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Home > Technical Articles
Stage Tuning the 800 RMK
By Jerry Matthews

January 1999:

Rumor flies of an all new 800 domestic twin from Polaris.

March 1999:

Polaris offically releases an 800 twin to be only in an RMK chassis in very limited numbers. Horsepower is not quoted but said to be approximately 10% higher than the 700 twin. Interest is high on these models and most dealers sell out of them within days of opening up the snow check program. Even considering the popularity of the 800 twin, the 700 twin retains much of its following due to extremely high customer satisfaction and the limited availablity of the new 800 twin.

April 1999:

Prototypes of this all new 800 twin hit the snow in several dealerships throughout the West.

Summer 1999:

Coffee shop chatter relating to how well this 800 twin is going to work in the mountains is commonplace. Friends (or skeptics as they are also known) riding different brands are quick to argue how their brand sled will not be beat by this new "Black Beast".

October 1999:

Production 800 RMK twins hit dealerships.

The Polaris RMK 800 has been one of the most highly anticipated and sought after models to be released in the past several years. Since 1997, the 700 has been targeted heavily by manufacuters, aftermarket as well as OEM. These snowmobiles, lightweight twins for the most part, have offered a wonderful power to weight ratio while delivering high torque and broad power bands. These big twins have not normally been as fast as the triples are in a drag race on flat ground, but point them up a hill and they really shine. Many have wondered if life can ever get better than it has been with the lightweight 700 twins.

Upon release, this new 800 twin motor was claimed to made 10% more horsepower than the 1999 700 Polaris twin. We found that the Polaris 700 made 118 H.P. while the 800 twin made 127 H.P. (Both in stock form) which equates to a 9 H.P. increase, approximately 8% higher than the 700 twin. However, if you look at the torque increase, the 700 made 77.6 ft lbs of torque at 7800 rpm (peak torque) while the 800 twin makes 86.3 ft lbs of torque at 7400 rpm (peak torque). This equates into an 11 1/2 % increase in peak torque. Torqueis the key issue to mountain riding. Having a high torque motor with a faitly flat torque curve (the 800 twin looks like a four stroke torque curve) makes keeping the motor running at its peak extremely easy. This motor will require very little tinkering to keep it at its peak as conditions and elevations change. The 800 twin has a much broader powerband than its predecessor, the 700 twin, and will therefore make a better mountain sled. In fact, if you compare the 800 twin to a 700 twin, you will notice that the 800 has over 50% more horsepower than the 700 in the low end (@ 5700 rpm). The difference through the entire low en and midrange is a solid 15 to 20 horsepower. This sled (800 twin) is like a tractor! It has a great bottom end that will make it extremely easy to (boon dock)through the trees as well as good top end which will make hill climbing a synch. It looks to be one of the best stock powerplants to ever be manufactured for mountain riding.

Stage One- SLP Single Pipe

A single pipe was the natural place to start on this 800 Twin. Our goal was to give the motor more peak horsepower with a wider power band and reduce weight. As you a can tell, we increased the torque substantially throught the entire spectrum, which turns into an increase in horsepower. The power peak came down about a 100 rpm (7800 rpm) and gave a 200 rpm wide power peak (7700 to 7900 rpm). Peak horsepower increased by 8.7 h.p. (from 126.5 to 135.5) and there was also a very substatial gain in low end horsepower (+12.4H.P. @6500 rpm). This is a very user friendly combination that will require very little tunning to keep the motor running at its peak. All of this was achieved with near stock sound levels delivered though the implementation of SLP's Era 2000 Silencing Technology. One will notice the all new clamshell type sheild which serves two purposes; it keeps heat in the pipe to stabilize running temperatures as well as reducing sound emmisions (it also looks nice). You will also notice a resonate chamber located on the outlet of the silencer which helps further reduce sound levels. Even with all of these additions to hold noise levels to a minimum, this SLP single is 6 pounds lighter that the OEM pipe. It comes with a new Y-manifold, pipe and quiet silencer. The price of this product is $399.00.


Stage 2-SLP Twin Pipes

On we went trying to make this motor really put out some big horsepower and torque numbers. Our goal was to push the peak torque numbers up, ultimately increasing peak horsepower, in order to give this motor its full potential with the stock porting and no other engine mods. We still wanted to keep a broad power band and shed some weight. Usually when you add horsepower to the peak, you compromise some of the bottom end and midrange. However, with this motor, we were very pleased to be able to better our single pipe everywhere except for just off of engagement and in one 400 rpm spread in the upper midrange (7400 to 7800 rpm). You will notice that in the lower midrange this pipe gives an average 19 h.p. gain (6100 to 6700) over stock. At its peak (8100 rpm), this set gives an awesome 18.5 h.p. gain (126.8 to 145.3 h.p.) while only pushing the peak up 100 rpm. Like the SLP single pipe, it offers quiet sound levels and lightweight. At first glance you will notice three resonate chambers on the outside of the silencer. These are used for sound reduction purposes. The pipe set gives a 1 pound weight savings. The Price of this pipe set is $519.00.


