You realize you answered your own question don't you?

 

Not exactly.

Other's may be satisfied with their mowers with lesser HP, because the Hydros don't consume as much engine HP, deck design = less clogging in heavy grass, blade lift consumes less HP, etc...

I guess I should always add, that the WHY / CONTEXT behind the answer, is always more important than just a quick answer itself.

 

It's always better to have too much horsepower than not enough, 25 is fine for flat, ideal conditions 30 is better

 

i politely disagree

unless your planning to regularly use the extra power, wouldnt having a larger engine simply just be an extra upfront cost, and cost you more in gas overtime? because then you just have to slow down a bit in case you run into tough conditions.

 

The faster you want to cut grass, the more HP you need. One of my Walkers is a 52” and has a 16hp. Although I prefer a bit more hp, I can’t complain. It’s never been an issue. But I also understand the deck design and what it’s capable of. It isn’t a speed mower, nor am I looking for it to be. If I wanted to mow at lightening speed, I wouldn’t run Walker. The vacuum mowers have a 21 and 23 respectively. I would never say overkill, but with 48” decks they don’t work very hard.

Hydro’s are HP robbers period. You lose between 15 and 20% through the hydro to the ground regardless.

 

I would not have wanted less HP than my 31 Kawi 921 on my 61 Cheetah. But with my 61 V-ride, using the identical cutter deck, my 25 Kawi 801 is more than enough (at least in my opinion). My new one will have a Kawi 38.5 hp motor, reasons that I won't bore you with, but not because I need more power.

 

I listed 25 hp for 2 main reasons.
#1 for a 60" mower 23hp would be lacking for power .
#2 Minnesota is passing a law that new sales of anything under 25 hp
will have to be electric. Starting 01/01/2025.

 

I listed 25 hp for 2 main reasons.
#1 for a 60" mower 23hp would be lacking for power .
#2 Minnesota is passing a law that new sales of anything under 25 hp
will have to be electric. Starting 01/01/2025.

If California falls into the ocean, how is Minnesota going to follow that?

 

I ran a 62 inch deck on my 20 HP walker. It cut grass, just not very tall grass. But worked great if you stuck to the 1/3 rule.

 

Which in all honesty is what the Walker is designed to do. It isn’t meant to cut overgrown grass, even though in the spring I consistently have to do it. 62” is a belt drive deck. They handle tall stuff better than the timed decks do.

 

I have found that 5 HP per foot of deck width is plenty sufficient for most mowing conditions, 6 HP per foot of deck width if mowing in tough conditions (i.e. tall & wet turf, lush overgrown weeds, steep slopes) or if you are mowing every two weeks. For those of us mowing weekly, 5 HP per foot of deck width will just about cover all the bases.

 

What's the minimum engine horsepower that you'd be satisfied with on a 60" commercial mower?

I've littered the board with posts about buying a 2nd 60" mower - stander or ZTR.

I see a lot of machines with 23, & 25hp engines.



My current machine is a 29hp Kohler EFI, which is actually around 26.5hp under the new/current spec. Quite often, I want more horsepower. Especially when making turns, taking off, and/or starting up hills.

I find that I don't mind slowing down as much for heavier/taller grass. If I had more HP to power-through faster, I'd overwhelm the (eXmark) deck, and get a poor cut anyway.



What's the minimum engine HP you'd consider on a 60" mower. (Current rating spec which new machines abide by.)

really depends, but for weekly cutting 23 hp is plenty. expecially on exmarks. they offer a 23.5 hp engine on their 60" standers now and in none of the reviews ive seen on it have there been a lack of power. then again, its top speed is only 9.5 MPH

generally, for just mowing weeklys, 23 or 25 HP is plenty, but if your planning to run a bagger, mulch leaves, or have the ability to cut yards really fast then bump up to 30 HP engines.

 

More power is always better than not enough. The engine doesn;t have to work as hard to do the same amount of work, so may actually use less fuel since you may not end up in the governor near as much. The hydros will have more available to run them without taking from the deck. etc

 

LOL- we posted the same thing at the same time

 

I had a lawn business for 25 years and owned a lot of different 60" mowers. I also owned a lawn equipment store for several years and sold a lot of 60" mowers. In my opinion, for most conditions, 23HP is enough. However, 25HP is better. Anything over 25HP is pretty much not needed. This is just my opinion.

