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Discussion Starter #1 (Edited)
Hi guys. I'm building a snow bike out of a raptor and trying to decide between 5050 and web 4. Snowbikes are run wide open at 10000 feet all day long. It's like climbing a never ending sand Hill. The drone on 450 mx bikes is obnoxious and many wear ear plugs. My build will be 14:1 corrected comp or higher, Pump gas, no air box or filter (just a screen pod to keep pine cones out) and the lightest pipe I can find under 96db. It's already a heavy pig and duals will make it unbearably heavy in my mind... All logic says the less overlap on the 5050 will work better with a less than perfect exhaust flow but on all the snowbikes I've built the peak top end number always wins and they have to stay in the top end all day. Low end torque is useless unless you're going down hill you need to stay on the hp bubble. Also I'm afraid to go with any bigger cam because of excess wear on the valve train. It needs to be reliable. The good news is at 10k my 70hp engine is only going to have 50hp so the bottom end should stay together just fine.
 

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Call Daniel at +1 (951) 743-6328 (Cuervo Racing) and talk to him about what you’re wanting to do. If you want to move the power to higher rpm, might look toward the 5150 or even 5250 cam. Still only .550 lift I believe. I’m just not sure how either would perform on a small motor with small valves. It’s very possible to turn a bunch of rpm reliably.
As far as exhaust goes, it’s hard to keep under 96db through a single that still performs. If you aren’t shy of spending some $$, you could build your own duals setup. Titanium tubing and carbon mufflers do exist.
 

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How can you run 14.1 or higher compression on pump gas?
Elevation and valve overlap.
The fuel we run in 17:1 or higher drag engines is less octane rating than premium pump gas.
 
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I know elavation effects it/less oxygen, but the a/f still has to be correct, so I don't quite understand why pump gas(that's 87-93 octane east coast) doesn't detonate before ignition.
Or if valve overlap is so great, intake and exhaust momentarily are open together, effectively dropping compression, but that sounds like valve float.
Add that to below freezing temps, high load on the engine, and constant high rpm use; how long does something like that last?
I've been all over the country and driven over the Rockies, and know what high altitude feels like, but 4k' would be about the max out here, with most of my riding between 1k'-2k'.
I'm not familiar with high altitude tuning.
 

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I know elavation effects it/less oxygen, but the a/f still has to be correct, so I don't quite understand why pump gas(that's 87-93 octane east coast) doesn't detonate before ignition.
Or if valve overlap is so great, intake and exhaust momentarily are open together, effectively dropping compression, but that sounds like valve float.
Add that to below freezing temps, high load on the engine, and constant high rpm use; how long does something like that last?
I've been all over the country and driven over the Rockies, and know what high altitude feels like, but 4k' would be about the max out here, with most of my riding between 1k'-2k'.
I'm not familiar with high altitude tuning.
Im not going to pretend to understand it all either, but it is a thing for sure. A lot of the 450 based stuff is already over 13:1 factory and runs pump gas. Our 900+cc engines with big strokes and a bunch of dome run mr12 fuel which is only 93(r+m)/2 without detonation at sea level.

i would think elevation and cam have a much larger effect than ambient temperature. The more places I go race and the more times Im on the dyno, I see the effects of pressure and humidity.

Overlapping valves are still under control, floating valves are not.
 

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Discussion Starter #7
It has nothing to do with a/f ratio it stays the same everywhere. There is lower starting air pressure so less cylinder pressure when the flame ignites. We need to run over 5 pounds of boost to get the same pressure as sea level. Our gas pumps don't even sell premium 91 (highest is 87) and 85 is the regular octane. My 2 strokes tuned for pump fuel at 10k are running rediculous high comp. Sometimes when I'm loading them on the trailer at my house at lower elevation and below zero temps I'm getting close to sea level air density because of the cold. I have to use the choke to shut them down because they are running like diesel firing from compression only. The kill switch does nothing.
 

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It has nothing to do with a/f ratio it stays the same everywhere. There is lower starting air pressure so less cylinder pressure when the flame ignites. We need to run over 5 pounds of boost to get the same pressure as sea level. Our gas pumps don't even sell premium 91 (highest is 87) and 85 is the regular octane. My 2 strokes tuned for pump fuel at 10k are running rediculous high comp. Sometimes when I'm loading them on the trailer at my house at lower elevation and below zero temps I'm getting close to sea level air density because of the cold. I have to use the choke to shut them down because they are running like diesel firing from compression only. The kill switch does nothing.
I’ve seen similar happen at the track. Guys grab the brake and shift up real fast.
Saw one where he had to rip the filters off and cover the carbs to choke it off.
 

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The Raptor has a large piston/chamber volume and can't tolerate higher compression like a 450 can on pump gas. As an example my CR250R runs a 13.5-1 on 93 E free pump gas, on my Raptor 12-1 is the max I can run and it has a large duration/overlap cam. Extended high rpm's wears/hurts motors, that's why pro MX riders have very frequent rebuilds.
 

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Discussion Starter #11
I'm hoping I won't have to rev it as much all the time because the torque should be adequate to keep up with a 450 in the lower revs. Rebuilds on snow bikes are an annual thing for me.
 

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Discussion Starter #12
So Sunday should be the maiden voyage of my raptor snowbike. I'll post some pics when I get it out of the garage. Right now the motor is bone stock with a full gytr with quiet core insert. it has a totally open intake just a 3"x20" rolled screen pod to keep the pine cones out. No tuner yet so it might be lean with the intake. Will this setup even have a chance to hit 50hp? My goal for the next few weeks is to leave it stock to see how well it starts in zero degrees outside overnight. Then I'm going to contact quervo and lighten my wallet.
Last question I had is between a 5050 vs web4 which one might start easier in cold? 5050 will probably crank slower but less overlap might flow/atomize better at cranking speed? Or web4 might crank faster and sometimes that's all that matters on the 450mx bikes... would a manual decomp be recommended?
I have the feeling I'll be buying and testing BOTH cams before the session is over.
 

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Where are you running this at?
 

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Discussion Starter #14
Altitude is 10000 feet in wyoming. I know it won't be 50hp now at that altitude not even close but just comparing to a 55hp 450 mx bike that's the gold standard of snow biking and they usually only have mid to upper 30s for torque. End goal is a 70hp build that would have 50hp at 10k. And still start in the cold and be under 100db and close to 300 pounds. Pretty sure the weight will be over budget. The engine alone is 20 pounds heavier than my 450 but more power can some times be worth more weight. Time will tell...
 

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Discussion Starter #18
That thing is awesome
Did it live up to your expectations?
So far yes. The engine starts really well (most 450s don't). I won't know more until my first test ride tomorrow. Confidence is high though the key to a good snow bike is in the frame geometry and I built this one a notch better than my previous 4 custom bikes. The normal conversion kit snow bikes have the track mounted a good six inches behind the motor and way behind the rider/center of gravity. I got the track paddles on this build within a 1/4"of the engine block and the footpegs are in a sweet spot. Even the fat stock seat seems like it will work well sitting or standing. I'm going to try to weigh it tonight, cringe...I still need to figure out how to put the fuel pump inside a 6 gallon marine tank. And it will get a full plastic wrap around the engine for deep days the snow cools the engines too much from direct contact.
 
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