The International Cessna^® 170 Association

Just got another call from a Member who wanted my opinion on Power-Flow exhaust systems. (What? ME? Have an opinion? What kinda nuts are joining up here anyway?)

Dare I re-open this subject? I think I have been on record for some time to say that in order for a magic exhaust system to work, there must be a proportional increase in fuel consumption and/or temperature. This is contrary to their marketing statements that claim reductions in fuel consumption and heat.
Apparently I'm not the only nut on the wheel. I sent him to Sacramento Sky Ranch for another opinion.
http://www.sacskyranch.com/estimate_power.htm

Not sure I agree with there analysis on this one. If everything else about the engine remains the same, then what they state would be correct. But by changing the exhaust, you now modified the engine to increase volumetric efficiency which would reduce the amount of power to force the exhaust gases out of the cylinder. Having said that, I think the claim of a 25% increase is a little extreme.

25% might be like performance claims I've seen in the high-performance computing industry. Engineers, being inherent optimists, come up with a number. The marketing folks like the sound of it, and put it out there. The smarter customers recognize it for what it is -- the number the engineers absolutely guarantee the product will not exceed. Nothing more.

For instance, if you claimed a 42" pitch propeller might pull the airplane through the air 42" per revolution, you'd be quoting a number engineers use, but it's really an upper bound on the actual performance. Other (lower) upper bounds could be found if the marketing folks happened to ask the engineers for them -- but why would they?

Best Regards,

John

Simply put, if an exhaust system can deliver more static RPM using the same prop or prop setting, under the same atmospheric conditions, then you're making more power.
Strangely enough, I've never found anyone with a custom exhaust system who has made this comparison.

When I look at aircraft motors like ours I can't help but think that the intake system is where the restrictions are. If that could be opened up without sacrificing reliability I bet there's a few more foot pounds of torque to be had out of our motors at 2700rpm.

The problem with increasing torque in these engines is that their reliability will suffer. You can't increase hp output without affecting vibration and stress on all the gears, counterweights, conn-rods, piston/rings, valve operating temps and stresses, prop, prop flange, etc. On top of that, there comes with increased hp output increased heat. This engine cannot increase it's cooling fin area, nor it's surface area of the sump (oil cooling) without really big engineering changes. Continental has already done this work...it's called the IO-360 engine, which has added 60 cu. in's and the other necessary mods to accomodate that increased torque/hp/heat.
You just can't change one thing without affecting all the rest and/or reliability.

I agree George, and it's all just a moot point anyway, it's certified as is and nobody is going to spend the money or time to make it better when there are more powerful platforms available now to start with (ie if I were making a motor for an experimental plane).

gahorn wrote:The problem with increasing torque in these engines is that their reliability will suffer. You can't increase hp output without affecting vibration and stress on all the gears, counterweights, conn-rods, piston/rings, valve operating temps and stresses, prop, prop flange, etc. On top of that, there comes with increased hp output increased heat. This engine cannot increase it's cooling fin area, nor it's surface area of the sump (oil cooling) without really big engineering changes. Continental has already done this work...it's called the IO-360 engine, which has added 60 cu. in's and the other necessary mods to accomodate that increased torque/hp/heat.
You just can't change one thing without affecting all the rest and/or reliability.

George, you forgetting about the GO-300 which puts out 175hp with the very same cylinders we use in our O-300s. There are ways of increasing HP without increasing heat.

lowNslow wrote: George, you forgetting about the GO-300 which puts out 175hp with the very same cylinders we use in our O-300s. There are ways of increasing HP without increasing heat.

That's not correct, Karl. The GO-300 (discontinued dismal engine that it was) suffered from greatly increased heat and other stresses. They were NOT the "very same cylinders".... they actually had to redesign the cylinders (which although they could be installed on O-200/300 engines the original O200/300 cylinders were NOT applicable to the GO-300) and they had to design a gearbox to handle the increased RPM, and they had to install bigger gas tanks to handle the increased fuel burn, and they had to redesign/install an oil cooler system to get rid of all that extra heat! They also designed a different cowl and cooling baffle system and evenually admitted they also had to install cowl flaps as well in the final version of the C-175, to handle the additonal heat.

gahorn wrote:They were NOT the "very same cylinders".... they actually had to redesign the cylinders (which although they could be installed on O-200/300 engines the original O200/300 cylinders were NOT applicable to the GO-300) and they had to design a gearbox to handle the increased RPM, and they had to install bigger gas tanks to handle the increased fuel burn, and they had to redesign/install an oil cooler system to get rid of all that extra heat! They also designed a different cowl and cooling baffle system and evenually admitted they also had to install cowl flaps as well in the final version of the C-175, to handle the additonal heat.

I should have been clearer in by response. Obviously the GO-300 would put out more heat, I was refering to the cylinders, which are the same, at least the present day versions. The problems the GO-300 cylinders had were also problems for the O-200 and the O-300. The GO-300 engine was actually not such a bad engine if flown correctly. Had a great conversation with the airport manager in Oroville on the way to the convention who had a very nice 175. He has had quite a bit of experience with this engine and he gave me a great tutorial on how to fly it "by the book" which is different then the way most of us fly our direct drive engines. The big problem with geared engines is low TBOs.

But to get back to the original thread, you CAN increase horsepower without additional heat and fuel flow.

lowNslow wrote:But to get back to the original thread, you CAN increase horsepower without additional heat and fuel flow.

How? I can see where bumping up the compression will net you some more power without an increase in fuel flow, but there's still going to be more heat.

Just look at modern auto engines. They put out the same hp as their 30 year old predecessors with almost half the fuel flow. This has been done with computer controlled ignition and fuel injection, 4 valves per cylinder, improved exhaust porting, etc. etc.

Right but that would be designing a new engine, Honda was working on something I thought I heard, if they get something certified I'm sure it would blow the doors of anything Lyc. or Cont. has made. We however, are stuck with 60 year old engine designs.

Jr.CubBuilder wrote:]We however, are stuck with 60 year old engine designs.

I am afraid so, unless we want to upgrade when some of these newly promised engines come out.

and you'll have to STC approval from the feds.................
Now that I think about it, can you just modify a certified aircraft and have it registered as experimental?