 

You probably remember when the old SCAG 3 wheel mowers came with a 18 HP Kohler and a 61 inch deck.

Cut grass plenty good, but they had a geared transmission, used a lot less HP to just propel the mower

 

My vote is for 25. 23hp is fine but if i had to pick the cutoff id say 25. I mow a lot of open area at 10mph or faster so cant be crawling with underpowered mower or i would lose too much time.

 

I have a grasshopper with a 27 never had any issues with hills or anything has over 2000 hrs going strong. Bigger debate gas vs diesel have a gh 225d much faster more torque better economy. Both are great for normal mowing and can do over grown but prefer the diesel for those.

 

Well, if we're going to be scientific about it, the larger engines won't be consuming more, or less fuel than the smaller engines. (Keeping this within the context of mowing.)

Both the larger & smaller engines are going to be running at 3,600rpm, +/- a few. Hydros & decks will be spinning at the same speed. = same work being done, and/or energy being consumed.


The difference will be - once you "load" the engines, which one will dropp/lose RPM's the most? The smaller engine of course.

One the load is applied to the engines, the governor will open the throttle plate to keep engine speed at 3,600rpm. The difference then, is that the weaker engine will reach max load / wide open throttle plate much sooner.

Only if you continue to load the larger engine with more work/load, will it then begin to consume more fuel.





This is where the debate really STARTS. Which is more fuel efficient - Running the smaller engine at max load for longer? Or running the larger engine for less amount of time?

The answer to that question, is that the larger engine will let you finish the job sooner. You may even be able to reduce RPM and thus save fuel if you wanted. And what I mean by that, is reduce engine RPM (becuase the engine has adequate power to turn the blades a little slower, without bogging the engine down,) and maintain the same ground speed via a little extra motion from the hydros.

 

And RE Gas vs. Diesel, and Torque vs. HP - This argument of "the diesel engines will have more torque" is a lie.
1hp = 33,000 ft/lbs of work per minute. Always has been, always will be.

Long story short, if you look at any dyno-graph, of any engine ever made (that can reach this RPM anyway) the HP and Torque are ALWAYS EQUAL at 5,252rpm.

What does this mean? Horsepower is simply a mathematical function of Torque x RPM.

If the Gas & Diesel engines for our mowers are both goverened for a 3,600rpm working speed, then they will effectively produce the same Torque at 3,600rpm as well.

If the diesel engine is really MORE powerful than the gas engine, then it's because someone is lying on the specs & ratings. But mathematically, it cannot produce more torque, than a gas engine, at the same HP & RPM rating...

 

Here we go again. This is such a bunch of BS. You do not even remotely have any understanding whatsoever of HP/Torque ratio. I'm not going to debate you again about it, but you are incorrect. You are mixing up information with a lack of understanding.

 

All I know is the 40 HP diesel on my 21" outperforms the 14 HP gasser on my 72" machine........................

 

Why do horsepower and torque cross at 5,252 rpm?

We've talked in the past about the relationship between horsepower and torque. They work together, and horsepower needs torque to make you and your car happy. There's one magic number though that doesn't get much ink spilled its way, virtual or otherwise. The number is 5,252, and it's the point...

www.motorauthority.com

 

The fact of the matter is that what Jashley is saying is proven true, it's factual information. If there's an argument then it needs to be done so with information to back that up.

 

I don’t have the time at present to give a detailed response.

@Jashley73 go find the horsepower/ torque data of the Kubota WG900 and the Kubota D900 and post that data. When I have time I’ll come back. A dyno graph like above would be great if you can find it.

 

The closest examples that I can find seem to be the current D902 900cc diesel, WG972 972cc gas engines.

(If you want to make a finer point with your two previous examples, I'll have to ask you to provide those documents, because I'm not sure I'm willing to commit a whole lot more time to find them.)



Analysis - Though it's not a true apples-to-apples, diesel vs. gas engine comparison per the same CC, the gas engine produces A LOT MORE HP/liter, and torque per liter than the closest diesel comparison. And that peak torque comes in at an even lower RPM than the diesel, mind you...

