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Posted by Jack on May 15, 2007, 7:06 am
I've always used 16-18 hp units with 48-50" mower decks.
Unfortunately, new units in that hp. range come with 42" decks. To
get a larger deck, I need to get units 23-27 hp.
Does a unit in 23-27 hp. range use appreciably more gas than a 18 hp.
unit, assuming same driving speed and workload? Thx.
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Posted by dpb on May 15, 2007, 9:00 am
On May 15, 6:06 am, Windswept@home (Jack) wrote:
> I've always used 16-18 hp units with 48-50" mower decks.
> Unfortunately, new units in that hp. range come with 42" decks. To
> get a larger deck, I need to get units 23-27 hp.
> Does a unit in 23-27 hp. range use appreciably more gas than a 18 hp.
> unit, assuming same driving speed and workload? Thx.
Even if you could arrange for the actual engine load to be the same
(which it may approximate), the larger displacement/horsepower engine
is still likely to use more fuel simply from the size difference.
But, in general, if you can effectively use such a large deck, the
actual _total_ fuel used can probably be kept to nearly the same by
running at a higher ground speed so the extra power can be utilized to
cover the same ground in less time negating the higher per hour fuel
consumption. If, otoh, you have to run at a low speed to avoid
obstacles or make many turns, back up, etc., and the time required is
the same you'll undoubtedly find the fuel consumption noticeably
higher.
The only consolation may be that the newer, larger engines may be
slightly more efficient. If you're going that large though, I'd
suggest at least consideration of diesel.
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Posted by trainfan1 on May 15, 2007, 3:04 pm
dpb wrote:
> On May 15, 6:06 am, Windswept@home (Jack) wrote:
>> I've always used 16-18 hp units with 48-50" mower decks.
>> Unfortunately, new units in that hp. range come with 42" decks. To
>> get a larger deck, I need to get units 23-27 hp.
>> Does a unit in 23-27 hp. range use appreciably more gas than a 18 hp.
>> unit, assuming same driving speed and workload? Thx.
>
> Even if you could arrange for the actual engine load to be the same
> (which it may approximate), the larger displacement/horsepower engine
> is still likely to use more fuel simply from the size difference.
> But, in general, if you can effectively use such a large deck, the
> actual _total_ fuel used can probably be kept to nearly the same by
> running at a higher ground speed so the extra power can be utilized to
> cover the same ground in less time negating the higher per hour fuel
> consumption. If, otoh, you have to run at a low speed to avoid
> obstacles or make many turns, back up, etc., and the time required is
> the same you'll undoubtedly find the fuel consumption noticeably
> higher.
>
> The only consolation may be that the newer, larger engines may be
> slightly more efficient. If you're going that large though, I'd
> suggest at least consideration of diesel.
>
It's about the same amount of work, and should be pretty close. The
blades use much more fuel than propulsion, especially in non-hydrostatic
mowers, so with a larger deck there is a lot less maneuvering to hit the
next row(many fewer rows).
Rob
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Posted by dpb on May 15, 2007, 3:54 pm
> dpb wrote:
> > On May 15, 6:06 am, Windswept@home (Jack) wrote:
> >> I've always used 16-18 hp units with 48-50" mower decks.
> >> Unfortunately, new units in that hp. range come with 42" decks. To
> >> get a larger deck, I need to get units 23-27 hp.
> >> Does a unit in 23-27 hp. range use appreciably more gas than a 18 hp.
> >> unit, assuming same driving speed and workload? Thx.
> > Even if you could arrange for the actual engine load to be the same
> > (which it may approximate), the larger displacement/horsepower engine
> > is still likely to use more fuel simply from the size difference.
> > But, in general, if you can effectively use such a large deck, the
> > actual _total_ fuel used can probably be kept to nearly the same by
> > running at a higher ground speed so the extra power can be utilized to
> > cover the same ground in less time negating the higher per hour fuel
> > consumption. If, otoh, you have to run at a low speed to avoid
> > obstacles or make many turns, back up, etc., and the time required is
> > the same you'll undoubtedly find the fuel consumption noticeably
> > higher.
> > The only consolation may be that the newer, larger engines may be
> > slightly more efficient. If you're going that large though, I'd
> > suggest at least consideration of diesel.
