Snowbikes and Big Bores

Cooksend

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After many years as a sledder I spent this season with just a snowbike. Have to say I am now a convert and so the fun begins. One hot topic is always how can I get more power? How can I get reliable power?
I have many plans for this off season to improve my set up and 1 of those is power! I ride a 2015 Husky 501. ECU was not locked and I had the Euro Map installed as well as map switch. This winter I also had Blais Racing update my ECU. It ran great this year however I would love a bit more!

What are your experiences with Big Bores for Snowbike applications?
 

wwillf01

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After many years as a sledder I spent this season with just a snowbike. Have to say I am now a convert and so the fun begins. One hot topic is always how can I get more power? How can I get reliable power?
I have many plans for this off season to improve my set up and 1 of those is power! I ride a 2015 Husky 501. ECU was not locked and I had the Euro Map installed as well as map switch. This winter I also had Blais Racing update my ECU. It ran great this year however I would love a bit more!

What are your experiences with Big Bores for Snowbike applications?
My experience is it's best to go cams, porting , high compression piston dyno tune with someone good. On my 450sxf I am hovering around 70hp and now have 60 hours on it this season stone cold reliable... that's my opinion.. if i would have gone full race gas I could have reached upper 70's but i did not want the expense ... I have known people with good luck and bad luck on big bores.....most likely like everything comes down to the builder. I like keeping the free reving nature of the bike and lots of over rev ....

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Jan 14, 2004
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Thumper Racing built my big bore twice and it blew up twice. They flat out Fawked me over, a-holes. Big bore is a waste of time and money. Stick to cams etc as mentioned. In the end it really doesn't matter, you get more by improving your riding skills then you will by mechanical improvements, a bike will never be a point and shoot. All my friends who went down the big bore rabbit hole are back on stock bikes. Stock rocks.
 

yooper01

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I had thumper racing build two big bores for snowbikes for me, one rfs 570 with high compression piston and one xc4 motor too.

I sold both around 60 houra and now both have over 100 with nothing done to them but oil changes.

Both were awesome. The rfs was an animal and smoked every 450 mx bike in my group, but all told I had like 3500 into that motor, it started out as a 01 520 sx 4 speed and morphed into a 570 with Cam, hich comp piston, 6 speed tranny, welded crank, and a electric starter.

M5 and I had two opposite experiences.




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portgrinder

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Seen some ultra high effort motors ran, and the best ones get into 60-65 range. What you get is more usable rpm, not a huge peak number. Ie larger rpm range where your making good power

Big bores sell because they are easy. Any brain dead guy can hog out a cylinder, replate it and find a piston to fit. and people love em. 2 or 4 banger is all the same. In reality it’s usually everything but the bore that needs to change to make power.

When you cross over from a sled you think you need more power. Cheaper to listen to the guys on here who have already done it.
 
Nov 28, 2007
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It makes way more sense to fine tune your kit so the power gets to the ground.

Just like on sleds it is the guys with al the engine mods that always blow up and seldom have a
dialled drivetrain. Light weight and dialled is the winning combination. 450s work better than the 500s due to a much wider rev range with ecellent top end. At 60 HP them bikes are pretty strung out much more just reduces reliability. I rather ride a bike I can wring out without worry than have one that has 5 more Hp where I have to worry about holding here to the pin.
 
Nov 14, 2017
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I have a Thumper Racing 520 kit and I absolutely love it. I have lots of hours on it and it has been fantastic. My complaints aren't with reliability, however the vibration and lowering of the torque curve are negatives that you have to deal with.
 

GKR

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This is an interesting watch for some theory around bore size and big bores.


This season I did a Thumper Racing 520 kit in a 2015 KTM and it works fantastic. Not a ton of hours yet but so far runs perfect. The lower torque curve allows you to pull another gear from the stock 450 in almost all circumstances. I don't find this as a negative at all, maybe an adjustment to riding style a bit, but I would rather not wring it out all day but rather use the torque at a lower RPM. No downside that I can see at this stage.
 

needpowder

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When I rebuild my top end at the end of the season I will be adding a high compression piston/cylinder kit. Makes up a little bit for riding at high elevation and is still as reliable as stock. Reliability is crucial in the mountains. I would love to have more power but I don’t really care about getting 2-5 more horsepower. I want 50 more horsepower no, make that 100.
 

wwillf01

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You are so close to proven moto I would check out their snowbike package... they have been building some stone cold reliable power...

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Proven Moto in Heber has built me a couple motors. I ride KTM 450's and he has made a ton of reliable power for me. Stock these bikes are fun. But with a little massaging those are a blast and you can carry a much higher gear even in deeper Utah Fluff. You just need to decide how much you want to spend. but the key is fresh fluids every other ride if not every ride.
 

wwillf01

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Agreed... I find the added power gives you the ability to not wring the crap out of the engine and have a much longer range of power to play with. I stopped bouncing off the rev limiter as much...

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EXO Sled

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If you’re looking for reliable powerful snowbike, there’s a solution... at least 160 hp full injection...
 

Cooksend

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If you’re looking for reliable powerful snowbike, there’s a solution... at least 160 hp full injection...
Been riding sled most of my life, Snowhawk for a few years and now addicted to the Snowbike. Many years ago I wondered what it would be like to have a mono ski sled. Concept was awesome then just not sure it's what I want today. Any Demo Days?

Great work BTW!
 

wwillf01

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Does look cool.. but I want less weight that's what draws me to snowbikes.. but having something designed engine wise for the snow would be super easy...

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EXO Sled

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Been riding sled most of my life, Snowhawk for a few years and now addicted to the Snowbike. Many years ago I wondered what it would be like to have a mono ski sled. Concept was awesome then just not sure it's what I want today. Any Demo Days?

Great work BTW!
We went to Revelstoke in February for demo ride. This winter with COVID situation, all other demo ride are reported to next winter. Do you have a specific area to suggest for our next demo? We are making our plans for next year.
Thanks
 

Hawkster

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If you’re looking for reliable powerful snowbike, there’s a solution... at least 160 hp full injection...
Much better video , your starting to show what power and a one does for those that want to run at a different pace . Using a very good ski and I guess it would be up to the purchaser on what ski they want to use .
Have you noticed if the kit makes a difference in drag ? Does it take less throttle to do basic riding ?
Are you making this for other brand machines ?

The Alpha skid / Mountain Max is amazing but the front end defeats what it can do by resistance of allowing it to respond with a more subtle touch .
 

Cooksend

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We went to Revelstoke in February for demo ride. This winter with COVID situation, all other demo ride are reported to next winter. Do you have a specific area to suggest for our next demo? We are making our plans for next year.
Thanks
I spend most of my time riding in the western U.P.
 

EXO Sled

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Much better video , your starting to show what power and a one does for those that want to run at a different pace . Using a very good ski and I guess it would be up to the purchaser on what ski they want to use .
Have you noticed if the kit makes a difference in drag ? Does it take less throttle to do basic riding ?
Are you making this for other brand machines ?

The Alpha skid / Mountain Max is amazing but the front end defeats what it can do by resistance of allowing it to respond with a more subtle touch .
Thanks for your comments! This kit offer less drag than A-Arms cause the ski is just underneath the potential draging parts. Plus, the ski give good snow quality to the track!
Regarding throttle, it depend how the rider want to be aggerssive on it. Like a bycicle, a minimum track speed is needed!
For now, we can say it's only for Polaris AXYS chassis. Stay tuned!
 
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