those in the learning mode. (ie. the gear ratio, as a variable is eliminated)


I agree that I didn't do a good job of explaining this. I was writing this in a hurry just before I went to work. 8) All I was trying to point out is that all prop thrust curves have a quadratic nature to the shape of the curve. Prop thrust does not increase linearly as prop RPM increases. This quadratic nature has a direct impact on where you want the engine torque applied to the prop thrust curve.

Another way to explain this is to look at a compounding interest calculator online. Put $1000 in at year 0. Assume 10% interest a year. The first year the interest is $100 (assuming interest is accumulated only once a year). The interest in year 10 will be more than $100 because of the compounding nature.
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Re: 502 power VS torque

Postby CarMotorBarge » Fri Feb 23, 2018 7:11 am

Slidin Gator wrote:CMB, thanks for the prop curve, I have put together some graphs using this curve to further explain my point. For these curves, I used the WOT thrust and RPM data point (1,860 lbs thrust at 5,350 engine RPM) and back calculated the rest of the curve using a simplified Y^2 formula. So it does not exactly match the whole Thrust vs. RPM curve, but it’s just an example after all. I also converted this over to prop RPM using the 2.68 gear ratio cited as suggested by Deano.

Now, for the torque side, this is all straight OOMY (Out Of My Axle). I just assigned a reasonable prop torque value for the 1,860 lbs thrust value and back calculated as a linear function. So, the actual numbers may/will not match any specific prop. I also totally agree with Deano’s statement that this curve will look different for different props. This is just your typical imaginary prop.

Walking through the charts, the first page shows the linear thrust vs. torque relationship that I have stated. In this case, RPM is not shown, specifically to illustrate the torque relationship. Different props do have different characteristics.

Chart #2 shows the prop curve (rescaled from CMB’s graph) in red. The blue line represents prop torque vs. RPM – at steady state. Here I am selecting 1,500 Prop RPM as the operating point at steady state. The prop generates 1,100 lbs of thrust, which correlates to 750 ft-lbf at 1,500 RPM steady state.

The final 2 charts show 2 different engine/gear setups with different WOT (wide open throttle) torque characteristics. Both of these curves run out to the same 1,290 ft-lbf of torque and 2000 RPM. Setup A has an idealistic, flat torque output between 1,200 and 2000 RPM. Setup B has a heavily sloped torque curve, peaking at 1,290 ft-lbf.

I then show the potential thrust that each set up will produce immediately if operating steady state at 1,500 RPM and the throttle is opened to WOT. Setup B (Orange Dots) is the easiest one to use to explain the markings. Draw a horizontal line from where the Orange torque curve crosses 1,500 RPM, which shows setup B producing 1000 Ft-lbf at 1,500 RPM at WOT. The blue prop torque curve crosses 1000 ft-lbf at about 1,800 RPM. Draw a vertical line there to cross the prop thrust curve at 1,400 lbf of thrust.
So Setup B, operating at 1,500 RPM, has an immediately available thrust range from 1,100 to 1,400 lbf of thrust. As the engine spins up, the thrust will climb to 1,860 lbf at full speed. If the conditions dictate 1,400 lbs of thrust, the operator will have to back off the accelerator some to keep thrust constant. Otherwise, the system will spin up and over run what is really needed.

In comparison, Setup A, operating at 1,500 RPM, has an immediately available thrust range from 1,100 to 1,860 lbf due to the flat torque characteristics. In order to hit 1,400 lbf of thrust, the operator does not need to use WOT, just enough throttle. This platform will exhibit a much flatter response with little to no accelerator adjustment required to hold 1,400 lbf of thrust as the rig spins up. Prop speed will also stabilize at 1,800 RPM vs. over running to 2,000.

Please realize that this are all simplified curves, your experiences may vary. There are a whole range of setups that can perform along the lines of Setup A with a flat torque curve. In the old days, it was a choice. These days there are many options to have both (or at least a lot closer to it). Boosted engines are great for producing flat torque curves and Injected engines with proper tunes and components can achieve similar performance, all without making major sacrifices to peak thrust capability. But it is also possible to really kill overall performance by focusing too much on a single, peak HP figure and not paying attention to matching up the whole system.


