[RVbySDI]

Ok, this question has been nagging at me for quite some time now. I have read all the threads I can concerning engines as I have not yet made up my mind concerning what I wish to do in that part of building this airplane. I have heard a great deal of discussion on smaller engines v larger engines and I would like some clarification from the mechanical engineers, the chemical engineers, the train engineers and the general "I think I am" engineers out there.

There is a great deal of discussion about whether to run a high horsepower engine at a lower RPM in order to conserver fuel and decrease wear and tear on the engine. Some out there are in favor of this over running a lower HP engine wide open. Those in this camp believe it is better to run an engine at higher RPM's because it is built to run "at a certain speed". This "certain speed" is supposedly around 75% of max HP and will gain its best efficiency at this rate.

In the ongoing debate over large vs. small displacement engines there is much talk about pumping losses. Those in the camp of running a smaller displacement engine at higher RPM's uses this argument of pumping losses to support their stance.

So after all of this here is my question. I understand this principle of pumping losses so I would like to ask that any answers to my question would be specific in nature and not generalizations. I would like to know if anyone knows the specific delta difference in pumping losses between the 320 engine vs the 360 engine. Are these pumping losses so great that a difference in displacement of 40 ci will be enough to have a drastic enough pumping loss to offset running the 360 at slower RPM's for efficency over the 320?

So as an example, if one were to run an O-360 engine at 55% of max RPM and compare it to an O-320 engine running at 75% of max RPM what would be the difference in pumping losses for the two engines. Would the pumping loss in the O-360 be enough to offset any gains in running the larger engine at a slower RPM?

I would very much like to hear from the experts on this issue as it seems to me that the size difference in these two engines would not be great enough to see a drastic difference in efficiencies due to these pumping losses. my thoughts are that if I am comparing an O-320 with an IO-740 then perhaps this pumping loss issue would have merit. If I am wrong then I ask to be enlightened. If my supposition is correct I would like to have some specific information to support this supposition.

So please give me some numbers to chew on!

 

[osxuser]

The Angle Valve 360 series is more efficient than the Parallel valve on the top end, on the lower end it's about the same as the Parallel valve.

I don't know much about effciency other than that. I do know however that Lycoming suggests that for best life, the engine should be run at lower power settings most of the time. Therefore, running an O-320 hard will shorten it's life. At 75% power the O-320 will put out 120HP, the O-360 will be at 66.67% HP and a IO-360 (Angle Valve) would be at 60% power.

This would lead to longer engine life according to Lycoming. Fuel effciency would be higher with the IO-360 assuming you don't have a problem running LOP, which you wouldn't be able to do at 75% with the O-320 (Or even with an IO-320).

 

[David-aviator]

Steve,

I've never heard the term pumping loss, but I can tell you about running at less than 75%.

A first run 0360A4M I once owned had its oil changed every 25 hours, was flown at 2200 rpm most of its life and otherwise pampered like a baby. When it was overhauled it at TBO, the crank was in new limits, the valves were in very good shape and the cam had some slight wear. I did install new cylinders and pistons, but the overhaul guy said the original ones could have been cleaned up and run some more. In fact I sold the old cylinders to an overhaul shop and they probably are running today.

I wasted some money on that overhaul.

.....standing by here to learn about pumping loss.

 

[videobobk]

Pumping loss

Pumping loss stems from the fact that almost all gasoline engines have a throttle that restricts incoming air from going directly into the cylinder, at least when not wide open. When wide open, the engine only has to overcome the friction losses of the induction system; air and fuel passing through a filter and some tubes. When the throttle is partially closed, the manifold pressure drops, and the drop in pressure in effect is working against the piston on the intake stroke. The engine is working to produce a certain amount of vacuum.

With a higher hp engine, in general you would run with the throttle closed off more to lower the hp. That, coupled with either larger diameter pistons or longer stroke, equates to more power absorbed in pumping the air/fuel mixture. Diesel engines have no air throttle and do not suffer these losses. I understand some BMW engines also eliminate this with valve timing that allows air to pass out of an open valve on compression at anything less than full throttle. I understand they have 15-20% better economy at low hp. Neat idea, but hardly new. Old "hit and miss" engines of the late 19th/early 20th century used this to regulate engine speed.

No, I'm not an engineer, but somewhat of a historian. I also was senior tech writer for Cummins Engine Co. Hope the explanation helps.

