Cruising speed rpm?

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BGREEN427
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Re: Cruising speed rpm?

Post by BGREEN427 » Tue Jul 26, 2016 10:27 pm

You gained 80# torque on 17 cubic inches and lost 20 hp. That is a head scratcher for sure.

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Re: Cruising speed rpm?

Post by SWAMPHUNTER45 » Tue Jul 26, 2016 10:59 pm

Failed Logic

If your point was correct (which it is not) every engine dyno sheet would produce the same torque yield at the same horsepower output.



OneBFC wrote:
SWAMPHUNTER45 wrote:Yep Deano that ole 514 roller Cadillac on a 1:53 vs a sbc on a 2.55 is a great example of torque vs horsepower.
Realize that both caddy and SBC setups have to make the same Horsepower to move the boat the same speed (let's ignore weight for the moment).

So it isn't really Torque vs hp.

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OneBFC
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Re: Cruising speed rpm?

Post by OneBFC » Tue Jul 26, 2016 11:11 pm

I don't follow your point, can you explain?
SWAMPHUNTER45 wrote:Failed Logic

If your point was correct (which it is not) every engine dyno sheet would produce the same torque yield at the same horsepower output.



OneBFC wrote:
SWAMPHUNTER45 wrote:Yep Deano that ole 514 roller Cadillac on a 1:53 vs a sbc on a 2.55 is a great example of torque vs horsepower.
Realize that both caddy and SBC setups have to make the same Horsepower to move the boat the same speed (let's ignore weight for the moment).

So it isn't really Torque vs hp.
-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
Life begins at 2 BAR, Just a good ole boy

jeepinocala1111
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Re: Cruising speed rpm?

Post by jeepinocala1111 » Wed Jul 27, 2016 6:39 am

http://blog.caranddriver.com/horsepower ... ifference/

This might be a simple way to explain the difference.

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OneBFC
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Re: Cruising speed rpm?

Post by OneBFC » Wed Jul 27, 2016 12:23 pm

Jeep i dont know if your reply was meant for me or just general info for all. That article says exactly what I am saying as well.
-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
Life begins at 2 BAR, Just a good ole boy

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Re: Cruising speed rpm?

Post by kwanjangnihm » Wed Jul 27, 2016 12:40 pm

Guys I would like to know which one to choose myself. I would opt for the higher torque if the horsepower is the same, but I need someone to tell me why that is or is not a better choice.
" 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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OneBFC
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Re: Cruising speed rpm?

Post by OneBFC » Wed Jul 27, 2016 2:27 pm

Guys I would like to know which one to choose myself. I would opt for the higher torque if the horsepower is the same, but I need someone to tell me why that is or is not a better choice.
Quite a complicated thing to answer unfortunately. The info you listed for each engine is incomplete.

This was originally a cruise RPM thread and I feel bad for diverting attention from the original topic.

If anyone really wants to continue discussing engine hp/tq, etc, perhaps a new thread would be best. I'll leave this as my parting bit of info I generated back when I was using a 100% stock engine setup, not the larger turbo I run today.

https://docs.google.com/spreadsheets/d/ ... sp=sharing

This shows what data I collected on my particular setup. Some of the data is physically measured, some of it is obtained from digital gauges and a small bit is calculated via formula.

Black line = Propeller Thrust (measured physically)
Blue line = Required engine Torque (From digital gauges)
yellow line = Available engine Torque (From GM engine dyno data)

The more shaded yellow area you have in this type of graph, the more "snap" you will have. You can plot a chart like this for any engine if you have accurate dyno data for it. You will also need a matching information for the propeller you want to use that lists required propeller shaft torque for a given propeller RPM. Coincidentally, propeller manufacturers do not provide those for some reason......I had to obtain this info from physically measuring the thrust on my boat. This fact makes it exceedingly hard to compare propellers between manufacturers and match them to engines in a mathematical (ie: exact) way.

I am quite sure that some people like Dave at WT have a mountain of data like what I posted above to be able to match an engine to a propeller correctly. No agenda for me on any of this, not trying to convince anyone X engine with Y prop is better than any other. I just enjoy this as a hobby and want to see future generations enjoy it as well.