Thanks for generating the PDF file. This is making for an interesting discussion. 8) In the interest of having an even better discussion, can you make the following changes to either of the last 2 charts:

1. Can you change the torque line (black line) for setup A so that it shows 1290 foot lbs from 0 prop RPM to 2000 prop RPM? This will be a perfectly flat torque curve.

2. Can you change the torque line (orange line) for setup B so that is shows 990 foot lbs at 0 prop RPM and increases linearly to 1590 foot lbs at 2000 prop RPM? This torque curve will represent pushing torque to higher RPMs (moving the torque curve to the right on a dyno sheet).

3. Can you add a third torque line (setup C) that shows 1590 foot lbs at 0 prop RPM and decreases linearly to 990 foot lbs at 2000 prop RPM? This torque curve will represent pushing torque to lower RPMs (moving the torque curve to the left on a dyno sheet).

I understand that this graph isn't realistic. This is just a theoretical discussion. 8)
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Re: 502 power VS torque

Postby Slidin Gator » Fri Feb 23, 2018 9:33 am

Set ups C, D and E added. Note that I came up with the torque figures by assuming an engine torque of 600 ft-lbf at 5,350 RPM at the engine, then decreased that by an 80% efficiency value for the gear box. I think the engine torque is high and perhaps the gear box efficiency is better.

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Attachments
Prop Torque Curves Rev A.pdf
(778.63 KiB) Downloaded 15 times
I grew up thinking I-10 was the Mason Dixon line.
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Re: 502 power VS torque

Postby kwanjangnihm » Fri Feb 23, 2018 12:03 pm

Slidin Gator I added the charts to your post! :thumbleft:
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Re: 502 power VS torque

Postby Slidin Gator » Fri Feb 23, 2018 12:23 pm

Thanks Kwan, I saw you did that with the original torque curve and was going to ask you how to do that, but it was too late to bother last night.

Can you give a run down on how to post pics directly into the post? Perhaps a different thread on the subject would be useful.
I grew up thinking I-10 was the Mason Dixon line.
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Re: 502 power VS torque

Postby nolaboat » Fri Feb 23, 2018 1:24 pm

Well guys I can say with confidence that Im more confused now than Ive ever been. lol But really its good info you guys are giving. A little about the boat. It was a stock 21ft dixie airboat with a lycoming 0-540. 200hp. That sounds why under powered to me. Not looking for speed. I just want to drive up and over land when needed. I knew adding a big block with all the weight I needed to produce a certain amount of power over the weight. To get the power I need will determine how much money I need to drop in the engine. Once I get the power I will work the #'s you guy gave to pick out witch gears and prop i need. A lot of good info guys. Thanks.

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Re: 502 power VS torque

Postby Slidin Gator » Fri Feb 23, 2018 3:05 pm

Nola,
I think page 1 of this thread covered this pretty well and the general agreement is that you want more of everything, more power, more torque and more prop. An O-540 is a great motor, but it's way outmatched by your requirement! Can we assume that you started this thread asking about a 502 because you have one or access to one, or are you more open to other motor options?

You made one statement here that I suggest you reconsider:
Once I get the power I will work the #'s you guy gave to pick out witch gears and prop i need.


It is best to work the problem from the opposite end, figure out which prop (or class of prop) best fits your application, then figure out an engine and gear combination to best match the prop. If the engine is already a given, then you are down to figuring out the gear and engine build needed to match.

In your case, a dry running, 21 foot boat is going to need a lot of prop. Start by weighing the rig as it is now. Add/subtract weight to account for a full fuel tank, people and all the gear you plan to haul. The 4:1 thrust and 8:1 power ratios BFC gave you are good guides to use as a starting point, and more is better. For the prop you want to go as big in diameter as you can buy and fit to your set up. Increasing prop diameter (all else being equal) will give equivalent thrust at lower speed, higher torque. The net will be less power for the same thrust, or more thrust for the same power, as long as torque is accounted for with gearing. My example of an infinitely long prop producing infinite thrust with no power was intended to illustrate this point in the extreme.

