# POLINI THOR 250

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#### Bille Floyd

##### Well-Known Member
==========================

Badlands doesn't show a 303 Price yet!

Polini Thor 303, 38hp at 8000 rpm!
(76mm x 62mm) 281.3cc at 6500rpm is probably 30-31hp Max!

$??????? ... POLINI THOR 303$4,100.00 – $5,275.00 Not sure why the web address says thor 250 ; but it does link to the 303 ? Bille #### Bille Floyd ##### Well-Known Member It's going to depend on the motor. Since there is no pitch control (trimmers and speedbar notwithstanding), "cruise" is whatever power setting gives you zero rate of climb. ... So Dana --- How do i calculate cruise for my Exxtacy glider ; with a 352Lb gross weight , sink rate = 147 ft/min, L/D = 17.5 : 1 ? Another question : That is 352-Lb gross, with the glider weight of 83-Lb , and it's suppose to be good for 8 G's ; can i add more gross weight and lower the G rating to say 6-g's ? Or it doesn't work that way ? Bille #### n3puppy ##### Well-Known Member Not sure why the web address says thor 250 ; but it does link to the 303 ? The Polini factory site no longer shows the 250 on the front page - just the 303 I wonder if factory sales of the 250 are on the way out in favor of the 303? "Stock on hand" at Distributors/dealers like Badland #### Dana ##### Super Moderator Staff member So Dana --- How do i calculate cruise for my Exxtacy glider ; with a 352Lb gross weight , sink rate = 147 ft/min, L/D = 17.5 : 1 ? Another question : That is 352-Lb gross, with the glider weight of 83-Lb , and it's suppose to be good for 8 G's ; can i add more gross weight and lower the G rating to say 6-g's ? Or it doesn't work that way ? Bille 147 rpm = 2.45 ft/s 2.45 * 352 = 862.4 lb-ft/sec = 1.57 THP (thrust horsepower) required for level flight at the same airspeed you measured the sink at. Divide THP by propeller efficiency to get shaft (engine) HP. Alternately, knowing the 17.5:1 L/D, you have 352/17.5 or 20.1# drag, meaning you need an equal amount of thrust to maintain altitude. Thrust * airspeed equals THP. You didn't give the airspeed, 862.4 / 20.1 = 42.9 ft/s or 29.3 mph, is that your glide speed? Of course the above is simplified; in the real world, depending on the aircraft and powerplant design trim changes and other effects of adding power will make it less efficient above and beyond prop efficiency, which may already be as low as 60%. #### EzyBuildWing ##### Well-Known Member To increase 2-Stroke longevity, reduce mechanical and thermal stress. Maybe lower compression-ratio by installing an extra head-gasket, and run at lower RPM and live with the lower hp output. Armilite's suggestions earlier sound excellent. Perhaps Armilite might comment on how to make a 582 last for ever, and what would be ideal max hp and cruise hp? (eg: install efi, lower CR, install rpm-limiter, install fuel-flow limiter, Evans coolant, daily-fresh gasoline, filter-funnel etc)? This is great Forum #### n3puppy ##### Well-Known Member Let me start out by saying I am not in favor of 8000rpm engine speeds BUT - What are the down sides? Wear is one - but how much worse? Pistons and rings wear because of friction against the cylinder wall. Higher RPM - more up and down, more wear. But engines have different stroke lengths - the 'Wear Distance" is longer on long stroke engines. Example -Thor 250 in question has a 60mm stroke. At 8000 rpm, the piston scapes 3150 ft of cylinder wall per minute. - That' a lot. But the Simoni Victor series has 76mm stroke. At only 6200rpm wear is right up there at 3092 ft/min of scraping Just 2% less. Even the Hirth F33 single (69mm) and Rotax Rick's 670 (70mm) are bumping the 3000 ft/min mark if run at 6500 rpm. Thoughts? #### Bille Floyd ##### Well-Known Member I wish, (No, Really wish) someone made a 30 hp twin , with E-start and EFI ; that weighed Under 40-Lb , (with exhaust, and reduction) !! Twins vibrate Less (.) I know it can be done ; look at the 3W-342 , and add the other stuff i want : The Hirth F-23 comes close ; but i don't need 50 hp, and it needs to loose 10-Lb. Bille Last edited: #### EzyBuildWing ##### Well-Known Member Cuyuna 430D was produced in 1981. 2-cyl, 430cc, aircooled, 64 lbs, 30 hp at 5,500 rpm. In a snowmobile, it gave 40hp with good reliability. But for GREAT reliability it was detuned to 30 hp by adding an extra head-gasket. So 430/30 = 14cc per hp for great reliability, so says Cuyuna. Polini 280 cc = 20 hp at 14cc/hp. #### n3puppy ##### Well-Known Member Cuyuna 430D was produced in 1981. 2-cyl, 430cc, aircooled, 64 lbs, 30 hp at 5,500 rpm. In a snowmobile, it gave 40hp with good reliability. But for GREAT reliability it was detuned to 30 hp by adding an extra head-gasket. So 430/30 = 14cc per hp for great reliability, so says Cuyuna. Polini 280 cc = 20 hp at 14cc/hp. Loved that version of the engine. Pterodactyl / Quicksilver drivers at our airpark had few problems. Felt bad when Quicksilver started using the 35hp Rotax 377. Started a HP war. When Cuyuna bumped up the Hp to compete, never felt quite the same reliability wise. #### Armilite ##### Well-Known Member POLINI THOR 303$4,100.00 – $5,275.00 Not sure why the web address says thor 250 ; but it does link to the 303 ? Bille ======================== Why anyone would Pay that kind of money for only 36hp/[email protected] that only lasts 250-300hrs even using 100LL, is beyond me. A Rotax B Gear Drive New is$835. New A Drives are also still around also. I have seen New Kawasaki 440's on eBay going for $950. You can buy a good used Rotax 277UL for$250 to $500 with a Gear Drive, or source the main parts used like Head ($50), Cylinder ($125), Case ($125), Crank ($125), and build a Custom Engine with all the Bells & Whistles, Porting, Engine Coatings, a Tuned Pipe and still be 1/4th the Price of a Polini. Stock 277UL 268.4cc/7cc = [email protected] You can also Big Bore it for more CC = more hp! If you called all the Skidoo Dealers in your area and Ultralight Dealers, they might have some of these NOS Parts or Motors sitting on a Shelf. I have been given a NEW 277UL and a New 447UL Case given to me for favors that I did for a guy who had bought out another Dealer. I even once got a low 75 Hour 582UL Case that had Ethanol run thru a Fiberglass Gas Tank and gummed up the Engine. 15 min in my Glass Bead Cabinet and it cleaned up like New. Arctic Cat has a New 397cc Single 65hp EFI that may make a nice Ultralight/Kitplane Engine. I haven't seen the PTO Side yet, but if they made a ReDrive for the Polini, this Engine is from the same family only Bigger Bore & Stroke. #### Attachments • 38.6 KB Views: 5 #### cluttonfred ##### Well-Known Member HBA Supporter You weren't really asking a question, but I'll respond anyway. I think many potential aircraft homebuilders (including me) don't have experience tearing down and building up engines, two-stroke or otherwise. They may be reasonably handy in a DIY projects and follow-the-instructions kind of way, but that's it. They would rather buy something off the shelf rather than risk doing something stupid that could compromise an aircraft engine. In my case, it's not that I don't think I could learn to tear down and rebuild an engine, that's just not where I want to invest my time at this point in my life. I would tackle building up a VW engine from a kit or a conversion manual because I would have step by step instructions and available support. I feel the same way bout installing a proven engine package like the Polini Thor 250DS. That's one reason why I think there is a market for an industrial V-twin parts kit (redrive, lightened flywheel, exhaust, etc.) if someone were to put the time and effort in to develop a good, step by step manual and provide builder support. Not just "here's a web page about how I did it myself," but a real package that either includes the base engine or tells you exactly what make(s) and model(s) of base engine you should go get. Why anyone would Pay that kind of money for only 36hp/[email protected] that only lasts 250-300hrs even using 100LL, is beyond me. #### Bille Floyd ##### Well-Known Member ======================== Why anyone would Pay that kind of money for only 36hp/[email protected] that only lasts 250-300hrs even using 100LL, is beyond me. ... You have a Very Good point here !! I would pay$3,100 for the 33hp , 202 ; knowing full well it won't
last for squat , (mostly because of the light weight) and it's about
average for what a PPG engine goes for nowadays.

