PSI is the MOR, Manufacture of Record, for the engines emissions system. It can only be the one of the manufacturers.
GM and Mazda have dropped their industrial engines and NACCO has gone to PSI for their alternative. The PSI 2.4 will be standard and the Kubota will be the Premium option. Sure looks like a Mitsi base.
The problem is trying to keep up with emission regulations.
MCFA used Nissan engines for some models.

From what I can tell from Googling images and configurations, cross checking with the limited information I've gotten from PSI and NACCO, I'm about 95% certain that it is based on the Mitsubishi 4G6#.

My Yale dealer still hasn't been able to provide me with any additional information. I'm about ready to pick up the phone and call PSI myself.

PSI is not an engine brand per se. They take the engine from the manufacturers and install the LPG fuel system. GM and the others don't want to be 'bothered' by the relatively small volumes of the forklift industry so they work through PSI aka PGL

They offer the PSI 2.4 or the Kubota 2.5

This is a very interesting discussion,
you can be sure there will be trucks with Mazda motors for the next 10 years or so... they won't suddenly go away.
you can also be sure that if the market doesn't think the new motor is worth keeping, they will come out with something different.
(and go figure, ?no multiple engine options for yale-hyster?)

Given that I have regularly put over 20000 hrs on my Mazda OHC industrial engines, I'd argue otherwise. I've got about 20 still in service that way. Two units with over 40K.

Sure, we get timing belts break, but those are easy fixes on the non-interference engine.

Only head issues I get are the occasional head gasket failure, and tar build-up on the valves. You can also run them out of oil and seize that cam.

That being said, the 16V head configuration on the new engine definitely has me a little concerned. Plus a balance shaft. No word on whether or not they are interference engines, but they show 4000 hr timing belt change interval.

Regardless of manufacturer, an overhead cam on an aluminum head is destined to be high maintenance with a relatively short lifespan compared to a conventional in block camshaft system.

That's currently my best guess as well. But that just comes from seeing visual similarities, and knowing there is a 16V SOHC Mitsu engine in those displacements. Nothing concrete.

I heard 4G64 Mitsubishi

I might be missing it, but the only reference I see to Kubota engines is the 2.5L optional engine on the 4000-7000 lb trucks.

I did just receive some addition information from Yale. Still nothing stating what the base engine is, but this might help:
4-cylinder single overhead cam design with 4 valves per cylinder
Cast iron engine block with a five main-bearing design for added strength
Aluminum cylinder head

I don't find anything matching this in Kubota's engine line-up.

Beeker,

The are Kubota engines. If you go to Hyster USA website you can click on the different models and it tells you which engine is used in which truck.

Here's a link to PSIs industrial engine line-up:
[url]http://www.psiengines.com/whatwedo/industrial-engines/[/url]

I'm trying to figure out what the 2.0L/2.4L engines are based off. I don't recognize them. Definitely not the GM/Vortec 4 cyl engine though.

Gonna miss those Mazdas. They've served me very well. I've probably put a million hrs on the ones in my fleet and had one single major failure... after it was run out of oil.

PSI had been doing the 3.0 and 4.3 GM engines for them for a while and GFI engine division, which is now owned by Impco, doing the 2.4 GM. So it does not surprise me that they would let PSI do the Kubota engines as well. Basically PSI dresses the engines to that OEM's spec. mostly the fuel system.
If memory serves me right it is who ever holds the EPA certification.

in the past, I have seen sticker for PSI, who was whom had made the emission systems, not complete motors.

The new engines will be from PSI. Trying to get more information myself, but it sounds like they're already in production with them.