Bob Kelly

 

[hevansrv7a]

Managing pumping losses - an idea

The pumping loss is the direct result of partially closed throttle. With a CS prop, can't you slow it down and open the throttle and thus eliminate the pumping loss? Wouldn't this also save wear with fewer piston miles? Of course, those fewer miles will be at higher pressures which means more ring-cylinder friction. I know this raises the spectre of "over-square" operation, but hasn't that been discredited as long as you are under 75%? Experts, please feel free to critique this.

 

[David-aviator]

Pumping loss stems from the fact that almost all gasoline engines have a throttle that restricts incoming air from going directly into the cylinder, at least when not wide open. When wide open, the engine only has to overcome the friction losses of the induction system; air and fuel passing through a filter and some tubes. When the throttle is partially closed, the manifold pressure drops, and the drop in pressure in effect is working against the piston on the intake stroke. The engine is working to produce a certain amount of vacuum.

With a higher hp engine, in general you would run with the throttle closed off more to lower the hp. That, coupled with either larger diameter pistons or longer stroke, equates to more power absorbed in pumping the air/fuel mixture. Diesel engines have no air throttle and do not suffer these losses. I understand some BMW engines also eliminate this with valve timing that allows air to pass out of an open valve on compression at anything less than full throttle. I understand they have 15-20% better economy at low hp. Neat idea, but hardly new. Old "hit and miss" engines of the late 19th/early 20th century used this to regulate engine speed.

No, I'm not an engineer, but somewhat of a historian. I also was senior tech writer for Cummins Engine Co. Hope the explanation helps.

Bob Kelly

Ah-ha! Thank you very much, Bob.

So the technique of flying around at WOT, but regulating HP with rpm is very valid. Jan Eggenfellner developed the idea with his engines and most of us do it.

Set WOT at take off and forget about it. Want to fly at max economy, bring the rpm back to 1700 and watch the fuel flow drop to 6-7 gph, need to climb, reset the rpm to 2300-2500 and fuel flow goes up to 12-14 gph along with HP.

So, the pumping loss would be zero with this technique.

Obviously, it only works with a constant speed prop. Pumping loss is most apparent with a 0360 and fixed pitch flying around at 2200 rpm. However, with CS prop, rpm could be set at 2200 at WOT, just like the Subaru technique.

Years ago, there was a rule to never run less rpm than manifold pressure, i.e., 23 inches, 2300 rpm minimum. Wonder if that still is a rule with Lycoming? It may be WOT and low rpm is possible only with a knock sensor.

 

[Ironflight]

Years ago, there was a rule to never run less rpm than manifold pressure, i.e., 23 inches, 2300 rpm minimum. Wonder if that still is a rule with Lycoming? It may be WOT and low rpm is possible only with a knock sensor.

From all I have read, the "over square rule" was pretty much a myth (at least until you reached extremes). After all, the numbers (25/2500, 24/2400, 23/2300....) only look "square" if you are measuring with "inches" - it's just an accident of the units. What if you were using bars, millibars, or radians per second?

Thanks Bob K for the best explanation of pumping losses that I have ever read - I think I even understand it!

Paul

 

[Bryan Wood]

From all I have read, the "over square rule" was pretty much a myth (at least until you reached extremes).
Paul

In Deacon's articles "Pelicans Perch" he has a section on props driving the engine which addresses this. It's been a long time since reading it, but he explains why it is a no no if your flying a radial. If you haven't read it Deacon explains thoroughly.

http://www.warmkessel.com/jr/flying/td/jd/78.jsp

Regards,

 

[BOBM]

Maybe not Lyc

Set WOT at take off and forget about it. Want to fly at max economy, bring the rpm back to 1700 and watch the fuel flow drop to 6-7 gph, need to climb, reset the rpm to 2300-2500 and fuel flow goes up to 12-14 gph along with HP.

If you look at the Cafe Foundation flight test of the RV9A with 160 carb Lyc, pages 6-7 http://cafefoundation.org/v2/pdf/rv-9a.pdf
you will see that 2600rpm produces 30mpg while 2300rpm only gives 27mpg. Both tests at 8500 wot & lop. Lower rpm gives 3 mph more tas but .6gph higher ff. Note that they are burning 6.1 gph at 180 mph with a carb O320. These Cafe tests are the most meticulous & highly instrumented flight tests that I know of.

 

[Russ McCutcheon]

Now WOT at sea level or 1000? with the prop pulled back to 2300 rpm would be extreme right? I guess its no different then taking off with fixed prop running 2300 rpm and WOT but is this acceptable for extend cruse?

