ORIGINAL: jester_s1
Wow, what a conspiracy theory! LHS's are pushing higher nitro fuel that people don't need in order to boost their profits. That extra $3 a gallon must be a really big deal!
The truth is that the fuel you have is good stuff and the hobby shop did you right. Your engine will run fine on lower nitro if you want to save a few dollars though, and you probably won't notice the difference in horsepower on trainers and most sport planes.
There was an article a couple of years ago in one of the magazine that went into the specifics and math of all of this...
The bottom line is that medium engines up BENEFIT from both a LOWER OIL and LOWER NITRO content.... ( assuming you do not live at a high altitude where the extra Nitro helps ) than what is commonly espoused.
e.g. 15% oil and 5% Nitro is great for a .90+ sized two stroker...
While for smaller say sub .32 sized engines higher oil and 15%+ nitro is very beneficial for both cooling and power.
The article talked about how as you go up in displacement, the effective area that needs oiling does not rise proportionally, nor do the cooling needs...
The lower oil content acts to provide more "useful" fuel to the engine increasing power.
15% Nitro and 18% oil is merely a median figure meant to cover the greatest range of engines... 2 strokers through four strokers...
Since it is so often touted, everyone seems to have adopted this as gospel for ALL engines....
That article made me a convert... I now run 5% nitro on all of my .60's and above without a single problem.
At a LHS I saw 15% for $23.00/gallon and 5% for 15.00/gallon so the difference is substantial.