If anyone really wants to continue this side discussion, pop another thread up and I'll join there.

Oh, Cruise RPM for my particular boat is around 2200 skinny water at 25mph to about 2700 to 2800 deep. Boat weighs 2000lbs fueled up and loaded with cooler and 2 people (measured, not a guess).
-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
Life begins at 2 BAR, Just a good ole boy

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Re: Cruising speed rpm?

Post by Bdriller » Wed Jul 27, 2016 2:49 pm

I was without stating it implying that good low cruise numbers are going to be achieved by pitching the prop as much as possible at the desired cruise rpm, in order to do this the engine will need to be at a fairly high torque number at that rpm and if cam selection is decent you can still hit a max rpm that is acceptible , thus good cruising, jmo but at cruise im gona pic higher torque over higher hp.

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Re: Cruising speed rpm?

Post by CarMotorBarge » Fri Jul 29, 2016 3:39 pm

The high torque supporters need to look at "Sheet1" on the spreadsheet that Russ provided. The "Thrust to Prop RPM (Theoretical)" graph shows how the thrust changes as prop speed increases. I have thrust data from Dave's thrust tester and I can tell you that the shape of the thrust curve from Dave's thrust tester matches the graph in Russ's spreadsheet.

The spreadsheet also contains the "HP to Propspeed" graph. What is interesting here is that the shape of this curve matches the "Thrust to Prop RPM" curve. However, this is expected because it takes HSP to turn the prop.

Ultimately what is interesting about both of these graphs is the shape of the curve. As you go from left to right along the curve, the curve doesn't go up linearly. This curve is called an Order N Squared curve in Computer Science. The concept is that an increase of 2 units from left to right causes an increase of 4 (2 squared) from bottom to top. An increase of 10 units from left to right causes an increase of 100 (10x10) from bottom to top. Basically as you go from left to right along the curve, the curve increases at a sharper rate.

The shape of the prop thrust curve implies that you need substantially more HSP to go from 5000 to 5100 engine RPMs than from 3000 to 3100 engine RPMs. So if you want to turn as much prop as possible, you have to make decent torque and good HSP at higher engine RPMs. Ultimately this prop thrust curve is why a properly setup LS, BBC, SBC will turn more prop than an A/C or Caddy.

What is also interesting about the 2.68 ratio is that you have additional flexibility than lower gear ratios such as a 2.0 or 2.38 when turning wide or super wide blades. What I mean by this is that you can turn the engine 5400 RPMs with 2.68 and make really good thrust or you can add pitch and turn the motor only 4800 to 5000 RPMs and gain 10% to 20% better fuel mileage. So you can have the best of both worlds with the 2.68. We just need the prop manufacturers to come out with a prop that allows the driver to change the prop pitch on the fly. 8)
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OneBFC
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Re: Cruising speed rpm?

Post by OneBFC » Fri Jul 29, 2016 5:05 pm

Yep, some good info in this spread sheet. I found it very helpful.

I updated the charts on sheet 1 slightly to show a 3rd order polynomial trend line with a r^2 of 0.99 (ie: nearly perfect fit) that shows that if the setup we tested to obtain that data was able to turn the prop 2200 RPM it would require 400HP and it would produce 1600lbs of thrust.

Perhaps this is why my ecoturd does fairly well with the bigger turbo :) I think I agree with JR that a 2.68, or near that, would be a good fit with engines that can achieve peak power near 5600RPM. A stock LHU/LNF Ecotec will make peak power at 5200 to 5300 and worked well with the 2.38 due to this. Jeff's LTG Ecotec peaks at a higher 5500 or 5600 so a 2.68 is probably best.

Anyway, sure looking forward to getting back to airboating....trying my hardest to find the time.
-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
Life begins at 2 BAR, Just a good ole boy

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Cruising speed rpm?