Stage 3-SLP Twin Pipes and Billet Heads

After adding twin pipes, we decided to apply some of the combustion technology we have been developing over the last 15 years with our Billet Heads. Our goal here was to give the motor some more peak horsepower as well as boosting the bottom end and midrange power to give sharper throttle response. Peak horsepower was only increased by 0.3 h.p. (145.3 to 145.6 h.p.) however, they brought the power peak down 100 rpm which in turn increased peak torque. This helps keep the motor on the power peak better as conditions and elevation change. Also, through the bottom end they gave an average 3 h.p. increase (6800 to 7100 rpm) and it provided an additional 4 hp average increase through the upper midrange (7300 to 8000 rpm). This will give the sled great bottom end throttle response. The heads cost $279.00 bringing the investment of Stage 3 up to $798.00.

Stage 4-
SLP Twin Pipes, Billet Heads and SLP High Flow Air Box Conversion Kit

We felt that it was high time to let this baby breathe. In the past, the High Flow kit added substantial horsepowerimproving items added. Stock air boxes are designed to flow only as much air as the stock motor demands. When you add horsepower products which give you substantial gains, you add demands for intake airflow. By installing out High Flow air box kit we acquired a gain in horsepower from 6400 rpm up wiht an average of 3.5 h.p. from7200 to 8100 rpm. You will notice that it broadened out the horsepower peak to about a 300 rpm spread (7900 to 8200 rpm). Peak horsepower was improving by 2.7 h.p. (145.6 to 148.3 hp) after adding twin pipes, this is the best horsepower for the dollar spent. The High Flow Air Box Conversion Kit costs $79.00 bringing the investment of stage 4 up to $877.00


Stage 5-SLP Twin Pipes, Billet Heads, SLP High Flow Air Box Conversion Kit and V-Force Delta Reeds

V-Force Reeds have usually been good for a gain in the past, and we felt if was time to see what they would do for this 800 twin. As you can see, they were good for 2.5 hp increase at the peak (8000) as well as broadening the power peak. The horsepower came up to 150.8 for a 200 rpm spread (7900 to 8100 rpm), the motor is making almost the same power. Torque is very high as well. At 7900 rpm we are seeing almost 100 ft lbs of torque. Set up like this, this motor will be a very fun, user friendly setup. The cost of the V-Force Reeds are $258.00 and brings the investment of Stage 5 up to $1135.00.


Stage 6-SLP Twin Pipes, Billet Heads, SLP High Flow Air Box Conversion Kit, V-Force Reeds, and Trail Porting.

Feeling that the motor was about at its potential with its mild porting, we decided to grind on the cylinders and put the special SLP touch into the ports of this motor. Our goal here was to cut on the ports just enough to allow for more flow on the peak but not so much as to killthe bottom end and midrange torque and horsepower. As you can see, we did lose some horsepower throughout the bottom end and midrange, however, we kept the loss minimal and were able to achieve a 7.9 h.p. increase at the peak (150.8 to 158.7 h.p.). We pushed the power peak up 300 rpm but were able to keep a nice wide power spread at teh peak (8200 to 8500 rpm). This combination will be very fast and extremely fun, but due to a certain amount of low end and midrange torque and horsepower to recieve the gain at the peak, it will not have quite as good of throttle response as Stage 5 did on the low end and through the midrange. The cost of the Trail Porting is $425.00 and brings the investment of Stage 6 up to $1560.00.


In an effort to get some of the bottom end and midrange horsepower back, we tried our single pipe instead of the twin pipes in the Stage 6 configuration. We only saw a gain over the twin pipes in the 7600 to 7900 rpm range which was an average of 5 h.p. This combination peaked at 147.3 h.p. at 8100 rpm. It did have a broad powerband but we felt that for the money spent, you would be happier with Stage 4 which had a little more peak horsepower with much more bottom end and midrange power.

For those of you who want even more horsepower than Stage 6, we offer upper half Crankcase Porting which adds another 3 h.p. peak. We are currently working on Trail Mod Porting which we expect to take the peak horsepower somewhere in the mid 160 h.p. range. We will also have high compression versions of out Billet Heads to give even better throttle response to these combinations. The addition of Trail Mod Porting or high compression Billet Heads will require the use of 50/50 race gas/premium mix.

Due to all of the additional power that has been added, each of these combinations will require some clutching and jetting deviation from stock in order to receive the full potential out of this motor in the field. Because the high torque of this motor creates a broad power band, we feel that the tuning will be very consistent.

One word of advice is that this 800 motor likes good fuel when modified above 148 horsepower. We found that the ratio of 1 gallon of race fuel to 4 gallons of 91 octane premium fuel was a good ratio. Also, if you find detonation symptoms present with your motor or fuel that you are using, flip the the premium switch to regular ( on the key switch) and it will normally take care of it. This is a handy little way to retard the timing so that no performance loss or engine damage is experienced.

This 800 twin motor looks to be one of the best powerplants that we have ever had our hands on. It displays very high torque and horsepower and will about rip your arm out of their sockets when you grab a handful of throttle. We have put much effort into this project in order for you to have performance options available when it snows. We are confident that this 800 twin will put a smile on your face so big that you will still be wearing it this time next year.

"Setting the World's Performance Standards"