Four-stroke Pro's

Kachess1 · Mar 26, 2019

Built 2 more naturally aspirated four-stoke Pro's this year and have a winter's worth of riding on all three. Have $2500 to $3000 into each of them since we all already had RX1 motors to donate. Reasonably simple swap. No machining, simple wire feed welding. Fortunately cheap clean Pro's with blown motors are easy to come by. We have them on 2016, 2014, and 2011 chassis's and they run head-to head with their 2-stroke brothers. My 2016 RMK 457# before, 469# after swap. Motors have anywhere from 5k to 14k miles on them but all run strong/identical. Next step is anti-ratchets: have to run tracks crazy tight. Fuel injected; improve running on steep downhill carves. Try a 163in Track. Very fun!

Here's riding in McCall last week. https://youtu.be/9y4tFI1D03Y

turbolover · Mar 26, 2019

So what motors are you putting in them? Pretty neat to see someone doing something different from the crowd.

About the only real drawback I can see on that is when you get stuck, you probably don't want to get that 4 stroke on its top.

I usually end up with my sled upside down to get it unstuck at least a couple of times every ride.

Kachess1 · Mar 26, 2019

We typically roll our sleds out of stucks at least a couple times per ride. The RX1/apex motor has a dry sump so most of the oil sits in a reservoir. The little oil in the crankcase can run out the breather tube into the airbox when upside down. Only good thing about our carb versions is they shut off when they go upside down so we don't toast motors. We can roll out 3 or 4 times and not go low on oil. I have installed a solenoid valve on the breather before but feared it might malfunction and I don't want to build crankcase pressure. Been rolling them out for 15 years. A little oil out the belly pan once in a while is not a big deal.

Norway · Mar 30, 2019

Way cool. Congrats on some fine builds. They do sound awesome and if the weight penalty is only around 10-12lbs, kudos for a good quality build.

Sent fra min S60 via Tapatalk

jim · Apr 1, 2019

Turbo any of them? How is the handling compared to a stock Pro? I found the Apex to be very heavy front handling.

Kachess1 · Apr 4, 2019

We've ridden lightened RX-1's 159's (less 80 lbs from stock) for years and have been able to make them go most anywhere. The yami motor in the pro chassis is another 60lbs lighter and massively more maneuverable. We are still learning what they can do. They're super easy to lay over, can hang a crazy steep sidehill and downhill carve like nothing we've ridden. The video has some sidehilling. Unfortunately none of have experience with stock pros. Our chassis's had blown motors. I guess our next step will be to let an experienced pro rider run them side by side.

TRS · Apr 4, 2019

Kachess1 said:
We typically roll our sleds out of stucks at least a couple times per ride. The RX1/apex motor has a dry sump so most of the oil sits in a reservoir. The little oil in the crankcase can run out the breather tube into the airbox when upside down. Only good thing about our carb versions is they shut off when they go upside down so we don't toast motors. We can roll out 3 or 4 times and not go low on oil. I have installed a solenoid valve on the breather before but feared it might malfunction and I don't want to build crankcase pressure. Been rolling them out for 15 years. A little oil out the belly pan once in a while is not a big deal.

I know an old boy that has that oil loss issue fixed. Send me a PM and I’ll give you his number.

Kachess1 · Apr 7, 2019

Thanks for the tip. As far as Turbo's in any or them, not yet. There is plenty of room alongside the motor but I'm thinking the Apex fuel injected motor is a better candidate. We messed with MCX and Bender rear mounts on our RX1's but they added a lot of weight and we had to constantly fiddle with them. Another summer project will be seeing if we can get the Apex fuel injection rails to fit. Clearance between the motor and the steering link is pretty tight.

