SrTelemaster150

OK 1st of all, if you fly the modified engine @ the same power output of the stock FA450R3, it will in all likelyhood under less stress than the stock engine.

The CDI is free power, it's better than free as it also saves you money. It can save you a LOT if you can mix your own methanol/oil mix @ 10:1 or so.

The power is also a more dependable, less volitile power as the ignition timing will never change W/ambient temperature, nitro content, A/F mixture, etc.

The CDI makes more power by precisely timing the spark event & burning the fuel more effecienty.

THIS IS A NO BRAINER! Anyone that runs & intends to continue running a large displacement 4s should convert to CDI. There's just no arguable reason not to & many reasons that you should.

So, let's say my high compression idea pans out.
Higher compression, as long as you stay within certain parameters, is also better than free because it will be more fuel effecient @ low to moderate throttle settings. It will use slightly more fuel @ WOT because it will be (effeciently) pulling more air & with it more fuel through the engine.

Now, you are making more power because 1) the piston is expelling more of the spent exhuast simply because the piston is leaving less cc of unocupied space in the combustion chamber (CC) 2) as the piston starts it's downstroke & is pulling on less unocupied space in the CC, therefore it will start inducting air sooner 3) as the intake charge is being compressed on the upstroke it is squeezed in to a smaller unocupied space. The higher CC pressure will increase the force that the expanding gases exert downward. That's translated to more toque @ the prop shaft.

You will not be attempting to increase the operating RPM range as you would W/cams & significant induction modification. So far you have only Made the engine more effecient W/the air & fuel that it cycles through it. If you prop the engine for the higher TQ it will run as long as the stock engine even @ WOT.

NOW, If you want to go a step further: Adding a bigger carb is not one of the freebes, it will only produce more power by allowing more air/fuel to go through the engine.

The FA180HC CDI engine really woke up when the 12mm big bore caruretor was instaled on a ported intake manifold. To make the ported manifold I took an old 150 manifold & bored the updraft section to the 12mm bore of the carb. I then drilled the horizontal section out to the larger 180 EX port diameter. The trasition from the 12mm section & the smaller section was blended smooth for maximum airflow through the 90° bend. The engine gained 400 RPM jumping to 8450 RPM W/an 18x8 Dynathrust prop.

The stock FS450R3 has a 9mm carburetor. This is sized for the 150 based bore as only 1 cylinder @ a time is pulling on the intake & @ low RPM there is more time between the intake pulses. The carb is sized to make the GI engine more well behaved @ lower RPM levels. It also restrains the engine @ WOT, high load, high RPM operation. The enhance breathing of the higher CR will allow the engine to oerate @ a low rpm level W/a slightly larger carb.

The good news is, there are 3 larger carburetors to work with to tune the modified engine for maximum all around performance..

The 450R3 carb is 9mm bore. All of the big block Saito singes use larger carbs.

FA150 uses a 10mm carb
FA180/220 use an 11mm carb
FA220 has an optional 12mm big bore carb

So anyway, we have increased the power by 25% & decreased our fuel usage by 50% by doubling our fuel economy. We have brought the power level up to point where the engine can still be run @ WOT for a good percentage of the time W/O reducing engine life.

Well, W/a methanol engine you can significantly bost power by tipping the old nitro bootle a little. When I bolted the BB carb to the 180HC CDI it was impressive, a 400 RPM boost. When I upped the nitro to 30%? Holy Mother of God! Did that sucker beller nice. When you get above 8400 RPM swinging an 18x8 prop, adding another 400 RPM takes some serious snot! It did it though, 8850 RPM, thus detroying the myth that nitro doesn't boost HP W/CDI. Too be honest though, the reduced 8% oil content helped a lot. Oil doesn't make power & there's no need for 16% oil in a CDI methaniol 4s in a fixed wing aircraft.

Here cames the reality check. Now that we are hitting the nitro, we are paying for it. The nitro require a higher volume than methanol & if you ran the engine W/30%nitro 8%lube @ WOT for long periods, it would most likely reduce engeine life, perhaps significantly.

The nice thing about nitro, especially if you DON"T NEED IT, is that it is HP in a bottle. You can make as much as what pleases you or what the engine will take. The later scenerio is the not so nice thing about pusing an engine beyond its limits.