===========================Although I understand your displacement/7cc argument, the 582 is rated for 64 HP. A 600R E-TEC is rated for 125 HP. Part of that is increased RPM, which goes to greater longevity if you're only running them at 6500 RPM, but part of that is much, much better combustion efficiency.
The principal big game changers for two-stroke engines have been direct injection, HVOF ceramic coatings and electronic ignition and injection control, which benefit from big improvements in computer power in the 30 years since the 582 was introduced.
The 600R and 850 E-TEC are purported by snowmobilers to have much better longevity than their predecessors and competitors. If you go out to buy a new Skidoo, they're upgrade options from the stock 4-strokes. (You can buy one off eBay used.)
Other improvements in the overall design over previous generations include the mono-block cylinders, an electronically-controlled three-position exhaust valve, more accurate balancing, integrated electric start, and much higher combustion efficiency. The 600R and 850 E-TEC actually run clean enough to pass California's emissions standards.
So yeah, if you plugged up the injectors and stuck new heads and a carburetor on a 600R, you could downgrade it to only a little better than what a 582 produces, but it would still be more reliable. I hope nobody would try to do that.
First you have to understand a 582UL is the same Core Engine as a Skidoo 580/582/583 which in a Sled is rated 97hp@7750rpm with a Tuned Pipe. Your 600 eTec is 116.7hp@8100rpm! You can see at 6500rpm it is 68.2hp@6500rpm!
Longevity on any Engine depends on WHO is Maintaining it, Flying or Riding behind it, and the Oil & Octane Gas they are using!
Avg Skidoo would fail around 3000 miles, Avg Trail Speed is 35mph, 3000/35 = 85.7 hrs. Rotax 582UL's have a 300hr TBO. E-Tec's Fail around 4000 miles. 4000/35 = 114.2 hrs! I got 6 Sleds, I bought all used. All have around 3200-3600 miles today.
(1) 1995 Yamaha Vmax 600 Never been touched.
(2) 1994 Yamaha Vmax 600 Had a New Base Gasket replaced recently. Replaced Pistons when I got it account guy had change the Jetting for the Mountains and never changed it back an burned a Hole in one Piston.
(3) 1998 Skidoo 670 never been touched!
(4) 1993 Arctic Cat 550 EXT, New Exhaust Gaskets.
(5) 1972 Skidoo 292 TNT my Vintage Racer.
(6) 1976 Arctic Cat Jag 2000 I got given to me for free, the guy had a Seizure.
I got probably 19 Skidoo Engines, some Singles and some Twins, and (1) JLO Single, most are complete Engines that all Run. A few need Carbs. Rotax Engines from the 70's, 80's and 90's. The JLO is the oldest at 2020-1970 = 50 years!
(3) 670's 1993+
(1) 617 Early 1990's Pro4
(2) 470's 1993+
(3) 503's 1993+
(3) 277's 1980's
(4) 335's 1971-1972
(1) 340 TNT 1971
(1) 247 1972
(1) 299 1970
(1) L-372 JLO 1970
I also probably got enough parts to assemble 3-5 more engines.
Do E-Tec's have better Emissions, Yes! I would really like to compare an e-Tec against a 582UL using either Hirth Blue Max or Amsoil Saber at 100:1. I, and most people don't really care about emissions! Hp and Reliability is what we care about. The 582UL is using a Muffler, not a Tuned Pipe like your e-Tec is. A 582UL with an R&D Aero Tuned Pipe. 80.7hp@6500rpm.
Do similar CC e-Tec's make more HP, Yes, account they use 594cc vs 580cc and a Higher 8000 vs 7750rpm and much Bigger Carbs/EFI than the Older Engines. That 582UL is using Bing 54 36mm Carbs, that 600 e-Tec is using a 54mm Throttle Bodies.
Unless Skidoo just started using Ceramics on their new Engines, they haven't in the Past. I have been preaching using Ceramics for many Years!
E-Tec's with EFI should get better fuel use, it doesn't really make you more hp. The Engine will Start better and run Smoother! You can add EFI to any older Engine, Ecotrons, Mega Squirt, has EFI Kit's. I have also promoted SFS EFI for Old Singles and Twins. Weber makes a nice DCOE EFI that can be adapted.
E-Tech Engines have been out for Years know, and Nobody that I know of has put one on a Plane. When that happens, it will be a Game Changer to see their Weakness!
Skidoo/Rotax has had a Crank Bearing issue for Years. They have tried going Bigger didn't really Help, they have went with a Sealed Bearing in the eTec, didn't work. There are some Hybrid Crank Bearings that use Steel Races with Ceramic Balls that I think will do the trick. But they Cost more than Standard Bearings. Need less Oil, Run Cooler, last 3x of Standard bearings they say.
600 eTec 68.2hp@6500rpm. I believe the 600HO is 125hp.