Posts
18
Joined
8/23/2015
Location
Chesterfield, MA
US
Edited Date/Time
9/25/2015 7:31pm
Hey everyone, so I just bought a 2014 Ktm 250sx. I've been doing a lot of research on here and other places on the Internet on whether to run pump, AV, or race gas. I thought I had made my mind up to run AV gas until I went to my local shop today. They said to just run pump gas. So what do you guys think? Also I've been running 32:1 ratio in my yz125. Would that be fine in my new bike?
Thanks!
Thanks!
Paw Paw
The Shop
The basic contention is that AV gas isn't designed for high rpms. Neither is pump piss. A justification can obviously be made in favor of race fuels for this (and other points), but the swill from the pump is designed for anything but performance.
If the engine can't utilize 100+ there's no point in wasting $. Not entirely true.
-Unlike pump piss, Av gas has far less enviro-nazi additives and burns far cleaner. This makes jetting easier and more consistent. The lack of so many ridiculous blends assists in that too.
-While an engine may not require 100 octane, if it's on the edge of detonation with PP (pump piss), then the additional octane will provide a safety buffer, particularly if there's a higher load (mud, sand, etc), or as the engine wears in.
-Without the additives, there is a more complete burn, at least from the standpoint of not leaving drool in the silencer and carbon on the piston and power valves.
In my personal experience, every bike I've run 100LL in has either run better (RM85's, YZ85's, YZ125, KX125, CR250, YZ250, CRF250R, CRF450R, and more), or has had no noticeable effect (XR50, TTR90, TTR125, WR250F, Briggs and Stratton).
To JH911's credit, his statement of "Octane has nothing to do with how much HP it will make. It is simply a fuels resistance to detonation and or pre ignition. So more is not always better." is completely correct. So while my TTR125 and lawn mower might smell better with AV gas, they don't perform better. Actually because the compression ratio is so low on them, 87 octane will likely produce more power than 100 octane non-oxygenated fuel will.
I have heard statements about AV gas most of my life.
What I have never heard from anyone is a scientifically informative explanation of how the chemical composition of AV gas is significantly different from automotive fuel including how and why those differences will cause negative effects on the performance or longevity of a 2 stroke racing motorcycle engine.
AV gas is superior to pump fuel in real world use in a 2 stroke motocross bike. It is more consistent, easier to jet and less prone to detonation. As for which fuel makes more horsepower, who cares. Run the fuel that makes the bike more reliable and consistent.
True racing gasoline is a huge improvement over both of the other options in both consistency and horsepower.
The avgas critics simply don't know what they are talking about.
However, I am going to switch to AV gas or straight race gas soon, for the simple fact that it is consistent year round. I'm planning on riding indoors this winter, and I don't want to run winter blend. Not to mention, I don't ride a huge amount maybe once a week, and race gas smells amazing.
Moving on to AV Gas. I threw out something I was told by an old aircraft pilot and a current commercial airline pilot, both expressing opinions why they wouldn't use AV gas instead, just using a quality race fuel. I guess like myself they believe in using things that were designed and engineered for your specific application. I have also been told by a former aircraft mechanic aside from burn speed; AV gas was designed for high altitude and low compression engines. Which I found interesting being as it is not oxygenated. If your going to cut it then what's the difference?? A couple $$? Run some race gas. AV gas has a ton of great properties. Consistent, stable, won't go bad for a long time, contains lead (although I have seen plugs lead foul). However, once again the point was to use what is engineered and designed for your application. As far as AV gas vs pump specifically, I guess it depends on where you live and where you get your gas. I guess I take for granted we have a local bulk plant/station that for over 40 years has sold nothing but quality ethanol free gas that is consistent and blends don't change with seasons because they're not a franchise station that has that dictated for them. They also sell race gas at the pump that's not much more than AV. I prefer Renegade or VP myself, but again to each their own.
1. Price. I just picked some up today for 4.50 a gallon, that's a pretty economical fuel for guys like me on a budget.
2. Availability. I pass by a small airport very often so it is easier for me to get than race gas, which I would have to get through a shop or dealer that i don't frequent as often.
As for the car oil, I already said I no longer run it due to the wet clutch found in all our bikes. I used to run a Castrol motorcycle oil but switched to Rotella after reading around online. For those who like to stretch their oil changes out then they might notice some issues with car oil, but for me I never had a problem since I changed it so frequently. I probably wouldn't recomend running car oil to anyone, but I honestly never had any problems for all the years I used it so I don't know how long you would have to push it to see adverse results.
I don't think anyone is trying to berate your points because they are valid and you have good info, I just don't know how far the theory really extends into practice on stock machines, especially two strokes. For me it just doesn't make sense to run expensive oil since I change it so often, and it doesn't make sense for me to use race gas since I'm not looking for a boost in performance. For guys who want top performance and longer oil life, by all means run the application specific stuff, but I don't think that has to be the only option for everyone.
Do you know the typical running oil temperature in a MX bike? Do you know the oil temp in a typical car engine, or performance car engine? Wanna talk about RPM's? Let's watch this consumer car turn 10k plus...
https://m.youtube.com/watch?feature=fvwrel&v=l15l3nTLmhE
And I doubt he's running motorcycle oil. Think about all of the makers of "motorcycle oil", where do they get their raw materials from? They all start with the same product.
You put so much faith into the words "specially formulated". It is important to remember that these "special formulations" were created by men no smarter than you or I.
Having said that, there are some hot rod boats that they recommend using regular gas and not even premium. They are designed to run on the lower octane. Explained this way, the higher octane does burn slower to prevent knocking but it also burns at a higher temp and folks have been known to melt pistons. But a boat motor is constantly under load.
So when they say the gas or oil is all the same base, well all the beer is made with hops right?
And yes the folks that formulate the stuff are smarter than us, maybe not in life but for sure in their craft.
Lastly, as far as car oil goes. I firmly believe that they sell so much of the shit that they maximize their profits not by making the best oil, but by installing the minimal amount of the good stuff just to eeck past the government/industry standards to get their rating. Because yes the additives play a huge roll.
From Cessna Pilots Assn. aritcle. Many years ago, used to fly a 1976 182P
"1956 through 1976 model year Cessna 182 Skylanes can receive STC approval to operate on auto gas. The makeup of auto gas coupled with the Cessna 182 Skylane's induction system produce a couple of interesting operating characteristics. First of all because auto fuel vaporizes more readily than aviation gas it is possible to develop carburetor ice at higher outside air temperatures on auto gas than on aviation gasoline. The amount of ice that is produced remains the same but pilots will notice carburetor icing occurring at higher air temperatures on auto gas than they are used to experiencing with aviation fuel.
TM
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