Low compression doesn't just give up power (unless your boosted of course), it gives up efficiency! They way it has to be when air cooled though... along with loser piston to wall clearances...

When I installed the 114hp larger cylinders / forged pistons on my 912, the comp went up to 11:1. Runs happy on car gas and burns ~3.75 gph (110-115mph indicated cruise). It was 4-4.25 gph before the upgrades)

Of course I have a coolant system to keep in tact, but they say you can limp home on one of these if you lose it with the cylinder fins alone... hope to NOT find out

Pretty good fuel burn. My 110 hp O-200 burns 4.29 gph.

maules.com wrote:For interest and comparison re Franklin engines

350 cu inch, 6 cyl, 10.5:1 comp, 100/130 fuel, 2800rpm, 28BTC, weight inc mags carb 339lbs, 220hp
350 cu inch, 6 cyl, 10.5:1 comp, 100/130 fuel, 3200rpm, 28BTC, weight inc mags carb 304lbs, 230hp

What's the difference between these two engines? 400 rpm to get another 10 hp seems a bit much, but 25lbs. less weight is interesting...

In a C90 or O-200 with stock 7.00:1 compression, installing 9.5:1 pistons will give you a 9.76% increase in power without changing timing, jetting, or venturi size. For an O-200, that gives sea level 110 hp at rated 2750 rpm. The 9.5's will run fine on 93 octane mogas at 28°BTDC.

Hal Stockman (Mr. Big Bore) LOWERED my 912s compression while increasing the displacement. I burn REGULAR mo gas, with ethanol when "on the road", regular pure no gas at home, when above 2500' field elevation ( always in my area, unless spelunking). Yesterday, at 8 K asl, 80 mph indicated, 3.9 GPH. FWIW. Indicated airspeed without stating the elevation is incomplete info

JimC wrote:In a C90 or O-200 with stock 7.00:1 compression, installing 9.5:1 pistons will give you a 9.76% increase in power without changing timing, jetting, or venturi size. For an O-200, that gives sea level 110 hp at rated 2750 rpm. The 9.5's will run fine on 93 octane mogas at 28°BTDC.

Does this 9.76% improvement in HP make the exact same 9.76% improvement in torque, or is there a larger/smaller effect on torque from the compression ratio?

Horsepower is just great, but as we have all been taught over and over... thrust is what actually moves the airplane.

It has the same effect on torque. As you know, the mathematical relationship between horsepower, rpm, and torque is explicit and linear. If you know any two of the three, you know the third. The 9.76% increase is just the thermodynamic effect due to the compression change from 7 to 9.5. The actual increase can be less than that, but cannot be more.

EZFlap wrote:

JimC wrote:In a C90 or O-200 with stock 7.00:1 compression, installing 9.5:1 pistons will give you a 9.76% increase in power without changing timing, jetting, or venturi size. For an O-200, that gives sea level 110 hp at rated 2750 rpm. The 9.5's will run fine on 93 octane mogas at 28°BTDC.

Does this 9.76% improvement in HP make the exact same 9.76% improvement in torque, or is there a larger/smaller effect on torque from the compression ratio?

Horsepower is just great, but as we have all been taught over and over... thrust is what actually moves the airplane.

True, and thrust (force. created by the engine doing work on the air) is generated by horsepower (power. Work done over a period of time). There's another thread on here about that.

HP=Torque*rpm/5252

So, as you can see, for a given rpm, if you increase one by ten percent, you increase the other by ten percent.

JimC wrote:HP=Torque*rpm/5252

So, as you can see, for a given rpm, if you increase one by ten percent, you increase the other by ten percent.

True!

Automotive electronic ignitions prevent detonation that could be experienced in low grade fuels by incorporating a knock sensor that alerts the ECU to delay the timing map. They actually do it for individual cylinders; you can have 15 to 20º difference between any one cylinder. If aircraft could get that kind of technology (auto manufacturers have been doing this since the 80's), it would simplify the search for a 100LL replacement.

Now, for some REAL education:

https://www.youtube.com/watch?v=Ac7G7xOG2Ag

With the electronic ignitions, how do you prop non-electric aircraft?

JimC wrote:With the electronic ignitions, how do you prop non-electric aircraft?

One blade at a time...

Kidding. The electronic Ignition systems I'm aware of require battery power. I do believe some still allow for hand proping. Plenty of people compromise by running an electric system, but ditch the starter and flywheel to save weight.

Can't see using an ignition that requires an electrical system to run it.

JimC wrote:Can't see using an ignition that requires an electrical system to run it.

Essentially you have two independent/redundant electrical systems. Also, some setups have electronic ignition on one side and a traditional magneto on the other.

Certainly not for everyone, but the fuel savings and ability to run various fuel types can realize thousands of $$ in fuel cost avoidance. Not to mention some sexy gains in HP.

Sounds like weight to me. I prefer armstrong starter on aircraft certified non-electric so I don't have to have transponder or ADS-B.

Fuel is heavy! Think of how much less you'd have to carry if you could cut your fuel burn down by 20-30%.

And for what it's worth, I understand where you come from; less is more!I do most of my flying in a friend's C-90 powered BC12D, no electric.

Sent from my SM-N910V using Tapatalk

whee wrote:I thought about that for a half second Marty. 220 Franklin in an experimental set up to run E85, but decided against it.

Awesome stuff for power. Made 570whp out of a 2.0L with 35psi of boost. Can run more timing (can exceed MBT if not careful) And EGT's were 150 deg+ lower than gasoline (lower hp on gas and still that much cooler). But the ~30% more fuel quantity required would sure hurt range in an airplane