[Mowingman]

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

Yes I do remember that. My first 60" ZTR only had 22HP. It worked fine, but struggled some in overgrown or very thick grasses. Later, I owned a 23HP machine, then several that were 25HP and up. today, with gas costs being what they are, I would go with the least HP that will do the job I need to do.

 

[rippinryno]

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.

 

[kinneberg lawn service]

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.

 

[Jashley73]

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.

 

[Jashley73]

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...

 

[J. Baker]

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.

 

[Ridin' Green]

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

 

[Brucey]

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.

Unfortunately that new proposed law says at or below 25hp.

[325F.187] FOSSIL FUEL POWERED LAWN AND GARDEN EQUIPMENT; PROHIBITION.

(a) On and after January 1, 2025, new lawn and garden equipment sold, offered for sale, or distributed in or into Minnesota must be powered solely by electricity.

(b) For the purposes of this section, the following terms have the meanings given:

(1) "lawn and garden equipment" means any of the following types of equipment
powered by a spark ignition engine rated at or below 19 kilowatts or 25 gross
horsepower:

(i) lawnmower;

(ii) leaf blower;

(iii) hedge clipper;

(iv) chainsaw;

(v) lawn edger;

(vi) string trimmer; or

(vii) brushcutter; and

 

[Brucey]

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...

Diesel engine has a few advantages for torque production.

1. Higher compression ratio.
2. Speed of combustion.
3. Bore/stroke - generally a diesel will have a longer stroke.
4. Diesel is more energy dense than gas.

 

[Jashley73]

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.

I mist be a glutton for punishment. Please enlighten us...

 

[Jashley73]

Diesel engine has a few advantages for torque production.

1. Higher compression ratio.
2. Speed of combustion.
3. Bore/stroke - generally a diesel will have a longer stroke.
4. Diesel is more energy dense than gas.

You are correct in the design attributes. But again, those are all just attributes. Power output is power output.

I'm anxiously awaiting JBaker's masterclass on how Tq. x RPM is incorrect in calculating engine horsepower.

 

[Chilehead]

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

The Scag STHM!! How could I forget? Back in the 90s I worked for another landscaping company that used these mowers. Man, I miss those. They could hold a slope darn near as good as a walk-behind. You're right about the tranny. I recall it used a transaxle. The guy I worked for had an old Bobcat 3-wheeler, too (when Textron was making them). Ferris is the only one left that makes this style of mower--and yes, they used less power than modern Zs.

 

[rippinryno]

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

 

[Brucey]

You are correct in the design attributes. But again, those are all just attributes. Power output is power output.

I'm anxiously awaiting JBaker's masterclass on how Tq. x RPM is incorrect in calculating engine horsepower.

I don't see his posts but given a diesel is unlikely to ever be revving at 5252rpm, I'm not sure it matters. A diesel makes more torque at lower rpm by virtue of longer stroke and higher cylinder pressure. It has to be built much stronger to deal with that. This adds weight and cost. A gas engine has a shorter stroke and less pressure and can rev higher. Cheaper to build and lighter. Saying that a gas and diesel engine are going to have the same torque at 3600rpm just doesn't make sense.

 

[Jashley73]

I don't see his posts but given a diesel is unlikely to ever be revving at 5252rpm, I'm not sure it matters. A diesel makes more torque at lower rpm by virtue of longer stroke and higher cylinder pressure. It has to be built much stronger to deal with that. This adds weight and cost. A gas engine has a shorter stroke and less pressure and can rev higher. Cheaper to build and lighter. Saying that a gas and diesel engine are going to have the same torque at 3600rpm just doesn't make sense.

A diesel engine has potential to make more torque at lower RPM because of those attributes, however it's no gurantee. (Though you are correct, practically, they often do make more torque, all things being equal, if there ever was such a thing.)


What I said was, they would have the same torque at 3,600 rpm, if they were rated the same HP at 3,600rpm. This much is just simple mathematics.

They may produce different torque from each other at different RPM's.

We're talking small engines for mowers, where the operating speed is usually 3,600rpm, and this is where the engine's published power is usually rated. 25hp at 3,600rpm is still 25hp. Regardless of what type of fuel or energy is used to create it.

 

[J. Baker]

I mist be a glutton for punishment. Please enlighten us...

You didn’t understand the lesson last time. You won’t this time. You don’t understand torque rise. Better keep reading on the internet. You’ll believe anything as long as I’m not the one it’s coming from.

 

[Brucey]

A diesel engine has potential to make more torque at lower RPM because of those attributes, however it's no gurantee. (Though you are correct, practically, they often do make more torque, all things being equal, if there ever was such a thing.)


What I said was, they would have the same torque at 3,600 rpm, if they were rated the same HP at 3,600rpm. This much is just simple mathematics.

They may produce different torque from each other at different RPM's.

We're talking small engines for mowers, where the operating speed is usually 3,600rpm, and this is where the engine's published power is usually rated. 25hp at 3,600rpm is still 25hp. Regardless of what type of fuel or energy is used to create it.

Right but small diesels on mowers are generally running below 3600 rpm. My 25hp Yanmar on the 994 is at 3200rpm and the 37hp on the 997r is at 3000 rpm.

To me when selecting an engine, one needs to look at the torque curve, and not just the simple HP rating. When you get into thick/heavy/wet growth, the rpms are going to drop from the normal rpm (say 3600rpm in a gas unit). This is where a diesel engine usually has an advantage because they make more torque down lower in the rpm range.

Is torque more important than horsepower?

People talk about torque and horsepower all the time, and both numbers will be debated to death on car forums. But what exactly do they mean, and which one matters more?

www.carthrottle.com

 

[Jashley73]

You didn’t understand the lesson last time. You won’t this time. You don’t understand torque rise. Better keep reading on the internet. You’ll believe anything as long as I’m not the one it’s coming from.

J, I went back a scanned this thread start to finish.

I didn't see any lessons from you on this topic, in this thread. Maybe your memory too is sharper than mine, and you've schooled me on this in the past. If so, please point me in that direction.



I learned a long time ago to swallow my pride. I have no such pride invested in this argument, nor any other if I'm being honest. I don't like remaining ignorant, so if you have superior knowledge, please do share it - in a manner that's not condescending perhaps - so that we can all learn.

If you're not going to offer anything constructive, and are just going to call myself & others stupid liars - which I've noticed seems to be a trend with you - then please just refrain from the conversation.

With that out of the way, if you have some other knowledge that you wouldn't mind sharing, then please do. It doesn't bother me one bit to admit that I was wrong. And if so, I'll gladly go back & delete the erroneous posts of mine, without any hurt feelings.

 

[rippinryno]

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.

 

[Jashley73]

Right but small diesels on mowers are generally running below 3600 rpm. My 25hp Yanmar on the 994 is at 3200rpm and the 37hp on the 997r is at 3000 rpm.

To me when selecting an engine, one needs to look at the torque curve, and not just the simple HP rating. When you get into thick/heavy/wet growth, the rpms are going to drop from the normal rpm (say 3600rpm in a gas unit). This is where a diesel engine usually has an advantage because they make more torque down lower in the rpm range.

I certainly wouldn't argue that your diesel engines make more peak torque below their max operating RPM. However, so can gas engines. And within the context of our small engines on mowers, most produce their peak torque below their max operating RPM, just as you described of your diesel engines. (And I have no reason to doubt your stated numbers, nor your experience either.)

Just a sample dyno graph of a 38.5hp Kawasaki FX1000 EFI which clearly shows that same characteristic as well.