The trade off with the larger prop is a decrease in top speed since you are pushing more air, but at a lower exit velocity. Everything is a trade off, but I assume that dry ground running is more important for you than top end. You might even think about a counter rotating prop set up, you can gain on the order of 30% thrust due to improved efficiency, but of course the set up is more complicated. Start a new thread on that subject if interested, some of the tour boats here in Fla. run CR set ups.

You are still in the 700+Hp range, but here is where I go against the grain (again) and stir the pot. If the object was no money (or is it money is no object? I think they are the same), I would look into a turbo diesel build. I'm speaking out of my axle a bit here since I have not looked into any of this in detail, but a big block, cast iron gas motor has to weigh something getting close to the newer diesels with aluminum heads and intakes. Quick figures that come up on google show an LS7 at ~450 lbs. I'm going to guess 700-800 lbs (or more) for an Iron big block dressed to go. A new stock Ford Power stroke is around 970 lbs (dry) and makes 440 Hp at 2,800 RPM. Peak torque is 860 ft-lbs at 1,600 RPM and torque is pretty flat with a max power rating of 440 Hp at 2,800 RPM, which is 820 ft-lb. These engines have plenty of options available for pushing power well beyond 700 Hp and the diesel forums seem to say they take it well. Just deleting the EGR system and changing the tune on those engines perk them up significantly. Even if the diesel adds 300 lbs to the set up, that's not so much of a hit on a 21 foot boat. Using the 8:1 ratio as a guide, that's 40 more Hp required to match 300 lbs more weight. Of course there are a lot of marine diesel options out there too.

In any event, a 21 footer with turbos whining while mowing the field and blowing black smoke would be a cool rig for sure! It would be economical to operate, but it would be a learning curve and money pit to build. Lear jet engine anyone?
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Re: 502 power VS torque

Postby SeatCover » Fri Feb 23, 2018 10:37 pm

T 53 turboshaft lycoming. Lol. Really though a few diesel boats are running the hill. Look on YT, Rollin coal like crazy.
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Re: 502 power VS torque

Postby nolaboat » Sat Feb 24, 2018 6:49 pm

Slidin gator. Thanks again. Ur rigjt about the 502. I have 2 of the from a boat. Sending one off in two weeks to start the rebuild. I do have a ls2 ready to go but didnt think i would work well in a 21ft boat. Funny u say diesel. I say one with a duramax in it. I do have access to a few diesel engine and two good friends of mine are diesel rebuilders. But like u said. Maybe another build down the road. Just want to get one up and running. QUESTION. is this a good site to post 0-540 lycoming for sale? I know new orleans is a little far.

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Re: 502 power VS torque

Postby CarMotorBarge » Sat Feb 24, 2018 7:40 pm

Slidin Gator wrote:Set ups C, D and E added. Note that I came up with the torque figures by assuming an engine torque of 600 ft-lbf at 5,350 RPM at the engine, then decreased that by an 80% efficiency value for the gear box. I think the engine torque is high and perhaps the gear box efficiency is better.

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Thanks for posting the updated charts. Now it is time to talk about which of the 3 torque curves require the driver to mash the pedal to the floor the most often when driving. I understand the 3 torque curves are completely made up, but this is just a theoretical discussion. 8) :

Prop RPM below 1,000 RPMs: Setup C (green line; high torque down low) will have to mash the gas less than the other 2 setups. Setup B (orange line; high torque up high) will have to mash the pedal the most out of the 3 setups. However, the prop torque requirement is so low under 1,000 RPMs that none of the motors have to floor it to accelerate the prop several hundred RPMs.