My angle valve 200 HP CS RV-4 never sees WOT except take off and above 9000? where my cruse manifold pressure reaches WOT and then begins to fall off from there on up. Also 9000? and up is where this package shines in both speed and economy over its 160 HP fixed brothers, I?m typically about 20mph faster then my Dads -4 at 10,000? and on a two hour leg burn a gallon less fuel, two hours for me but 2 hours 15 for Dad so he is burning fuel for longer and also spends more time climbing at a slow ground speed then I do. He has a new fuel flow gauge that is not yet calibrated so when he gets this going it will be interesting to see how they compare at 1000? and the same speed.

 

[Andy_RR]

pumping work

Pumping work is only part of the equation - there are other 'curves' at play which influence the efficiency. For example, for the same power level:

- pumping work increases with increasing engine speed and swept volume as has been discussed
- engine mechanical friction power also increases with increasing engine speed
- heat transfer to the combustion chamber surfaces decreases with increasing engine speed
- ignition (effectively) advances with increasing engine speed and increasing load for fixed angle ignition systems, increasing the work done each combustion event.

Stir all these together and you will get a trail running through the engine speed/load map that represents the most efficient speed/load to develop the required power. This is why decreasing engine speed doesn't necessarily improve fuel consumption.

For the same power, a larger engine will not only have more pumping work, but also will be further from the optimal igntion timing than a smaller engine - even if you have clever electronic engine speed-related ignition advance.

A

 

[mgomez]

...but to give a number:

For every "Hg of manifold pressure difference, an O-360 running at 2400 RPM requires about 1/2 HP to overcome pumping losses. Here's the math:

Power = pressure loss x volumetric flow rate

Pressure loss = 1" Hg = 3386 Pa
Volumetric flow rate = 360 in3 x 2400/60/2 (the /2 is because it's a four-stroke)

Convert that to metric units (to make the math easier) and you get ~0.0.12 m3/s

So the power lost to pumping is about 400 W per "Hg of MAP...about 1/2 HP.

I don't know how far you have to throttle back an O-360 to make it "look like" an O-360, but if you do know, multiply the difference in MAP by 1/2 HP and you have your answer.

I suspect the difference in efficiency, if any, lies elsewhere.

 

[David-aviator]

In Deacon's articles "Pelicans Perch" he has a section on props driving the engine which addresses this. It's been a long time since reading it, but he explains why it is a no no if your flying a radial. If you haven't read it Deacon explains thoroughly.

http://www.warmkessel.com/jr/flying/td/jd/78.jsp

Regards,

That's my reference line on the subject. A long, long time ago as a KC-97 co-pilot, if ever a pilot pushed the throttles up without calling the engine room for increased rpm, you could get your arm broken by the F/E.

(The 97, by the way, was imho the most awfull airplane ever built. With those incredibly complex 4360's, there were more moving parts than anyone could keep track of in flight. I was assigned to it out of a single engine jet and almost quit flying - such a nightmare that thing was - at least one engine failure on every 4th flight.)

Seems like the reports here support the theory that there is some efficiency loss with a partially closed throttle. The CAFE 0320 report supports it, and so does the RV-4 CS above 9000'.

But that does not equat to long engine life, only efficiency. Auto engines almost never are run at WOT and for sure last a long time at 55 mph. That's why I have questioned Jan Eggenfellner on this technique. There has to be more pressure in the combustion chamber at WOT as opposed to less manifold pressure. When I really want to save fuel but enjoy local flight, I do close the throttle just a little to get the thing into closed loop. That may not be the most efficient thing to do in mpg, but it probably will make for a very long engine life as it approximates cruising down the hiway at 55 mph.

This of course has nothing to do with Lycoming technique. But like Russ's statement, when I was flying with the 0360, it was at WOT only for take off and above 8500'. The first thing after take off was throttle back to about 25 inches. I babied that thing and it probably liked it from a longivity perspective. Even now knowing more about pumping loss, I don't think the technique would change for me nor would I choose a 0320 over a 0360 because of pumping loss. The 0360 will last longer with the throttle pulled back a little and the airplane will have better take off and climb performance.

 

[Ironflight]

In Deacon's articles "Pelicans Perch" he has a section on props driving the engine which addresses this. It's been a long time since reading it, but he explains why it is a no no if your flying a radial. If you haven't read it Deacon explains thoroughly.

http://www.warmkessel.com/jr/flying/td/jd/78.jsp

Regards,

Thanks for the link Bryan - I hadn't read that in a long time - good refresher!

I'll have to rememebr that when I decide to build somehtign with a radial...

