If it's true that you need so much PTO power that the HST would be overworked, I think you need to seriously consider going to a straight gear transmission (DT, in Kubota's model nomenclature), not a GST.
What many people don't realize is that there's more power loss between a DT and a GST than there is between a GST and an HST. Even most dealers make this mistake, because of the misconception that a GST is "just a DT with a hydraulic clutch", whereas the HST is a totally different kind of transmission, one which they generally don't understand. While the statement may be almost technically true, the inferences drawn from it are totally false. It's the hydraulic clutch pack that causes the loss. Here's why, primarily: The hydraulic clutch pack
engages by means of pressure. If it were to
disengage by means of pressure, the power loss would only occur when shifting gears, i.e. when the clutch was disengaged, but it would be difficult to get shifting to be as smooth and quick as it is in the current design. As it is, the power loss occurs when the clutch is engaged.
Anyone who doesn't believe this has got good company, because it's a very common misconception, but it's an misconception nonetheless. I posted the actual efficiency numbers I got from the Kubota service department once, but they're apparently in the old archive, which I can't seem to find anymore. I posted a message to Muhammad in another area asking him if they're still available anywhere.
Of course, while the above is all true, the case can still be made that HST incurs an incremental power loss when compared to the GST, which itself incurs power loss when compared to the DT, so there may be cases where the GST has barely enough power to do the job, therefore the HST has too little. In practice, in my opinion, if the HST
won't do it (for hours on end without damaging it), the GST
shouldn't be doing it.
Speaking of "in practice", though, my L4310HST will pull a 7' tiller with custom-added scarifier teeth through anything you can till with the the scarifiers fully extended and the tiller shaft buried 2" into the soil (so it's tilling over 10" deep). There's a picture of the tiller at
http://www.tractorbynet.com/cgi-bin/compact/showthreaded.pl?Cat=&Board=custom&Number=56678&page=0&view=collapsed&sb=5&vc=1#Post56678.
Or, put another way, as far as tractive force is concerned, consider this: My tractor has 19.5" wide Michelin XM27 radials on the back aired down to 9 psi with about 50 gallons of ballast in each tire, 11" wide Michelin radials on the front, a double-weight 4-in-1 bucket on the loader, an overhead console, a 2,000 pound Bradco backhoe on the back, and all kinds of extra weight in accessories (and a cup... /w3tcompact/icons/smile.gif). (You can also see pictures of the tires and other stuff at the above link.) Still, I can put the bucket against a tree and dig 4 holes in normal ground with the tires. What would I do with more power?
In all of this, we've only addressed one thing: power. I still contend that, given the safety, productivity, and ease-of-use advantages of HST, the vast majority of tractor purchasers would do well to think in terms of "How big an HST-equipped tractor do I need to buy to do the job?". You will be far happier, in the long run, than deciding to get a non-HST tractor in a particular size because it (possibly) has marginally enough more power than the HST to do the job.
Of course, I still haven't completely made up my mind as to which is better... /w3tcompact/icons/laugh.gif
MarkC