> It's about the same amount of work, and should be pretty close. The
> blades use much more fuel than propulsion, especially in non-hydrostatic
> mowers, so with a larger deck there is a lot less maneuvering to hit the
> next row(many fewer rows).
What's about the same amount of work as what else? No clue what
you're driving at unless you're thinking because two decks are the
same size the cutting work is the same therefore the fuel consumption
should be similar. There's a little truth in that, but it's also true
that the engine needs to run at a fixed rpm to generate the blade tip
speed and to do that will mean the larger engine will consume more
fuel. Similar as to the relative fuel economy of a V8 vis a vis a V6
both running down the road at 65 mph--both needing about the same hp
to keep then going, but the one is less fuel-efficient than the
other. Larger engine-->larger carb jets-->higher fuel consumption.
Didn't look to see, but manufacturers of commercial machines should
provide fuel consumption numbers.
I don't know exact percentages, but I'd venture that a significant
percentage of current mowers of 20+ hp and 48" or larger decks will
have the hydrostatic transmission which is one prime reason they have
the larger engines. That is, as I say, not a heavily researched fact
but a hypothesis based on what have observed of machines I've recently
looked at...
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Posted by trainfan1 on May 15, 2007, 4:30 pm
dpb wrote:
>> dpb wrote:
>>> On May 15, 6:06 am, Windswept@home (Jack) wrote:
>>>> I've always used 16-18 hp units with 48-50" mower decks.
>>>> Unfortunately, new units in that hp. range come with 42" decks. To
>>>> get a larger deck, I need to get units 23-27 hp.
>>>> Does a unit in 23-27 hp. range use appreciably more gas than a 18 hp.
>>>> unit, assuming same driving speed and workload? Thx.
>>> Even if you could arrange for the actual engine load to be the same
>>> (which it may approximate), the larger displacement/horsepower engine
>>> is still likely to use more fuel simply from the size difference.
>>> But, in general, if you can effectively use such a large deck, the
>>> actual _total_ fuel used can probably be kept to nearly the same by
>>> running at a higher ground speed so the extra power can be utilized to
>>> cover the same ground in less time negating the higher per hour fuel
>>> consumption. If, otoh, you have to run at a low speed to avoid
>>> obstacles or make many turns, back up, etc., and the time required is
>>> the same you'll undoubtedly find the fuel consumption noticeably
>>> higher.
>>> The only consolation may be that the newer, larger engines may be
>>> slightly more efficient. If you're going that large though, I'd
>>> suggest at least consideration of diesel.
>> It's about the same amount of work, and should be pretty close. The
>> blades use much more fuel than propulsion, especially in non-hydrostatic
>> mowers, so with a larger deck there is a lot less maneuvering to hit the
>> next row(many fewer rows).
>
> What's about the same amount of work as what else?
The lawn has to be entirely cut.
Each machine has to do the same amount of work for the same lawn.
The larger deck, though, will do it in fewer passes. This would likely
be offset by the overhead of a slightly larger engine.
I use less gas with a 18hp lawn tractor than with a 5.5hp self-propelled
mower for the same piece of lawn. It takes a lot less time too.
Don't forget the value of your time when considering a larger mower.
You always come out ahead, even if you use more fuel.
Rob
> No clue what
> you're driving at unless you're thinking because two decks are the
> same size the cutting work is the same therefore the fuel consumption
> should be similar. There's a little truth in that, but it's also true
> that the engine needs to run at a fixed rpm to generate the blade tip
> speed and to do that will mean the larger engine will consume more
> fuel. Similar as to the relative fuel economy of a V8 vis a vis a V6
> both running down the road at 65 mph--both needing about the same hp
> to keep then going, but the one is less fuel-efficient than the
> other. Larger engine-->larger carb jets-->higher fuel consumption.
> Didn't look to see, but manufacturers of commercial machines should
> provide fuel consumption numbers.
>
> I don't know exact percentages, but I'd venture that a significant
> percentage of current mowers of 20+ hp and 48" or larger decks will
> have the hydrostatic transmission which is one prime reason they have
> the larger engines. That is, as I say, not a heavily researched fact
> but a hypothesis based on what have observed of machines I've recently
> looked at...
>
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> Unfortunately, new units in that hp. range come with 42" decks. To
> get a larger deck, I need to get units 23-27 hp.
> Does a unit in 23-27 hp. range use appreciably more gas than a 18 hp.
> unit, assuming same driving speed and workload? Thx.