As you know though these machines have no O2 sensors or closed loop capability. I thought it was common knowledge,or at least a long standing rumor lol,that the 800s do run rich in stock form. The 850s broke the Polaris mold so to speak,they do not run on the rich side from the reports I have seen from dyno runs.
In addition to displacement and weight there are other factors as well, effective gear ratio( which I mentioned above) the engine's volumetric effeiciency(2 eninges of the same displacement can have very different fuel requirements for the same AFR,even 2 cyl of the same engine can require different fuel volumes),parasitic losses(ie driveline loss) ect.
But in this case gearing and tunining are good bets IMO...whatever the cause there is a pretty good case for saying the 850 does better than most of the Polaris 800s,maybe yours has a small vacuum leak lol. J/k

I have a little tuning knowledge,mostly Fords...why are you running open loop during part throttle? Choice or necessity,ie aftermarket fuel controller? I used the stock Ford ECM and somewhat normal O2 operation for closed loop on my 1000 HP Twin Turbo Cobra...Never checked mileage around town but it got 23-24 on the hwy (as long as you stayed out of boost lol.)

Ok..whoops I got side tracked.

 

So, back to the subject...... If you are trying to decide between the 800 and the 850, get the 850.

For my riding style the 850 gets considerably better mpg's. And then there is all the other advantages compared to the 800. Ride both, then decide.

As for the open loop tuning on the WS6, probably running aftermarket tuner set with a wideband. Not the most economical for a daily driver but very user friendly and adjustable for boost and other power adders.

As for the twin turbo Cobra.............I wanna drive it! (jealous).

 

The 800 Sportsman has a smaller 4.1 gal tank then the 300 Sportsman's 4.5 gal tank which is just crazy. So comparing riding range with the 5.25 gal 850xp is not really fair.

What is also crazy also is our dealership sells 800 Sportsmans for the same price and 750 KQ for $200 less than a mid bore xp550.

 

It's set up basically as a street car...full interior,AC ect...one word it is SCARY, it will light up 315 DRs at 80+ MPH lol....

ok...ok..ok...easy to get me off topic when talking cars.
Back on topic..850...850..850 lol.

 

What the......Who owns a 1000hp Cobra. That is simple madness.

 

Well I DID,I build them race 'em a little and sell then build another. I'm on hiatious right now...too many kids at the moment lol.

Here's my last one.....pure retarded..lol



Here is an 889 RWHP pull @21psi on a Loaded Mustang Dyno during tuning up in PA...ran out of MAF at 6500 RPM on this pull with a SCT BA2800 MAF AND a MAFia lol. Look at the HP still climbing to the Sky
Twin 61MM BB watercooled turbos..billet rods,CP pistons...balanced and blueprinted,custom fuel system ect ect ect..set up is good to 30+ pounds of boost..with enough MAF.
A street car faster than any one would ever need...

 

Madness.....Can't even imagine a street car like that. I'd be like having a $10,000 an hour prostitute every night. How could you go back to normal.

 

running open loop basically because i get annoyed with fuel trims screwing with my tune(long tube headers dont work too well with the stock old 02 sensors). Data logging showed me that with my tune in open loop i had no more then 2% error then commanded AFR at any point so i figured why bother with closed loop. Using HPTuners software. love it.. best thing i have ever bought for my car.

Those cobras sure do have a built engine from the factory... I toyed with the idea of moving to a F1 procharger or a big single turbo but honestly... on the street 600+ rwhp is more then plenty and i dont drag race it competitively . If i lived out in arizona or something like that id give this forged ls1 a healthy mix of fuel and air! At our last dyno day there was a camaro that had a single t88 kit with a stroked 6 liter (402ci) running only 15 lbs of boost and made 780rwhp.... just sick, that t88 wasnt even breakin a sweat @ 15lbs and no lag!

Just wondering the MAF is the first thing to go on a GM and run in speed density... is the maf too far integrated into the computer to ditch it with ford?? speed density tuning is sooooo much nicer....

anyways..

as far as my 800 popo to get somewhat back on topic... lol... If i have a small vacuum leak i hope it doesnt change!!i get great gas mileage and im not complaining!

Has anyone ever determined if different years had different programming in the computer for the fuel curve?