Question; can you get away with a little less octane at higher elevation? MCXpress is showing a 250 HP upgrade for the sidewinder but recommends 98 octane RON =94 octane USA(I think this is correct). I think the highest pump fuel in town is 91 octane. The elevations I ride are 8000ft. and up. What do you think, would the 250HP kit be safe with 91 octane pump gas over 8000ft elevation?
octane vs elevation for sidewinder
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Typically, yes you can get away with a lower octane at high elevation. Turbos have limits on this concept of course....your not going be running high boost on pump gas at any elevation without major failures. i have been running my yamaha 4 stroke turbos in colorado for years on 91 with no issue. im not running quite 15, but close at 12 or 13. if you are worried and you want to be safe, you may consider getting a drum of 114 race fuel and adding a gallon or two per tank of 91 octane pump fuel. You also may want to find out if the sidewinder has "turbo" pistons in it and what the compression ratio is.
running 07 mcx apex at 12pound boost on 91 pump. I have been told that I could turn it up to 15lb for the elevation I ride. Just looking at the numbers for different kits for the sidewinder. Evolution Powersports has a 14lb 238 hp kit with 91 oct. MCXpress has a 15lb 250hp 94oct kit. looking at this. The write up says at just over 200 kpa total pressure(=15 psi turbo pressure "AT SEA LEVEL")for a lambda 0,80. I ride 8000 to10500ft. Would this give me some wiggle room on octane? Also Evo has a 16lb 258hp kit with 95oct. How much boost can I run up here with 91 octane? I want the most horse power without race gas and no problems.
You want what everyone wants. BUT it's a risk. I'm with the above who says to splash 1 gallon of 112 per tank. At 10 gallons a fill your at better than 93 octane.
Could also mix 100LL Av gas.
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Remember, it is not just compression ratio and boost that determines octane requirement. Intake temperature is a large factor as well. At higher elevations (mountain riding), the turbo is less efficient which mean hotter compressor discharge temperatures. This combined with lower ground speeds and frequent running with the intercooler completely blocked with snow - all lead to higher IATs. This can cause octane requirements to go up. Our high elevation testing should be wrapped up next week with final high elevation octane ratings.
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would be interesting to see a water to air intercooler addition to the side winder.
interesting, thanks for info Evo.
Depends on your kit, I'd install a a/f gauge to be sure that your fueling for the higher boost, my own apex, a 06 came with a probable gen 1 mcx kit, I'm told the 310hp one. meaning a ok turbo brain box, and the smaller 16t turbo. However mine has a aftermarket fuel pump and I removed the one in the tank. Now I've run 18# boost on it all day on 94 octane, no issues. I run 15# all the time. I run, at approx 6k elevation. 18# is more heat than power due to smaller turbo.
Guys I ride with run 15# on 91 pump, hell 1 guy was 89 octane lol... A bit ballsy I think. I run 94 above 91 for extra protection from detonation otherwise kit is fully intended for 91. So your fine at 15#. The mcx kits came with the head shims. The apex is a higher hp producing engine over the nytro for boost and also considered stronger, probably due to the extra cylinder.
I guess I shouldn't compare the apex to the sidewinder for boost/octane numbers. I'm not looking to turn up the apex. I'm just looking at what I would loose and what I would gain if I went from the apex to the sidewinder. So far it looks like I would loose about 40hp. That may be ok IF the sidewinder is 80 to 100lb less than the apex. haven't seen any real weights for the sidewinder yet. please, someone fill the tank on a sidewinder mtx and weigh that thing!
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It weighs 643 lbs full of fuel.
There's a pic in another thread in the yamha 4 stroke section
There's a pic in another thread in the yamha 4 stroke section
pulling a sidewinder over on hard ground was a little bit easier than my 15 viper
If you can afford a turbo then you can afford some 100 ll. I mix 50/50 110 and 91 and have run up to 18 lbs of boost without an issue. Look at your worst case scenario and decide what you can afford more. A little more money per tank or a major engine failure. I know which one I will always choose!!!!
Its not about cost its about convenience for me. Had a sled that required mix of race gas and it was a pain in the butt. Did not like having a drum of race gas stored in the garage, never knew if station was going to have race gas in stock and out of town trips were a concern. Then I went to the turbo apex, pull up to any gas station, fill it with 91oct and go ride. I will go with sidewinder kit that is safe with 91 or I will stay with the apex. looking at power to weight ratio the sidewinder falls a little short of the apex with the 225hp kit on the sidewinder.
ID wait until mid winter when guys have been out for months and also tried some of those ecu updates from aftermarket companies, right now it's a lot of speculation, I think mcx claimed around 240hp on 91 pump gas... With a aftermarket muffler...? But who knows.... Then I'd be concerned of size of turbo to push that 240 hp, factory one is small for no lag at like 180 or 190 hp. Which I'd bet is fairly out of efficiency range going beyond in hp. Might just be a heat pump.
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