ORIGINAL: jeffie8696
I have found that the key to reliable performance is moderation[sm=49_49.gif]. I forgot to mention that I did do some polishing inside the crankshaft, not grinding just polishing. The only mods to the case was to take away the blockages left over from the machining process and blending the transition to the ports, the ports themselves were only given a mild polish without altering their shape or volume. The port opening in the crank was left as is with just a very minor radius to the inside of the port. I did a very small amount of work and feel the results were spectacular. I have a few more racer tricks up my sleeve, speaking of sleeves
I did not touch the liner At All! I was much too worried about peeling the coating and ruining a great running engine. 11,700 on a MA 11X6 prop is worth 5.72 lbs thrust on my static thrust computer, that is compared to the 5.32 the LA made. The results were more visible with the bigger prop. I also tried a 10X6 MA and got only .22 lbs higher thrust over the OS. I think these engines are both made to take advantage of the torque and therefore swinging a big prop they show a lot more power than trying to spin a smaller one at higher revs. The intake can only draw in so much air and I am sure both these engines use the same carb as a similar .40 size engine. (but there are ways around that too, I will keep you posted
) Let me reaffirm! I am not Bashing OS! I think if the same mods were made to my LA the results would be similar! I just needed a top quality benchmark to compare my mods to.
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Props are just like tires on a race car. You choose the tire according to the track and the type of racing to be done, you don't select just one tire and say that that tire is better than all others.
In fun-flying some years ago, when the trend was to go large on the prop, a small group of guys discovered that the plain bearing .40ish sized engines actually did better dead lifting their light models when utilizing a 10x5 prop in our type of competition fun flying. Change the events just a little bit and you were off trying to find the best compromise prop. Never did we decide than running more prop load than that of a 10x6 was better. It always led to overheating in events such as the most loops. Some clubs even adopted a rule of once you chose a prop, you had to stick with it through all of the different events.
The point of all of this is that yes, sometimes larger props are better for some events, but sometimes they are not. I see no advantage to always lugging down a PB .40, when most of the time these engines performed much better when lightly loaded.
Ed Cregger