Any improvements we can make to airflow wil help our net HP number get closer to the gross HP rating.

 

<div class="FTQUOTE"><begin quote>Originally posted by: HIGHOCTANE

<div class="FTQUOTE"><begin quote>Originally posted by: DODGE57HEMI



This equals to about a 45-46% loss of HP in the drive train, and average everday car with a traditional automatic looses about 15-20% in drivetrain HP but if you look at a typical big bore ATV with a belt drive tranny I think that these #'s are about right where they are suppost to be. If you takin the fact that they are belt driven with IRS there is multiple places for power loss like this. If you were to have two identical engines one in a Sport quad and a ute I gurantee that the Sport quad will have mor HP at the wheels with a manual tranny, chain dr and solid axle. In short I think it is spot on!</end quote></div>





Have you seen dyno numbers from a CVT utility ATV? 45-46% loss is HIGH....those numbers are not spot on IMO for a machine that makes 70HP at the crank...

But as I have said dyno numbers are only comparable if the variables are the same..we need more info to judge the numbers...

Do I think the XP is overrated..no ...but I do think that there is an issue with those numbers..</end quote></div>
I think that that % of power loss is kinda high too but with him having bigger tires that kinda explains it but it is still kinda on the high side IMO!

 

<div class="FTQUOTE"><begin quote>Originally posted by: WOLF1

<div class="FTQUOTE"><begin quote>Originally posted by: HIGHOCTANE



<div class="FTQUOTE"><begin quote>Originally posted by: DCT

Looks like I need to tear mine open and see if I can port match some... I opened the airbox by removing the hood and installed a k&n and noticed a good improvement..










No such luck on the 850....not that it is slow..but I'll take free HP any day on anything lol..I looked and best I can tell the throttle plates open fully....



I'm still tweaking the Airbox mod,air filter,exhaust and Optimizer combo..</end quote></div>





The throttle plates do open all the way. However there is alot of room for improvement in the area of the throttle body.

The port match up between the head and intake is pretty poor, luckily there is enough material in the intake that matching the ports is possible.

The throttle body bore is 40mm but the port it mates to on the intake is 42mm and the port size of the plenum is 38mm. Ideally the throttle body should be bored to 42mm or at a minimum tapered out to 42mm and the plenum can be ported to match.</end quote></div>

 

These at the crank readings throw everyone off.The belt drive curse they do suck up a lot of power.

 

<div class="FTQUOTE"><begin quote>Originally posted by: scrambler400enoge

These at the crank readings throw everyone off.The belt drive curse they do suck up a lot of power.</end quote></div>

There is also a big difference between Gross and Net HP.

Most Gross HP dyno tests are run on hand assembled engines with a very "hot" tune, add to that the dyno exhaust and intake configurations.
Production engines are usually "detuned" slightly for durability, plus we have the added restrictions of airbox/exhaust that most often are limited by application "space" and weatherproofing/noise emissions.

This is normal. All manufacturers advertise peak gross HP numbers. The auto industry is a little more accurate as they are monitored a little closer, but its still there on performance models where numbers sell.

I do not doubt that the 850 is rated at 70 HP. However, as with ALL models from every manufacturer Gross and Net are different.

It gets complicated from here. For example: When we add a performance exhaust we dont suddenly have 75HP, we have simply picked up 5hp that the manufacturer "left on the table" from Gross to Net.

When tuners build performance accessories they work off the same principal.

 

The 850 in stock form runs like a cat with its @ss on fire! I was personally pleased to see the low HP numbers at the wheels, this means that the manufacturer left a lot "on the table" performance wise and we can access this hidden potential without internal engine mods. I would guess the "Net" HP to be 55-60 which means 10-15 HP are available with aftermarket exhaust and intake components, as well as cleaning up all the production errors such as port misalignment and tuning.

On a side note: As a general rule the larger the displacement the more potential is hidden within.
For example: Looking back at my racing and sand dune days, why would a Honda CR500 not have double the power of a CR250? Tear each down and you will see the difference in attention to details.

Rant over..............

 

There are also several different ways to measure HP at the crank...... net HP and brake hp (BHP) are totally different numbers...... The only ones that are "real" are what is at the rear wheels on a roller tension type dyno.

The fact that a Polaris 850 has almost 40hp at the rear wheels is probably about right. And that is a good amount of power hitting the ground for an 800 pound machine. But the number that you should really want to see on something that heavy is the torque, because it is the torque that is going to get you up and going on a machine that big.....

As the old saying goes, torque it what gets you going, HP is what keeps you pulling. Given the way that big machine moves I'd venture to guess that the torque numbers are quite impressive from a 850cc thumper.

 

yeah what are the torque #'s ??

 

To add...IMO chassis dynos are only a tool,and really only for that machine on that dyno..with the same tires each time,to measure improvements on that machine..evey dyno(and especially form different manuafcuters) will show different numbers..Generally Superflow and Mustang dynos will give lower numbers than a Dynojet....
There are alot of variables involved,the operator settings in the software can affect the numbers,Tires can make a signicant difference,not only because of rotational mass,but tracion on the rollers as well..
Also you have different correction factors..SAE,STD/STP...they will all net different corrected numbers...
Also the CVT will affect the numbers as it is constantly shifting,no way to lock it into a gear...when dynoing most machines,cars for expample,they are locked into a single gear...
This will likely greatly affect dyno numbers,and while that doesn't mean it is ineficient it could appear that way because the CVT is upshifting as wheel speed increases..
For example on a car you dyno with the tranny in 4th gear(or whatever gear is 1:1) and it stays in that gear for the entire pull...not the case with the CVT...
Again I think that there is settings in the dyno software to compensate for that but I'm not sure of this,i know lot more about dynoing cars that ATVs'..if that is the case,there goes another variable...as every dyno manufacturer seems to complesate for certain variables different ways,and on alot of them they operator has leeway on how to apply the compensation. I have a friend that owns a superflow..I'll have to ask him.
This might explain rumors i have heard of gaining 10% peak power on a dyno just with a clutch kit...it isn't making anymore power,and might not be anymore efficient..it is likely just fooling the dyno in essense...

Then there is loaded vs. unloaded dynoing...which is a whole other set of variables that can be minipulated...
So really unless you run 2 machines on the same dyno under similar circumstances(temp humidity and baro pressure) the results are pretty useless for comparing the 2 machines..

Unless we know what standard manufaturers are using for testing,such as SAE,if any,there advertised numbers don't mean much. BUT you would think the CARB numbers would be done with some sort of standard,since the allowable emmisions are based on power output.

Just my 2...

 

I heard that for every gear mesh there is about a 4% loss. Not sure if that helps any.