850 Engine thread (840cc)

mountainhorse · Mar 7, 2018

Its always possible to make more power.

BUT...

Maybe, Just maybe they found the right balance between power and character....Torque and nimbleness.

We'll see in about 9 months.

RMK935VA · Mar 7, 2018

I wonder if the purposely unbalanced clutch on the Ski Doo 850 is the source of their reported belt problems. As I understand it, the primary acts as a counterbalanced for the motor. Anyway, I like the Polaris dimensions and reported lack of vibration. Maybe they have found the sweet spot.

AndrettiDog · Mar 8, 2018

Matte Murder said:
I wonder why Polaris didn’t step over Doo and build a 900. Is there something about the 800cc ish engine size that limits going much bigger? So the aftermarket is going to do “bigger bores” lol on the Poo 850 just like Trygstad did with the 850/927. Wonder why Polaris didn’t spit in Ski Doos corporate face with a 900/950 and put them in the back seat engine wise for a couple seasons.

I think for the same reason mountainhorse stated. The sled just would act different (possibly bigger and more luggy) if they went to 900cc's. I also think that all manufacturer's push the bounds of reliability naturally in this sport, but the 900's and 1000's two strokes were never known to be reliable. Regardless if it was Polaris, AC or Doo. I rode the AC and Doo 1000's back in the day a little and it was like having a diesel motor. Tons of torque and not the same snap as an 800.

mountainhorse · Mar 8, 2018

Bigger displacements:
To make a big oversquare engine like a true 900cc with a 74mm stroke... you are running 88mm pistons.
You need to have a good piston skirt length to bore ratio... which then stretches out the height of the cylinder, rod length and add rotational mass which would need to be compensated for with larger bob weights of the crank.

I guarantee that engineers in Roseau learned from the 866cc '900's of the past, with the big 80mm-stroke... and what does and does not work, from experience and the school of hard knocks... so they are most likely 'not missing the boat' for optimal powerplant dimensions for MOST of the mountain riders out there.

Lots to consider:
You still need to fit the engine in the sled, keep it compact, make it so that it works in synergy with the nimbleness of the chassis, has snappy throttle response with moderate compression on pump gas, and vibrates as little as possible, has a reasonable cost and can be mass produced with good QC...AND, will function well/durably in GREATLY varying altitudes/air-density/temps/abuse/fuel....Emissions considerations ta boot!.... All while giving the beancounters the confidence of putting a 4yr warranty on the sled.

I'm not sure if you all know just how difficult that is to pull off... a sled that will run strong from sea-level to 13,000 feet with only small clutch calibration changes... HMM.

Quite a feat.

I really hope that Polaris integrates all of these changes in the 840cc into a super potent 600cc package in the near future.

.

mountainhorse · Mar 8, 2018

I believe that one of the things that is making these new evolutions of the CFi engines better each year.... the control system is getting that much better.

It would be nice to have closed-loop fuel system... but not practical on a mass produced two-stroke... So we have things like pipe temp, coolant temp, air temp, MAP, TPS, DET and now fuel pressure monitoring and on-the-fly automatic adjustment based on these variables... hundreds of times per second...brings the reliability up greatly.

My biggest hope for 2019 is that the engineers in Roseau were able to work with the accountants in Medina well enough to invest in a marked improvement in the quality and componentry of the electrical system on these beasts.... It really is needed to evolve this product.

.

89sandman · Mar 8, 2018

It always amazes me how far behind in electronic technology powersports are. Using 40 year old systems to run your engine today just seems silly. Not having a universal scan port and cheap scanners to read codes is even more dumb than the technology they use. I guess we should just be thankful we're still not using carbs

mountainhorse · Mar 8, 2018

HMMM 9%

Scott said:
Historically, Polaris has not published the horsepower rating but Marty Sampson told me that it was 9% more than 800.

9% is a pretty precise number....Not 10%

A "10%" number I would chaulk up to a guess as it is more of a general term.

So, With that said.

Can anybody tell me what Jim at Dynotech has Dyno'd a bone stock AXYS mountain 800 engine at for HP?
... And point us to the result or post up a chart?

