we just drilled 4 3/4" holes on the bottom / and front as its curves down under of the chain case , picking up snow as you drive along. Actually the later TS cases have about enough snow coming in the back, they seem pretty good, I just decided to give it a little more, and Dan's ARO also.
Polaris RMK 800 snowbike
- Thread starter Brett Kobernik
- Start date
Cowboy it would be fun to hook up this winter. We can have the 1st rally for Frankinbike garage builds.
Nice Build. I like the bowls you used.
Nice Build. I like the bowls you used.
That’d be awesome. I love to see creations by other wingnuts.
Got another big piece of the puzzle figured out I think. Been working on the muffler. I’m trying to make an old KTM 520 pipe work.
Following advice from people who are smarter than I am, they suggested that I needed to test the flow on the stock silencer and try to match that in my custom muffler. Connect a shop vac to the inlet. Then stick a piece of tubing in the outlet.
On the other end of the tubing, you tape it to a wall to make a U shape and put some water in it. Mark it at zero. Turn the vacuum on and mark how far the water is pulled up the tubing. For reference, I also made a mark labeled “straight” where the water level is when sticking the tubing straight into the shop vac hose. You can see that there are some flow restrictions in the RMK silencer since sticking the tubing straight into the shop vac produces more vacuum than sticking the tubing into the silencer. I’m told I want to match the flow of the silencer.
Next I tested the stock KTM pipe. This was WAY different, as to be expected. It’s for a 4 stroke dirt bike. The outlet on the KTM was about half the size of the RMK outlet. So, I cut it out (curved pipe on glove in photo) and welded in a new bigger outlet pipe that’s the same size as the RMK outlet. Money. Same flow. Same inlet size. Same outlet size. This should work. I won’t be surprised if more tuning is necessary though.
Satisfied with the muffler, I mounted it and did the rest of the plumbing. Now that is a twisted looking exhaust system! Theoretically, I should have the same flow as the stock RMK. Same size expansion chamber, same flow through the silencer. We’ll see.
Following advice from people who are smarter than I am, they suggested that I needed to test the flow on the stock silencer and try to match that in my custom muffler. Connect a shop vac to the inlet. Then stick a piece of tubing in the outlet.
On the other end of the tubing, you tape it to a wall to make a U shape and put some water in it. Mark it at zero. Turn the vacuum on and mark how far the water is pulled up the tubing. For reference, I also made a mark labeled “straight” where the water level is when sticking the tubing straight into the shop vac hose. You can see that there are some flow restrictions in the RMK silencer since sticking the tubing straight into the shop vac produces more vacuum than sticking the tubing into the silencer. I’m told I want to match the flow of the silencer.
Next I tested the stock KTM pipe. This was WAY different, as to be expected. It’s for a 4 stroke dirt bike. The outlet on the KTM was about half the size of the RMK outlet. So, I cut it out (curved pipe on glove in photo) and welded in a new bigger outlet pipe that’s the same size as the RMK outlet. Money. Same flow. Same inlet size. Same outlet size. This should work. I won’t be surprised if more tuning is necessary though.
Satisfied with the muffler, I mounted it and did the rest of the plumbing. Now that is a twisted looking exhaust system! Theoretically, I should have the same flow as the stock RMK. Same size expansion chamber, same flow through the silencer. We’ll see.
This turbine looking thing is the baffle inside the KTM pipe. It would appear that this little obstruction is just enough to mimic the flow of the RMK silencer. We’ll see how silent this ends up being.
This exhaust task was a bitch. I ended up reworking the plumbing because I wasn’t able to easily assemble and disassemble it. Once I was satisfied (for the most part) I coated it with some high temp paint, wrapped it, and then coated it with silicone sealant.
I installed the aluminum guard over the heat wrap. I’m starting to close everything in with plastic now.
I installed the aluminum guard over the heat wrap. I’m starting to close everything in with plastic now.
Hey Brett,
I like how its coming together , looks mean and clean.
If you get out there riding the 2020 animal and trail manners seem less than friendly, make sure your ski mount bolt is at least 1 1/2" back towards the bike, 2" most times is better. That will immediately relax handling everywhere. I can't tell from your photo, but looks like the ski bolt is almost directly under the axle, and that won't be fun with any of the versions of timber sled skis.
I like how its coming together , looks mean and clean.
If you get out there riding the 2020 animal and trail manners seem less than friendly, make sure your ski mount bolt is at least 1 1/2" back towards the bike, 2" most times is better. That will immediately relax handling everywhere. I can't tell from your photo, but looks like the ski bolt is almost directly under the axle, and that won't be fun with any of the versions of timber sled skis.
Hopefully soon.Sound bite please , I really want to hear that turbine can on the snow
Thanks for that. Yeah, I believe it is directly below the axle bolt. I just set it up the same as The Unicorn because that bike handles real nice. I can make adjustments real easily and I'll probably play around with that once it's on snow.
I really think what you are doing is the way to go.
the bike I built with the engine behind the jackshaft had too much of the weight and gyroscope effect high up (above optimal Center of gravity) and behind the rider.
It was really hard to get the bike to lean when on the throttle.
the way you are setup will mimic a sled for gyro effect.
it also becomes apparent after blasting through a little brush that having some protection for your legs is really nice. ?