TRS · Apr 7, 2019

Kachess1 said:
Thanks for the tip. As far as Turbo's in any or them, not yet. There is plenty of room alongside the motor but I'm thinking the Apex fuel injected motor is a better candidate. We messed with MCX and Bender rear mounts on our RX1's but they added a lot of weight and we had to constantly fiddle with them. Another summer project will be seeing if we can get the Apex fuel injection rails to fit. Clearance between the motor and the steering link is pretty tight.

The gent I sent contact info on, can help you in the turbo dept also.

macsummit · May 24, 2019

They look good anymore build pics or information on them very nice job

NHRoadking · May 25, 2019

What's the hp difference between the Poo 800 and the Yammy?

How is it that the difference in weight only came to 12 pounds?

sno*jet · May 25, 2019

very cool. love the sound, looks a lot more torque than a 2stroke. maybe could use a little bigger paddle but works great. I want!

MKULTRA · May 26, 2019

NHRoadking said:
What's the hp difference between the Poo 800 and the Yammy?

How is it that the difference in weight only came to 12 pounds?

chassis is lighter

NHRoadking · May 26, 2019

MKULTRA said:
chassis is lighter

That's impressive then.

Motorbreath_ · May 26, 2019

Kachess1 said:
My 2016 RMK 457# before, 469# after swap.

Just so we are clear..

So the overbuilt 4 cylinder RX-1 engine is only 12 pounds heavier than the Polaris 800 twin?

:face-icon-small-con

SNWMBL · May 26, 2019

The 3-cylinder FX Nytro motor is 112 lbs with flex joints but no oil or coolant. I believe the 4 cylinders are 12 lbs heavier. My guess is there are some other lightweight mods done to these sleds. Very cool though.

Killer Time Racing · May 29, 2019

Imo .... They sound and look WAY to high geared !!!

Sidehilling is done slow and with way less track speed than that .. with the torque those have you should be able to pull up to that hill like you guys are and at a stop hammer the throttle and bury it to the boards .. like instantly.

Most people change their clutching so it will not trench but it is done with less spring pressure to let it engage sooner ..

Cut them Grab handles off and turn the skis the wrong way along with your weight in a field and it will flip on it's side if you have your weight and throttle correct. Then find the spot you can balance your weight against the power to keep it in a big circle ... After that I'm betting your sidehilling will seem natural.

Then you will find you need to apply more throttle to keep the track spinning to maintain a good trench to settle into. As you continue along the hill foot placement is crucial. To far back you will go up hill and get stuck, to far forward it climbs out of the hole and goes down the hill ... So it's done a hundred ways but everyone does it at a slow pace or usally goes flying down the hill or give up and go up it !!!

Of course this is totally in my own opinion.. I'm from Michigan so I'm not a lifer !!

Kachess1 · Jan 24, 2020

Into our second winter with 3 Polaris Pros w/4-stroke powerplants. Headed to Revelstoke on the 5th. Weighed my sled with 7 gallons, which is "ready to ride" for us. Gives us 70 miles which is twice a typical day for us. Our wet weight is a hair less than the 2019 Doo 850 154, wet weight of 551lbs. Frustrating the manufacturers don't produce a competitive 4-stroke when we can in our garage.

2019 Wet weights, Sidewinder 643lbs, Skidoo Summit sp 850 154, 551lbs, Pro 3in. 155 519lbs, Arctic Cat Alpha 154 at 540lbs.

Kachess1 · Jan 24, 2020

Motorbreath_ said:
Just so we are clear..

So the overbuilt 4 cylinder RX-1 engine is only 12 pounds heavier than the Polaris 800 twin?

:face-icon-small-con

The Polaris motor was 91 lbs, and the Pro pipe was 23.5 lbs. The RX-1 motor is 128 lbs and stock sleds dyno at 142. Ours have pretty straight pipes and seem to pull pretty hard. Consistantly out drag doo 850's. Not out climb, though.

Mpaine · Mar 15, 2020

What did you use for a chaincase on these. I'm thinking about putting a sidewinder motor in a axys pro!

Four-stroke Pro's

Enduring the heat till Braap Season

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