Paul

 

[BOBM]

Seems like the reports here support the theory that there is some efficiency loss with a partially closed throttle. The CAFE 0320 report supports it, and so does the RV-4 CS above 9000'.

Note that in the Cafe report, they did NOT close the throttle. They merely reduced rpm to 2300 & gained speed but lost fuel economy in the process. This is the reverse of what you would expect.

 

[rv6ejguy]

As Andy pointed out, pumping losses are only part of the picture. Best engine efficiency is a composite of frictional, pumping losses, ignition advance and volumetric efficiency. WOT always produces better SFCs than closed throttle assuming equal AFRs, mixture distribution and optimized ignition advance. Propeller efficiency also comes into play here if using a lower rpm, blade angle and twist may undo any gains to be had in the engine department.

In autos, SFCs may be up to 35% worse at cracked throttle cruising compared to WOT for instance. BMW's Valvetronic system eliminates the throttle plate altogether, boosting cruise SFCs a reported 25%.

Generally speaking a smaller engine of the same design, operating at a higher throttle opening will use less fuel to produce the same hp as a larger version at lower throttle openings.

Supercharged and turbocharged engines have the advantage of offsetting pumping losses by using compressor pressure to drive the pistons down during the intake stroke instead of the crank having to pull them down. Lower SFCs on these engines are almost always at high MAP and lower rpm.

 

[Yukon]

No Free Lunch

To summarize the preceeding posts - "There is no such thing as a free lunch"

Want a big motor.....get a big Chevron card.

 

[jcoloccia]

BTW, pumping losses refers to ALL of the pumping action of the pistons. This includes intake and exhaust. Basically, all of the work nescessary to do the pneumatic stuff the engine has to do is called "pumping loss". You still have pumping losses at WOT but it's minimized. Now, what this has to do with choosing an engine is lost on me. As Dan's show time and time again, if you design the SYSTEM properly, and operate it properly, you will get very high levels of effeciency regardless.

 

[mgomez]

Now, what this has to do with choosing an engine is lost on me.

I think it refers to the old argument that using an O-360 results in less efficiency than an O-320, if flown at the same power, because the O-360 is throttled back more. You're therefore spending more power to pull air past the obstruction of the throttle blade. But as you said, there are other places where the engine expends energy to pump gas (such as out the exhaust.)

I was trying to show what that difference is...and it's not much. It's probably lost amidst the various other choices we can make that affect efficiency.

 

[osxuser]

To summarize the preceeding posts - "There is no such thing as a free lunch"

Want a big motor.....get a big Chevron card.

Not really, see:

I don't know much about effciency other than that. I do know however that Lycoming suggests that for best life, the engine should be run at lower power settings most of the time. Therefore, running an O-320 hard will shorten it's life. At 75% power the O-320 will put out 120HP, the O-360 will be at 66.67% HP and a IO-360 (Angle Valve) would be at 60% power.

This would lead to longer engine life according to Lycoming. Fuel effciency would be higher with the IO-360 assuming you don't have a problem running LOP, which you wouldn't be able to do at 75% with the O-320 (Or even with an IO-320).

Go higher, WOT with the IO-360, run 60% Power (controlled by RPM) and LOP. Save gas, and have the power when you need it. O-320 won't be able to run LOP because the % of power to maintain the same airspeed is too high for LOP.

 

[Yukon]

Read the Posts Stephen

Stephen,

Have you taken the time to read any of the other posts? Lots of scientific evidence this is not true, just forum-speak for "I want the biggest engine the mount will tolerate". If this were a fact, do you suppose Lycoming would be building so many different sized motors? Why does the 152 have an O-235 and the Skylane RG have a O-540? Look at the overhead that could be saved by putting the same size motor in all airplanes.

This is the kind of rationalization that needs to stop. These airplanes have been designed and tested by a very competent aircraft designer. Following his engine and gross weight recommendations are important safety issues.

 

[Russ McCutcheon]

Sorry John but your example has no bearing on this discussion, we are discussing different engine options on the same airframe not a 152 verses a 182, theses aircraft are of very different size, weight and mission. An RV-7 excepts from 150 to 200 HP as designed, the discussion started with pumping losses of the bigger engine compared to the smaller engine and went on to a general comparison of these options. As for a free lunch, did you read everything? It is very obvious that on a high cross country the big engine wins both in speed and fuel burnt and may win or loose at low level and same speed depending on the operator and other factors but it will be close. Where not talking the difference between 200 CID and 540 CID on a plane weighing over twice as much, where talking 40 CID difference and the same plane, try and keep it real.