Prop RPM above 1,000 RPMs: Setup C (green line) will have to mash the gas the most. Setup B (orange line) will have to mash the gas the least. Also here is the kicker. Setup C will turn the least amount of prop and Setup B will turn the most prop. Moving torque higher in the RPM band is why geared car motors always turn more prop than A/C. :stirpot: :stirpot: :stirpot: :stirpot: :stirpot: :stirpot: :stirpot: :stirpot: Why would somebody want to turn a car motor into an A/C motor by moving the torque down low. :shock:
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Re: 502 power VS torque

Postby Slidin Gator » Sat Feb 24, 2018 7:44 pm

Re: 502 power VS torque
Postby nolaboat » Sat Feb 24, 2018 6:49 pm

Slidin gator. Thanks again. Ur rigjt about the 502. I have 2 of the from a boat. Sending one off in two weeks to start the rebuild. I do have a ls2 ready to go but didnt think i would work well in a 21ft boat. Funny u say diesel. I say one with a duramax in it. I do have access to a few diesel engine and two good friends of mine are diesel rebuilders. But like u said. Maybe another build down the road. Just want to get one up and running. QUESTION. is this a good site to post 0-540 lycoming for sale? I know new orleans is a little far.


When you are trying to sell something, more advertisement is better than less I'm pretty sure! But yes, this is definitely a good site to advertise it on, there are folks from all over the place on here and there appears to be enough of ya'll La. boys that check in here to make it worth while. I think Mud Motor Talk is pretty popular for your neck of the woods too. Those Mud Motor jockeys are all tired of man handling those motors and secretly dreaming of an airboat! I know, that used to be me!

The funny thing is that it looks like I will be in and out of S. La. starting in May for about a year. I plan to haul my boat out there and will be looking for folks in the area to show me around, you can never have enough friends in the woods and all. I will also be looking to haul some dogs with me for hunting opportunities.

In any event, I might be able to save some one the freight if it gets down to it.
Last edited by Slidin Gator on Sat Feb 24, 2018 7:50 pm, edited 1 time in total.
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Re: 502 power VS torque

Postby CarMotorBarge » Sat Feb 24, 2018 7:48 pm

nolaboat wrote:Slidin gator. Thanks again. Ur rigjt about the 502. I have 2 of the from a boat. Sending one off in two weeks to start the rebuild. I do have a ls2 ready to go but didnt think i would work well in a 21ft boat. Funny u say diesel. I say one with a duramax in it. I do have access to a few diesel engine and two good friends of mine are diesel rebuilders. But like u said. Maybe another build down the road. Just want to get one up and running. QUESTION. is this a good site to post 0-540 lycoming for sale? I know new orleans is a little far.


You need to determine how many RPMs that you plan to turn the 502 at WOT. This will determine where you want the max HSP to come in and what gear ratio to use. Remember that the maximum recommended prop RPM on superwide blades is lower. Wish you the best. 8) Also the reason this thread got so much attention is because the title contained "power VS torque". This is like the A/C versus car motor debate. :stirpot: :stirpot: :stirpot: :stirpot:
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Re: 502 power VS torque

Postby SWAMPHUNTER45 » Sun Feb 25, 2018 6:51 pm

No debate come see torque live and in person.
Was out today with a fellow airboater we came across a Whites 632 BBC dyno at 850hp same ratio drive with less ability than my antique.
Hey maybe I have more horse power than I think. Lol

Torque

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Re: 502 power VS torque

Postby oleman » Mon Feb 26, 2018 9:02 am

After riding with you with both the "old antique Caddie motors" I can honestly say that you definitely have a lot more horsepower than you think. Back in the day when I net fished for mullet we all ran 20' airboats both glass and aluminum hulls carrying 1000 yards of net, ice, gear, and 2000 lbs of fish. Motor of choice ... Caddies, why because they had the torque to swing the big paddle props necessary to bring the load back home running on top. Wasn't a question of hp but of torque. High hp BBC boats didn't cut the mustard. Many times had to help "them out" by hauling half their fish plus mine back in for them so they could get on top with the other half and not bog home. By the way nearly all the Caddies we used came straight from the junkyard to the boat and never made a pass by Mr Branches or anyone else's shop for any improvements. Made a believer out of me.
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Re: 502 power VS torque

