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Discussion Starter #1
hey guys i recently purchased an '03 rmk 800 151". it's all stock except an slp intake. other guys with similar sleds love them but what do you guys think and what's the hp rating on these? i think i'll put on an slp exhaust this summer but other than that probably stock. excited to learn more about it through the forum
 

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I can't tell you a thing about your new sled, but I can offer you a sincere welcome to what I consider the best sledding sight on the net....

WELCOME! :christmas:


Duane
 

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Discussion Starter #7
yea i'm not that worried about it i actually haven't even had a chance to ride it yet but i've ridden my brother's which is basically the same and it has more than enough power for me. thanks for all the replies!
 

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What does it matter? :eek:hmy: Enjoy it!!! :thumbsup: Someone else will always have more! :wink:[/b]
now this is a challenge mike, you think we would build onw with more then the 750 HP rated r had. im thinking overhauled 502 all alum and titan parts you in a 50/50 cost build. haha
 

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id say more of the 135 range but it depends on altitude[/b]
Yeah exactly, remember you lose a lot of HP as you gain altitude. 135 at sea level, probably. I would also add, if you don't already know, that if you upgrade your exhaust on a mountain rig most people would highly recommend that you still want it to be a single and *not* twin pipes. Twin pipes kill all your low end power and completely alter your clutching. I know because I've got the twin pipes on my RMK (because I bought it that way, and it ran terribly when I got it) and I *had* twin pipes on my Vmax Mountain Max (bought it that way but switched it to stock because the clutching was a nightmare) and while you can eventually tune the piped engine really nice for a given altitude range (took me about 10 rides on the RMK), the clutching becomes much more finicky and touchy and it becomes super easy to mess up. The tuning process is even harder with Yamaha because they have few aftermarket clutching parts. There are a ton for Polaris, but it's still a real challenge getting good consistent results. Twin pipes should always give you the most top end and that's why some people prefer them.

Tuned twin pipes give a very turbo-like boost (but from the exhaust side, when tuned pipes were invented this was referred to as "reverse turbo" effect) by reflecting a perfectly timed pulse back into the cylinder just as the exhaust port is closing, thus boosting the compression. They also allow for more total air flow, but the tuning is the more important benefit, otherwise some people would still be using megaphone exhausts. This is why you MUST use premium fuel with twin pipes, because they do raise your peak RPM compression. Problem is this timing is "tuned" like a musical instrument and will only work at or near your peak RPM. At any other RPM the pipes are out of tune and do nothing for you except kill your low-end because now you have no exhaust backpressure coming in from the other cylinder and therefore much *less* compression in the non-tuned ranges (mid and low). VES engines should do a bit better, but from what I have been told, read, and personally experienced, any time you use twin pipes you can expect to lose your low end. I can say for sure that running my Honda Civic without a muffler noticeably cuts the low-end power (did that for a few months), so I think it's fair to extrapolate that if a 4 stroke car engine loses torque when it loses exhaust backpressure, the same should definitely be true for a VES 2 stroke.

So since you have no low end, you must set your engagement very very high. But it's not so easy, because since you have lost so much low-end compression, changes in altitude affect your engagement RPM more severely than with a single pipe. You'll find at higher altitudes you try to take off from a stop and the clutch is engaging too soon (too low) and the engine just can't wind up because there's not enough power to get moving. In three feet of powder, you are in big trouble at that point. On a single exhaust you would have plenty of low-end power at that RPM, though it would still be reduced. And of course, if you try to tune it for higher altitudes, then when you are riding in lower altitudes it will overrev like crazy. My riding areas don't go above 6000' and we rarely get below 3800, so in that fairly narrow range I have my rig set up really really perfect...finally...but if I we go for a real mountain climb in some other area I would probably have to take my Vmax Mountain Max because the clutching is so much more forgiving. I have taken it to 10,000 feet with good power even though it is tuned for 4500-7000'. The piped RMK would be toast probably by 7000' (tuned for 4000-6000) because it just wouldn't be able to wind-up from a stop anymore. If you never stop or if you are riding on hardpack/slush it would probably do okay. In powder I would would have to tune it for high altitude first then take it real easy on the way up.

If you really want to pay to upgrade go with a SLP mountain single exhaust or another reputable manufacturer, but for God's sake make sure to follow the NEW clutching and jetting chart that comes from the pipe maker. The worst thing you can do to your seld is an incomplete/improper mod and I've seen it time and time again. Personally I would stick with the stock exhaust unless it's dented or has a hole in it. Then make sure the clutch is set up properly for where you are going to ride following the Polaris clutching chart (if you are using the stock exhaust). Then make sure the jetting (main jet and needle position) has been boosted for the SLP intake (I have one of these too) following your Polaris jetting chart and raising it from there. You can get the rejetting instructions off the SLP website. If the stock main jet is in there now, you are running lean. Don't assume the previous owner set up the sled correctly, because so far I am 5 for 5 in buying sleds that were WAY WAY off in both clutching and jetting, sometimes simply off the chart and barely functional. Going by the proper chart is the only way to go. You can tweak from there.

Anyway, that's the short answer. Heh.
 

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Discussion Starter #10
thanks for all the info beaxch its really helpful. i looked on the slp website for rejetting instructions and it said "+2 sizes on the main jet and some may also require one step richer needle e-clip position" but how do you go about doing this? (sorry...never done it before)
 

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hey guys i recently purchased an '03 rmk 800 151". it's all stock except an slp intake. other guys with similar sleds love them but what do you guys think and what's the hp rating on these? i think i'll put on an slp exhaust this summer but other than that probably stock. excited to learn more about it through the forum[/b]
welcome to the family :)
kevin
 
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