Gear box hp

[fatboy0054]

Need to the formula to figure hp and pounds from the gear box at the hub . I always thought like a 2.37 to 1 would be double the hp with about .37 percent lost in action of tranfer ,but been told different .Didnt belive , but anyway . I wanted the motor heads to let me know which tree am I looking up or do I find another tree . thank sirs

 

[jim]

Fatboy,

I hoped that someone would answer this that could give you an estimate or measurement of the power loss of a 2.37. I'll give you the theoretical answer and get this back to the top.

The HP at the prop flange on a gearbox will be less than the HP at the flywheel due to the friction losses in the gear box. A similiar comparison would be flywheel HP vs rear wheel HP in a car.

The gearbox will multiply the torque less the friction loss in the manner you described.

Jim

 

[fatboy0054]

Thank you sir

 

[Waterthunder]

Just as already stated take you’re torque and multiply it by your gear ratio. Say you have a nasty small block that makes 500 Ft Lbs of torque and you run a 2.68to1 gearbox you just multiply 500Lb’s X 2.68ratio=1340 Ft Lb’s of torque here is the tricky part gear reductions are not very efficient the manufactures state different numbers for efficiency losses. No matter what they say the physics of it is the higher the torque multiplication the less efficient a gear box is in other words a 2to1 box is more efficient than a 2.38 or 2.68. I have heard from several gearbox manufactures that an average of 37% loss is good for a 2.68 and an average of 32% loss is a good number for a 2to1.

 

[T-REX]

thunder how does the gearbox effect horsepower ?

 

[Anonymous]

T-Rex,

TQ is force, and HP is just the calculation of work done. A high HP engine that revs higher will make more HP, but possibly less TQ. A gearbox multiplies that torque, at the expence of frictional/heat losses. But when you use a more efficient engine that makes much more HP, the losses are far outweighed. In simple terms....If we build a 470ft# small engine that turns 6000 and another guy builds a 600ft# engine that turns 3000, and we multiply the TQ with a 2:1, on paper we are making 940 TQ minus 30% (Stricktly an overstatement to do the math) we still are making 658....Of course we make much more power than that and the gearboxes are much more efficient than that...The real deal.....HP when used properly is KING...Just my opinion.

Felber

 

[Waterthunder]

If you don't run a gearbox you will not make any horsepower because your engine will not be able to turn any RPM's. The higher the gear ratio the more RPM's your engine can turn before your prop tip's become supersonic so the higher ratios allow your engine to develop more horsepower. It all inter relates. Everybody get’s misguided by one main theory as in torque is all that matters or build a motor that make torque at low RPM’s or build a motor that makes HP at low RPM’s. Well Felber is right HP is king but in an airboat we need to develop it sooner and generally when you do that a motor develops higher torque numbers. However if you only shoot for the big torque numbers then you have a terd of a motor above 4,000RPM so why bother running a gear box. I build broad airboat engines that are efficient and generate power and torque across a wide band of RPM’s and I know that’s the best way to build an airboat motor. It’s a hell of allot easier to just shoot for peak torque numbers or peak HP numbers to impress people but a broad well designed motor will kick either ones ass every time. The down fall is most people fall for marketing and buy what puts up big numbers even though the motor is a terd everywhere else. I have learned this from Felber let everybody else throw around B.S. peak numbers and Horsepower numbers and concentrate on just building a better broader motor. In the end the broader better designed motor will always perform better.

 

[Eshoberg]

I'm pretty new to this but the loss on gearboxes surprises me. On my ls1 car I lose about 12 to 14% hp going through a 6spd tranny in 4th gear with a 1:1 rate. The loss on an a gear reduction is 3 times that?

 

[jim]

That number surprised me too. A 37% loss means that if the engine has 600 hp at the flywheel, it only has 378 hp at the prop!

Jim

 

[Anonymous]

In my uninformed opinon the thing that a lot of folk tend to overlook in this argument about horsepower and gearboxes, car motor vs. aircraft
engine, is that it all comes down to one word ..... purpose.

I run a 350 SB Chevy on my old boat, turnin' a Franklin belt drive. The engine is nothin' fancy. It's your basic 350 with an Edelbrock intake and carb (they used to call them Carter AFB's), and a set of headers. It is very reliable, easy to fix, parts are considerably less expensive compared to a Continental or Lycoming, and it does my job.

The point is that it probably makes about the same horsepower as an 0540 (260-300) if Im willing to spin it's guts out. The 0540 is happy as a clam at 2400rpm and could reasonably be expected to give you well in excess of 1500 hrs. of reliable service operating in that range. My little 350 on the other hand would have to live at 4800 rpm for the same amount of time in order to give you comparable performance. That ain't likely to happen.

BF

 

[Waterthunder]

If it was built to run in an airboat it would live that long. I have seen several V/8's with over a thousand hours of reliable service. Most of the car motors in my area live longer than the aircrafts.

 

[Anonymous]

Thunder, your point is well taken, and I'm not opening this discussion to find fault. My point is that in the argument of aircraft vs. auto engine, I don't think that we're always comparing apples to apples.

We've all seen comparisons of the weight of a 350 Chevy and an 0540 Lycoming because they're both touted to be 300 horsepower engines, and the 0540 really doesn't have that much of a weight advantage even though the Chevy has to have a radiator, coolant, hoses, etc.

But if we factor in longevity, and my engine is evaluated on the
RPM range where it can not only be expected to live a long time but also to return some reasonable gas mileage, then in truth I'm probably only runnig around with about 200 horsepower most of the time. Now the weight comparison shifts to a much smaller aircraft engine (something like an 0360?) and then the aircraft engine's "purpose of design" begins to really show.

Am I about to dump my little Chevy for an A/C engine? No way! I love the ease of maintenance and the cost to maintain it. But I resist the notion that we can directly compare the two different types based strictly on horsepower.

This is where what you do becomes important ..... you're getting big horsepower numbers and tons more reliability out of the same engine block as mine, and I admire that. I'm lookin' forward to having you build one for me one of these days I just think that we sometimes mislead when we base performance numbers between the two types strictly on horsepower.

BF

 

[Waterthunder]

It all depends on what you want your boat to do. I love burning up the hill and I have found aircraft motors do not run the hill with two or three people as well as a car motor that’s why you don’t see any tour boats with 0-540's on them. When it comes to pushing weight or generating max thrust a car motor is my favorite. If you want to frog or ride alone you can’t beat a 180 or 160 if you want to run with 2 people and like aircraft motors you can’t beat a 0-540 if your on a budget you cant beat a 220gpu or a DD car motor. Nothing on this earth is the best at everything. Arguing car motor vs aircraft is about as dumb as arguing Ford vs Chevy or Dodge. Each application requires a different answer. Each motor has it’s strong points and it weaknesses!

 

[Anonymous]

I think we understand the discussion now, Thunder, and I'm glad. I wasn't throwin' off on the auto engines you build ..... far from it.

Up here where Ann and I run, we seldom if ever run the hill. We boat in deep water most of the time (there's a hole in the lake that we live on that the depth finder says is 168' .... probably an old spring), and it ain't any big deal to be in 50' water.

I carry one of those styrofoam buoys in my boat (the kind that crabbers use) with 100' of line on it. The idea is that if I sink this old barge of mine one of these days, the buoy will float to the surface and mark the spot so I can go back and try to retreive it.

I blew up on the shore a couple of times to hide-out when a storm came up, but runnin' dry is something that never comes up.

BF

 

[Waterthunder]

That’s one area I must admit an aircraft is superior. When you sink an airboat and have to pull it up the aircraft is much easier however the worst is a deck in car motor boat now that made for a miserable experience.