Postby kwanjangnihm » Mon Feb 26, 2018 9:37 am

SWAMPHUNTER45 wrote: come see torque live and in person

" I don't care who you are back in the world, you give away our position one more time, I'll bleed ya, real quiet. Leave ya here. Got that? "

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Re: 502 power VS torque

Postby nolaboat » Mon Feb 26, 2018 10:39 am

Ok guys another question for the class. I have an older Rotator gear. Theses are the only #'s on it. R600 10R212H. What am i looking at? Im planning on using as part of my build if I can but not sure of the reduction ratio.

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Re: 502 power VS torque

Postby SWAMPHUNTER45 » Mon Feb 26, 2018 11:01 am

2.12 if never altered

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Re: 502 power VS torque

Postby nebraskaairboater » Mon Feb 26, 2018 1:04 pm

Check with Classic / Panther... if it isn't the wide gear model you may have more power than it can handle.
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Re: 502 power VS torque

Postby Slidin Gator » Mon Feb 26, 2018 9:35 pm

I have had time to look into some 502 build option specs. In particular the following two web sites have dyno test data for different build configurations:

http://www.fourwheeler.com/how-to/engine/131-9809-gm-performance-parts-502-torque-motor-buildup/
http://www.chevrolet.com/performance/crate-engines

The Four Wheeler link shows results from several builds, including a high RPM, High HP version. The following graph shows torque curves for these builds plus the Chevy crate motor specs:

Image


Out of these options, the 2 torque curves that look like they have the most potential are the Chevy Crate ZZ502 and the Four Wheeler 502 Version 3A build. For comparison, the ZZ502 would be a “Torque” motor build and the Version 3A would be a “Horsepower” build. The interesting thing that I note is that the “Horsepower” build actually makes a little more torque than the “Torque” build, plus it makes that torque at a lot higher RPM, so it makes a lot more power.

If anyone has any other input on torque curves for this engine, please add them to the thread.

I applied 3 different gear ratio options to these two engine options, the 2.12 Nola has, a 2.68 and a 2.88 ratio. I also used a 90% efficiency reduction factor on the gear box. This is just a guess on my part and I am open to any input on what a good figure to use here would be. Some of the discussions I have seen on this subject said that gear box efficiency varies a lot and is hard to predict, but that should be part of the discussion.

Image


This 21 foot boat application needs to throw the largest diameter prop possible. So this will need an 82” (or even bigger) prop with a maximum RPM in the range of 2,300 to 2,500, but you can run them slower, particularly with more blades, as others have noted here.

The first thing that this makes clear is that the 502 does not make the kind of torque or power that everyone has said this application needs. So it is going to be tough to make this 21 footer run dry. Looking at these curves, it looks like the 2.12 ratio box on hand is not enough gear to turn a big prop.

From my view, the 2.88 ratio and a high Hp build looks like the best, or probably only way to go, especially given the desire to run dry (because it is an airboat after all, it needs to run dry). That puts the motor operating above 4,000 RPM for most of the time, so make sure the heads and valve train gets the attention that it needs.

One note of caution, none of these sources provided torque data in the lower RPM region and the HP motor curve show the torque going flat below 4,500 RPM. If that is the case, then it is as close to perfect for the application as possible, but I wonder if these are really valid figures. Since this boat will be marginal at best on ground, it is going to need as much torque as possible off the line to get started on ground.

The end result is a big prop, turning at or below 2,000 RPM and a motor that operates in the 4,500+ RPM range. Talk to the motor builder and see what they have to say about maintaining good torque (~ 500 ft-lbs) below 4,500 RPM. If you have to sacrifice some top end torque to keep the low end flat, that would be a tradeoff to consider.

One last point, do note that the “Torque” curve is a factory crate spec engine while the “HP” curve is an aftermarket tuned unit. If this motor can be built to make substantially more torque down low, the above should be re-accessed.

How about some input to solve this riddle.
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