What I would like to see a Chinese made , (Valach Motors VM R5-420)
with a slightly longer stroke to turn lower rpm ; make it in the low
$3k range please !! Speaking about the thor 202 : I only need 25-27-hp ; would the double head gasket trick work on that 33-hp engine ? Bille #### n3puppy ##### Well-Known Member ======================== Arctic Cat has a New 397cc Single 65hp EFI that may make a nice Ultralight/Kitplane Engine. I haven't seen the PTO Side yet, but if they made a ReDrive for the Polini, this Engine is from the same family only Bigger Bore & Stroke. The Blast 4000 engine is in-house designed and built by Arctic- no Italian connection that I have heard. Uses same cylinder and other parts as their 800cc [email protected] twin. 800 twin and 400 single both use side frame mounting so have PTO area mounting holes that might be used for re-drive. However using those mounting points for re-drive may complicate airframe mounting. Long block price is$1500. Probably most of the mechanical but not electric CDI, computer, sensors etc etc etc. The ECM alone is $2000+ and the fly wheel, stator, triggers$1300+
All up with Belt drive etc its going to be well into the \$6000+ range

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#### n3puppy

##### Well-Known Member
Speaking about the thor 202 :
I only need 25-27-hp ; would the double head gasket trick work
on that 33-hp engine ?
We did it back in the day with the Cuyuna's but they were not hi-performance to begin with.

As the snowmobile companies (Scorpion etc) pushed them harder, the squish clearance became critical. One head gasket but multiple thickness base gaskets (5,3,1,.75mm) Mix and match to get squish correct by lifting or lowering the whole cylinder.

Besides squish on the hi performance Thor 202 you have the water cooling issue. It was not uncommon to find a little exhaust weep past the double gaskets on the old Cuyunas.
Not pretty, but not destructive either.

On a water-cooled engine - exhaust in the water jacket, or worse, water into the cylinder is going to be bad

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