Kubota's current D902 Diesel Engine, per their own website.
25hp @ 3,600 rpm
= 27.77hp per liter
41 ft/lb torque @ 2,600rpm
= 45.56 lb/ft per liter


Kubota's current WG972 gas engine, per their own website.
32.5hp @ 3,600rpm
= 33.43 hp per liter
50 ft/lbs torque @ 2,400 rpm.
= 51.44 lb/ft per liter


Kubota's current D902 Diesel Engine, per their own website. 25hp @ 3,600 rpm, 41 ft/lb torque @ 2,600rpm
sheetcatalog_d902-k_A4ill (kubotaengine.com)

Kubota's current WG972 gas engine, per their own website. 32.5hp @ 3,600rpm, and 50 ft/lbs torque @ 2,400 rpm.
WG972-G-E3(GAS)_front_ol_r_s (kubota.co.jp)

 

Yes the Ventrac offers a choice between these two water cooled engines (plus some air cooled gas). The general consensus is to go with the gas Kubota engine as it outperforms the diesel.

One thing to keep in mind is that nowadays diesel engines may be detuned to 25hp to avoid having emissions control garbage mandates.

So for example, in the Yanmar diesel engine line, the 1025/2025r JD tractors and the 994 ztr use the 1.27l 3 cylinder rated for 25hp. The 3025e also has a 25hp rating, but uses a 1.6l 3 cylinder engine. More torque to get the work done.

 

May I ask... What is the point of that ^^^ and what argument are you trying to make here?

 

Those aren’t the correct engines. I need the data on exactly the WG900 and the D900. Again, when I have the time to find the data, I will respond. I’m not all that interested in this debate because I know the answer and don’t feel the need to prove myself to make my point. I really couldn’t care if you understand it or not. But, when I find the time to get the data set of the two motors I mentioned I will. If I can even find it. They are the exact examples I need to make my case. There are others as well, but not applicable to the applications that we are discussing.

 

The more I mull the original question over, I'm thinking the answer to this question is, 30hp minimum for a $5,000 used machine.

Like many things in life however, I'm willing to compromise on my values for the right price though . Perhaps I'd be willing to "settle" for 27, if I could save a couple G's...

 

@Jashley73

Here's the best I can do because I can't find the data charts I want, so I'll use yours. Look at the torque curve that I highlighted in red on the power charts. See how the gas engine's torque curve rises as RPM decreases, but then flatlines? Whereas the diesel engine's torque curve rises steadily to a lower RPM rating? Now these two engines are kind of close, so we can use them and they are both engines used in various "lawn mowers". You can't say "all things equal" because there is no such thing. If you build two engines exactly the same, same displacement, same bore, same stroke, only one a gas and one a diesel, one of the two engines (likely the gas) will make a higher HP at the given RPM. That is because each fuel type takes a different build to accomplish the same thing. You can't build the two different fueled engines "the same" and get comparable results. Point I want to make is that as you load a diesel, the torque curve responds very differently to a gas engine. You can't say that a diesel has the potential to make more torque than a gas, because a gas also has the potential to make more than a diesel. The closest thing you can do is build a specific gas and a specific diesel to both make the same HP at the same RPM. We can agree that they will both make the same torque at that particular point in the chart. But as the engine is loaded, the diesels torque curve will change very different than the gas engine and assuming each engine was built as close to the same as possible (accounting in the build for their different fuel sources) the diesel will have a higher torque rise overall, while the gas engine will flatline. In the charts below, even though the diesel is a smaller engine, it's torque rises around 5 lbft overall. The gas only rises about 3 lbft. The diesel makes 2lbft more torque in rise than the gas does even though it is a smaller engine and lower HP. That's what I'm trying to get you to understand. A diesel's torque rise will always be better than a comparable gasoline engine. It's the nature of the fuel source. Also, the diesel will always burn less fuel.

I wanted to use the WG900 and the D900 to compare, but after I got to thinking, those weren't the right engines anyway. In the 80's, Cub Cadet offered a gas and diesel garden tractor. One had (I now realize) the WG640 and the other had the D640. They made 21hp and 17hp respectively even though they were the same bore, same stroke, same displacement. If you owned both tractors and used them with the same mower deck, you couldn't hardly tell a difference between the two machines, even though the diesel made less HP. It was because the torque rise of the diesel was greater at it's working range than the gas was. They had to go to a higher HP gas engine to get the same torque as the lower HP diesel motor. At the end of the day, the diesel would burn less fuel than the gas and they produced the same work about as equally as you can get. That's my point.