That pipe is awesome! I wondered how to get a shield back on a stock set up..... Wanna do another? ? I need to start hacking this 800r pipe up.... I always thought it would be cool to switch the engine 180, make it run backwards and have the pipe go straight out the back under the seat on a build like this. What made you use the ktm muffler vs just an aftermarket can from a Polaris 800?
I really hope so. It was a lot of “trial and error” and dumb-luck to get the astonishing results I did with the Unicorn last spring. I’m crossing my fingers that the Polaris project will exceed the Unicorn.
Well, I don’t know if I’d call it awesome but I think it will work well enough to start. I’m mildly satisfied but it weighs more than I like. The expansion chamber with the heat wrap and aluminum guard weighs 12lbs. The KTM muffler weighs 8lbs. 20lbs all together. There is certainly room for improvement here.
I chose the KTM pipe because A) I already had it, and B) it fit really nice where I wanted to mount it. Perfect fit actually. C) It seemed easy to modify to get the same flow rate as the stock can.
Do you have a build thread for that project of yours?
Did you ever weigh the unicorn? will this one be heavier?
Fat day in the shop. Got a good handle on the airbox. Started out with a thin gauge aluminum backing plate.
Then started cutting out sheet HDPE plastic to use as the box.
It’s a little rough but I think I’ll actually run this first prototype.
Next, I shaped a square intake passage and attached it to the box.
It fits easily to the throttle bodies. It’s a lot lighter weight than the stock intake system. I have a bunch more riveting and sealing to do but this is pretty much complete aside from a snow sock.
In the afternoon I tackled cleaning up the tunnel. The snowmobile rails add A LOT of structural integrity to the tunnel. Obviously, I’ve removed them. I decided to strengthen the bottom edge of the tunnel a bit by adding a piece of angle aluminum with ⅛” spacers between it and the tunnel. This stiffened things up nicely. I also added a gusset to the rear skid mounting bracket. I added some foot pegs that I stole from another machine.
I have most of the plastic covers finished. I still need to dial in a few fasteners as I finish the project. The beast is really coming along!! I still have some more mechanical stuff to do under the hood.
I weighed the Yamalaris tonight. 400lbs. I’m not quite as happy with that. That’s only 31lbs lighter than the original RMK. I was hoping for 50lbs lighter, at least. This is still possible with a fancier exhaust, aluminum bar risers, and a few other custom parts. Overall, I’m pretty happy right now. I’m thinking this 140hp snowbike with the full size track is gonna be nuts. If I could trim it down to the 360-380lb range, I’d be really psyched.
Then started cutting out sheet HDPE plastic to use as the box.
It’s a little rough but I think I’ll actually run this first prototype.
Next, I shaped a square intake passage and attached it to the box.
It fits easily to the throttle bodies. It’s a lot lighter weight than the stock intake system. I have a bunch more riveting and sealing to do but this is pretty much complete aside from a snow sock.
In the afternoon I tackled cleaning up the tunnel. The snowmobile rails add A LOT of structural integrity to the tunnel. Obviously, I’ve removed them. I decided to strengthen the bottom edge of the tunnel a bit by adding a piece of angle aluminum with ⅛” spacers between it and the tunnel. This stiffened things up nicely. I also added a gusset to the rear skid mounting bracket. I added some foot pegs that I stole from another machine.
I have most of the plastic covers finished. I still need to dial in a few fasteners as I finish the project. The beast is really coming along!! I still have some more mechanical stuff to do under the hood.
Funny you mention that. Yes I did weigh the Unicorn last week. I use a crude method because it’s all I have. One bathroom scale under the ski, one under the track, add the results. It gives a pretty decent rough number. The Unicorn came in at 375lbs, no fluids. I’m pretty happy with that. The thing is pushing 90hp. It’s 140lbs lighter than the Powder Special that engine came out of. (yeah, 1995 sled technology, I know, big deal)
I weighed the Yamalaris tonight. 400lbs. I’m not quite as happy with that. That’s only 31lbs lighter than the original RMK. I was hoping for 50lbs lighter, at least. This is still possible with a fancier exhaust, aluminum bar risers, and a few other custom parts. Overall, I’m pretty happy right now. I’m thinking this 140hp snowbike with the full size track is gonna be nuts. If I could trim it down to the 360-380lb range, I’d be really psyched.
Cool build, look forward to seeing it in action. To reduce some weight could you get some heavier fork springs and ditch the giant coilover? Or is there too much weight up front to carry with the bike forks alone?
The yamalaris should do well though with that much track and hp it's hard to go wrong. You can waist time making it lighter later. My raptor is about the same weight and I put .54 springs in the fork and they might be a tad stiff now because most of the weight is on the track with the yamalaris it could work too without the trio.
This thought has been going through my head since I bought these third shocks last season. I really want to get rid of that third shock. But let me tell you, after riding one, I'm fully addicted. It is much, MUCH better than just stiffening up the forks with heavier springs and/or heavier oil. The ride is soft and plush with no bottoming. I'm totally blown away. Perhaps a suspension guru could figure out the right balance of spring rate, valving and oil weight/level in the stock forks.
The front scale on the Yamalaris came in at 160lbs. The rear scale was 240lbs. Seems like a person should be able to get just the stock front shocks to do what we want.
Exactly my thinking.
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