With that.... we should have a fairly good number for this sled

Some examples

9% more on top of 150 HP = 164 HP

9% more on top of 151 HP = 165 HP

9% more on top of 152 HP = 166 HP

9% more on top of 153 HP = 167 HP

9% more on top of 154 HP = 168 HP

9% more on top of 155 HP = 169 HP

9% more on top of 156 HP = 170 HP

9% more on top of 157 HP = 171 HP

9% more on top of 158 HP = 172 HP

9% more on top of 159 HP = 173 HP

9% more on top of 160 HP = 174 HP

9% more on top of 161 HP = 175 HP

ETC.....

.

maurfello · Mar 8, 2018

mountainhorse said:
9% is a pretty precise number....Not 10%

A "10%" number I would chaulk up to a guess as it is more of a general term.

So, With that said.

Can anybody tell me what Jim at Dynotech has Dyno'd a bone stock AXYS mountain 800 engine at for HP?
... And point us to the result or post up a chart?

With that.... we should have a fairly good number for this sled

Some examples

9% more on top of 150 HP = 164 HP

9% more on top of 151 HP = 165 HP

9% more on top of 152 HP = 166 HP

9% more on top of 153 HP = 167 HP

9% more on top of 154 HP = 168 HP

9% more on top of 155 HP = 169 HP

9% more on top of 156 HP = 170 HP

9% more on top of 157 HP = 171 HP

9% more on top of 158 HP = 172 HP

9% more on top of 159 HP = 173 HP

9% more on top of 160 HP = 174 HP

9% more on top of 161 HP = 175 HP

ETC.....

.

Can't help myself

161 = 175 and a half

LOL

tdbaugha · Mar 8, 2018

There's also this: http://www.dynotechresearch.com/file_upload/page_files/DTRPolAxysPipeShootout.pdf

Which is after 2300 miles. Stock power was 154.1

mountainhorse · Mar 8, 2018

maurfello said:
Can't help myself

161 = 175 and a half

LOL

That's not the only only one... I rounded them all. :face-icon-small-win

.

mountainhorse · Mar 8, 2018

168.... not a bad number

So from that chart... Safe to say 168HP or maybe just slightly more.

The 850-Etec dyno'd at 167... so I'd say we're in the ballpark...infield.

Really gives me no reason to mess with the engine or exhaust.

.

icr · Mar 8, 2018

So about 5 more HP than a current 800 with aftermarket pipe

mountainhorse · Mar 8, 2018

ICR... which pipe alone is boosting the AXYS-mtn 800 HO power to 163 HP? (sincere question).

Also, I'm not sure that the aftermarket pipes retain the good-running-flexibilty in as wide of range as the stocker??

You post up some great info on here... so, I'm interested in your input.

.

10003514 · Mar 8, 2018

mountainhorse said:
So from that chart... Safe to say 168HP or maybe just slightly more.

The 850-Etec dyno'd at 167... so I'd say we're in the ballpark...infield.

Really gives me no reason to mess with the engine or exhaust.

.

Nice numbers from Polaris, hope they hold true on the production 850. Minor mods like the SLP pipe will easily put the numbers 175+. Be nice to see the torque numbers as well.

icr · Mar 8, 2018

The dyno tech graphs posted above show ssi at 163 and bmp at 162

mountainhorse · Mar 8, 2018

I think those are with timing and fuel changes tho (maybe just timing)

.

icr · Mar 8, 2018

mountainhorse said:
I think those are with timing and fuel changes tho (maybe just timing)

.

Why?

Spaarky · Mar 8, 2018

Scott said:
I can't wait to see how Turbotater does his 962 with this engine!

With the 800, he was taking his 910 big bore and building a custom (and expensive) 74mm stroker crank to make the 962.

And now he won't have to stroke it. He'll just punch the stocker out to a 962!!

Can't wait!

Motor is easy part. Fueling it is another and the 850 ECU is more complex than the HO.

JMCX · Mar 8, 2018

The 850 Doo is a torque monster. It may only have 10 more Hp at the peak than an 800 but at 6500-7000 it's like 30 more. I hope the Polaris is the same.

sledcaddie · Mar 8, 2018

new engine's cooling

So, the Pros always had a little problem with running hot when conditions were not adequate. That's why some of us opted for the standard RMK with 2 heat exchangers. Does this new engine's design help in this regard? Seems like I read somewhere about better heat dissipation. Also, has Polaris every had a standard 4 year warranty before?

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