All things equal as they can be, a diesel will (I'm going to blanket statement this) ALWAYS have a greater torque rise than a comparable gas engine, do it at a lower HP and burn less fuel.

 

@Jashley73

Here's the best I can do because I can't find the data charts I want, so I'll use yours. Look at the torque curve that I highlighted in red on the power charts. See how the gas engine's torque curve rises as RPM decreases, but then flatlines?

View attachment 536102 View attachment 536103

When you say "Torque Curve," I'm assuming that you are referring to the shape of the "Torque" on the dyno graph, correct?

If so, great - we agree?

What you're telling me then, is that once you load the engine - meaning, you run into grass or leaves thick enough to begin bogging the engine down. The engine will now be at full throttle (meaning the gas engine's throttle plate is fully opened, and likewise the diesel's injection pump is now at max flow/throttle, etc...) If you do not slow down and decrease the load on the engine, it will continue to lose RPM until one of two things happens...

1- The engine falls in RPM to a point nearer it's max torque, which proves sufficient for the task at hand. The work is done (grass or leaves discharged) and then the engine recovers back to it's [max] operating speed, where the governor closes the throttle to maintain operating speed...

......or.....

2- The load is great enough that the engine RPM falls below the point of peak torque. At this point, the engine does not have sufficient torque/HP to overcome the load, and will stall/die if you don't reduce the load.




Agree?



If you look close at those graphs, right hand side, you can see that they adjust the scale up/down for shown torque values.

The gas engine - At no point does it's torque output FALL BELOW 65nm as shown on the graph.
The diesel engine - At no point does it's torque output EXCEED 57ish nm, and only at a very limited RPM window at that...

Let's put this a different way... At EVERY RPM on those dyno graphs, the diesel is 25-30% behind the gas engine in torque & HP output.




Let's go real world here - You're getting ready to cut an overgrown pasture. You grabbing the machine with 65+ nm of torque, or the one that barely cracks 57?

 

The ag industry may be different from the lawn industry, but the point is- that if gas could do the same type of heavy work as a diesel engine and last as well while using less fuel, there'd still be gas engine ag tractors. There aren't and the diesel engine is the only one being used in the ag industry as well as heavy mining etc where fossil fuels are concerned.

 

Jashley73-

My FX850 has a torque rating of just about 40 lb ft at 3600 rpms and rises to a peak of 45.6 lb ft at 2400 rpms/

The Yanmar diesel in my little CUT has a torque rating of 47.5 lb ft at its rated speed of 2650 rpms and a peak of 55.8 at 1600 rpms. The FX850 is rated at 27 HP and the Yanmar is 24 HP.

While I am not disputing any of your info about equal power at a certain rpm etc, the two different engines work completely different (as I'm sure you already know) and under adverse conditions, my diesel will simply out torque the more powerful gas engine in my ZTR.

I saw this firsthand vividly last fall mulching some very deep, and wet cottonwood leaves. They both did quite well and both had G5 blades under them, but the Z had an open chute and lugged down more than the diesel CUT which had the same sized deck, but was outfitted with a full mulch kit and was under much more load than the Z was under the same conditions. The diesel just lugged down to a certain point and kept on chugging along at a decent clip while I could almost stall the Z if I went as fast on the same stuff.

 

My FX850 has a torque rating of just about 40 lb ft at 3600 rpms and rises to a peak of 45.6 lb ft at 2400 rpms/

The Yanmar diesel in my little CUT has a torque rating of 47.5 lb ft at its rated speed of 2650 rpms and a peak of 55.8 at 1600 rpms. The FX850 is rated at 27 HP and the Yanmar is 24 HP.

There’s another data set that confirms higher torque rise with diesel. It is consistent data that is verifiable, comparing proper things.

 

Appreciate the invite, but too humid for me. LOL I do like Georgia though. It is quite nice in a lot of areas.

I lived in Orlando for several years and I hate the humidity. TN is bad enough for humidity, but at least it's a red state.