Any news on gas engine CUTS?

[AxleHub]

Who uses a CUT or SCUT at max rated rpm and at full rated power for hours at a time. If you do , you purchased a hobby tractor that is two or three sizes too small. The typical small tractor is a 50 to 100hr a year machine performing puttering around jobs. If somebody has set out with a 2x14 plough into a 100 acre field . The operator is overly optimistic .

Anyone who is cutting 12 to 20 inch grass.

Anyone who is tilling community gardens

Anyone who is snowblowing in WI, MN, or MI snowfalls on wind driven ridges .

Anyone who thinks $15,000 to $35,000 is real money.

 

[SPYDERLK]

Who uses a CUT or SCUT at max rated rpm and at full rated power for hours at a time. If you do , you purchased a hobby tractor that is two or three sizes too small. The typical small tractor is a 50 to 100hr a year machine performing puttering around jobs. If somebody has set out with a 2x14 plough into a 100 acre field . The operator is overly optimistic .

Typical hrs/yr do not equate to typical proportion of full load used when its running. HST is easy to run at full load if you have a motion based load.

 

[SPYDERLK]

Sounds fine. But that was only for 1/2 hour. Scut and cut tractors need to run for hour after hour after hour.

Just as importantly . . your radiator didn't overheat but what was youe engine temperature? Wide open . . . Wow . . . Good way to cook your oil or tranny fluid.

Exhaust valves too and maybe rings.

 

[aczlan]

Anyone who is cutting 12 to 20 inch grass.

Or lush 5-8" tall irrigated grass. I have mowed both "hayfield" grass/weeds that is 12-36" tall and 5-8" tall irrigated grass and the shorter thicker grass put a lot more load on the engine.
I would hazard a guess that most commercial zero turns spend a much greater percent of their running time at or near rated power than most CUTs and SCUTs during mowing season.
Yes, mowing tall grass will make a CUT or SCUT work, but our BX2660 (with the 60" deck) cannot go fast enough to bog down and get to 100% load unless its an area that hasn't been mowed for 3-4 weeks.

Aaron Z

 

[AxleHub]

Or lush 5-8" tall irrigated grass. I have mowed both "hayfield" grass/weeds that is 12-36" tall and 5-8" tall irrigated grass and the shorter thicker grass put a lot more load on the engine.
I would hazard a guess that most commercial zero turns spend a much greater percent of their running time at or near rated power than most CUTs and SCUTs during mowing season.
Yes, mowing tall grass will make a CUT or SCUT work, but our BX2660 (with the 60" deck) cannot go fast enough to bog down and get to 100% load unless its an area that hasn't been mowed for 3-4 weeks.

Aaron Z

Obviously your experience is with sparse grass. I cut 5 to 8 inch bluegrass all the time and it is thick and lush and that cettainly doesn't challenge my engine like the tall wetlands grasses do. There is no way my zero turn could cut that area without frequent cool down breaks and a need for triple cutting.

 

[aczlan]

What ZTR do you have? My ZTR experience is mostly with 2005ish 25-27HP (Kawasaki) air or water cooled Exmark Lazer Z mowers with 60" and 72" decks on them mowing a mox of fields, non-irrigated "normal" grass and irrigated lush thick grass. We were not allowed to have any appreciable amount of visible clippings, so the lush grass got double or triple cut in the spring/early summer.
As long as we kept the radiators/cooling fins blown out they never even thought about overheating (no matter how hard the guys pushed them). Bog down, yes. Stall out, yes. Burn up the "mule belt" that went from the engine to the desk jackshaft, yes (on occasion). Kill the engine when the nylon gear driving the oil pump stripped, but not overheat.

Aaron Z

 

[kenmac]

What ZTR do you have? My ZTR experience is mostly with 2005ish 25-27HP (Kawasaki) air or water cooled Exmark Lazer Z mowers with 60" and 72" decks on them mowing a mox of fields, non-irrigated "normal" grass and irrigated lush thick grass. We were not allowed to have any appreciable amount of visible clippings, so the lush grass got double or triple cut in the spring/early summer.
As long as we kept the radiators/cooling fins blown out they never even thought about overheating (no matter how hard the guys pushed them). Bog down, yes. Stall out, yes. Burn up the "mule belt" that went from the engine to the desk jackshaft, yes (on occasion). Kill the engine when the nylon gear driving the oil pump stripped, but not overheat.

Aaron Z

I'm with you.. I have a z turn 22 hp Kawasaki .. I cut about 5 acres of grass..
Run the engine wide open for hrs..Wide open is the way they are designed to run..
Never burn up the oil or run hot.. Mine is an air cooled engine

I have heard of this super duper tough grass ,that some have.. I understand no gasoline engine can stand the stress of cutting it

 

[paulfun9]

One of the gaping holes that "gas engines for scuts and cuts" keeping talking about without reference . . Is what is needed in a gas engine to mimic the performance of diesel in a scut or cut tractor.

It will require high compression gas engines with clean burn characteristics. A high compression engine is typically defined as an above 9.1 compression ratio. 9.1 and below allows use of regular gas (preferably none ethanol). To attain both cleaner burning and higher compression ratio performance a non-ethanol octane of 90 or above is desired with even higher octane levels for cpmpression ratios above 12.

Failure to use a higher octane in a high compression engine will cause 2 things:

1. Decreased actual burning of the gas fuel = lower mileage/hours per gallon.

2. Increased unburned hydrocarbons and emission issues.

That means premium gas and premium gas pricing . . Current price in our area is $3.29.

My massey gc1715 duesel operates at a 22.5 compression ratio and I use premium diesel (including road tax) of $ 2.59 per gallon.

Now isn't it strange that gas proponents don't seem to mention this that the fuel costs of a yet to be developed gas scut/cut tractor engine would actually be considerably higher than diesel . . . not lower

Your way off on your calculations! There wont be a need for premium fuel and there wont be a need for a compression ratio at 12 to 1. You are not taking into account dynamic compression and the duration and overlap of the cam you will need to get the power rating needed for a tractor use.

 

[paulfun9]

My 11:5 compression ratio motorcycle runs on 87, and was designed to use it. Looks like there's more involved in engine designing than you understand.

There is more involved than most here will ever understand! I also have a few engines with compression ratios higher than 11;5 that run on 87.

 

[sd455dan]

No one has mentioned compression ratios. If you tried to put 23/1 compression on a gasoline engine, it would be disasterous.

Eugene

Direct injection solves much of this- can't have preignition if the fuel isn't injected until after the point of pistons relationship to tdc that preignition can occur.


Or there might also be a change in the size and strength of the parts -starting with pistons/ rods

my 554 diesel tractors piston/rod vs. my boats Volvo OHC gas piston/rod compare this way...


Both will run at rated power for a very long time- one at @ 5000rpm @ 9:1 130 hp 130 cu inch

the other @ 2000rpm @16:1 and (only) 55 hp 203 cu inch guess which one is the 55 hp diesel :laughing:



I like the HD low rpm diesel design for tractor work. the gas version works well for a boat engine that needs a much wider RPM operating range

I would think that a gas engine would actually work pretty well for a hydrostatic drive tractor- ( pin the throttle) and go

but if a gear drive- give me a low rpm/large cu inch diesel all the way