Post by JLACOUR » Fri Jul 29, 2016 9:50 pm

I run a 16x8 diamondback deck over with a stock LSA. 83" 4 blade sensenich (set at position 2, or 9.48 on the digital angle finder) 2.52:1 reduction and turn 3300-3400 cruise deep water with 2-3 people and coolers. Cruise speed is 35-36 mph. Max rpm is about 5600rpm.
Last edited by JLACOUR on Mon Aug 01, 2016 11:42 am, edited 1 time in total.

SWAMPHUNTER45
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Re: Cruising speed rpm?

Post by SWAMPHUNTER45 » Fri Jul 29, 2016 11:36 pm

I have seen a few good DD 400 sbc engines
Last edited by SWAMPHUNTER45 on Sat Jul 30, 2016 8:08 am, edited 1 time in total.

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Re: Cruising speed rpm?

Post by CactusJack » Sat Jul 30, 2016 1:16 am

I would think the 400 small block would be a better DD motor and the 383 a better gearbox motor. From my experience with 400's they like to push, not be geared down. If you plan on using a gearbox, go the 383 is my opinion
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Re: Cruising speed rpm?

Post by CarMotorBarge » Sat Jul 30, 2016 7:33 am

OneBFC wrote:Yep, some good info in this spread sheet. I found it very helpful.

I updated the charts on sheet 1 slightly to show a 3rd order polynomial trend line with a r^2 of 0.99 (ie: nearly perfect fit) that shows that if the setup we tested to obtain that data was able to turn the prop 2200 RPM it would require 400HP and it would produce 1600lbs of thrust.

Perhaps this is why my ecoturd does fairly well with the bigger turbo :) I think I agree with JR that a 2.68, or near that, would be a good fit with engines that can achieve peak power near 5600RPM. A stock LHU/LNF Ecotec will make peak power at 5200 to 5300 and worked well with the 2.38 due to this. Jeff's LTG Ecotec peaks at a higher 5500 or 5600 so a 2.68 is probably best.

Anyway, sure looking forward to getting back to airboating....trying my hardest to find the time.
I definitely don't think a 2.68 is the best ratio for all motors. Ultimately the ratio should be based on the type of prop, the targeted prop RPM at WOT, and the targeted engine RPMs at WOT. I wouldn't use a 2.68 on an A/C or a Caddy. I also wouldn't use a 2.68 for an LS turning a DD prop such as an NGQ.

What I am saying is that you want to maximize the HSP at the targeted engine RPMs at WOT. This is how you maximize the amount of prop turned by the combination. Maximizing the torque at WOT will push the HSP too high in the engine power band and the combination will not turn as much prop at WOT. Ultimately, you don't care what the torque curve looks like when selecting a motor. You don't even need to see the torque curve. However, you do care what the HSP curve looks like because it tells you how much prop you can turn at the targeted WOT.

BTW, I would pick the 383 over the 400 based on the currently available data. :stirpot: :stirpot: However, the HSP curve of both engines is needed to make the final decision.
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kwanjangnihm
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Re: Cruising speed rpm?

Post by kwanjangnihm » Sat Jul 30, 2016 2:20 pm

Russ can you explain the 2 constants in these columns?

Column B 2.68 - this appears to be a gearbox ratio to calc prop rpm
Column E 2.37 - is this your 2.37 gearbox on your boat now, or a torque calc constant?

I also like how you setup the theoretical & measured thrust.

I am still ingesting the data you presented and how it correlates to HP, Torque & Thrust! Great job!! :thumbleft:
" 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: Cruising speed rpm?

Post by Bdriller » Sun Jul 31, 2016 11:22 am

Bdriller wrote:well heres one yall can fuss about I have two choices on a motor, number 1 is 383 cui. 500hp 480 torque #2 choice is 400 cui. 480hp 560 torque now which one do you think is the right choice with 2.7 gear? I realise a sounder decision could be made if both dyno sheets were made available but I cant see where this is not a no brainer.
sorry guys this was a typo, it was revealed when the actual dyno sheets arrived so for those of you that thought this was impossible you were correct. The actual peak numbers on the 400 were 525 torque @ 4200 and 480 hp @ 5800 rpm.

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