 

[Yukon]

Engine size

No Russ, the thread is addressing how big an engine to install in an RV-9. That's where my hypothetical about the 152 comes from.

 

[Russ McCutcheon]

Looking close I see Steve is building a 9A but this is still a valid discussion and many people have used -360s in the 9 with great results and they are free to do so being experimental, I will not have a -9 because it is not aerobatic but if I did it would have a 360. Compared to a super 8 twenty extra HP in a 9 is not a big stretch, but this argument has been beaten to death over and over and was not directly the topic in this thread.

 

[LifeofReiley]

Not 20 HP

Looking close I see Steve is building a 9A but this is still a valid discussion and many people have used -360s in the 9 with great results and they are free to do so being experimental, I will not have a -9 because it is not aerobatic but if I did it would have a 360. Compared to a super 8 twenty extra HP in a 9 is not a big stretch, but this argument has been beaten to death over and over and was not directly the topic in this thread.

Russ,

You're not going to get 20 extra HP with a stock O-360 (180) vs a stock
O-320 (160)... as a representative it would be 40 ci more in displacement, maybe 12 hp. It's could be possible with a derated 150 hp O-320 I guess.

 

[osxuser]

Always pushing

John,

Constantly pushing buttons aren't you. He didn't ask specifically about the -9, as such, I didn't address any specific airframe. He specifically asked about 320 vs. 360, and I answered that. All theoretical aside, the concept has been proven by side-by-side fly-offs, O-320 vs. IO-360.

If you want to restrict a O-360 (Parallel Valve) to 2400RPM it is then rated at 160HP. That is done with prop pitch. That would make it Kosher for the -9, if that's the route you want to go.

 

[Russ McCutcheon]

Darrel,

You may be right, if so then even less of a big deal installing one in a 9. I don?t have a dyno but the rated HP is 160 verses 180, that?s 20HP difference so how do you come to the conclusion it would only be 12 difference? If you turned them both to rated RPM would they not produce there rated HP? I wouldn?t be surprised if they didn?t but I don?t know.

Russ

 

[gmcjetpilot]

Engineer speak

Too many variables and not enough equations:

Rule #1 for engine guys: There Ain't no replacement for Displacement.

Most piston gas engines run BSFC of 0.38 to 0.46, where BSFC is:

BSFC = Fuel Flow (PPH) ? Horsepower
or BSFC = 5.92 x Fuel Flow (GPH) ? Horsepower​

0.38 is not likely but possible. Air cooled Lycs standard spec or typical is 0.43-0.44, but go up to over 0.51 at high power (or real low power). There seems to be a golden range of about 58% power to 65% power. Any power more or less is worse BSFC. Over 75% or less than 50% BSFC gets worse. Full power BSFC is over 0.50.

Example: O320 99% power Vs. a O540 at 61% (both about 160 hp), there will be a significant difference in BSFC, my est is over a 1 gal/hr! A 160HP v 260 HP is not practical because the airframes are going to be different. If the Rocket guys who fly real slow can save fuel. The con of big iron is more weight that eats into the this theoretical BSFC calc advantage, but clearly there is an advantage on paper.

Example: How about 150hp to 180 hp, where the 150hp is at 73% power and the 180p is at 58%, the difference is smaller but could be 0.10 gal/hr.​

There are other things to improve BSFC, LOP, EI, higher compression, better intake & exhaust, but overall an engine's BSFC is set by its design.

A 320 can be as efficient as any larger engine but its just flying slower and/or lower, BUT over all the 320 should burn less fuel than a larger displacement Lyc. 50% power on a 320 is about the same BSFC as a 50% power on a 540. Of course 50% power on a 540 is more FF than a 320's 555. If the 320 is asked to keep up with the 540 plane, than the 540 might have a slight edge, especially if the 320 is over 75% power and can't lean.

All Lycs, 320, 320, 540 and 720 are similar (cylinder assemblies), so there is not going to be significant difference in BSFC. Of course the angle valves are more efficient overall because of the better flow (volumetric efficiency) and higher compression pistons, but they also weigh and cost more.

Comparing similar Lycs to Lycs, it really comes down to practical aspects, operational needs and techniques, more than efficiency gained by flying at low power. Howerver rule #1 applies..

OPERATIONS?

With the large engine you can fly higher at higher TAS. However you may be into sup O2 breathing altitudes to take full advantage (by flying at low power WOT). Of course airframe flutter margins may come into effect with a RV9. Look at Van's spec for service ceiling. Clearly more pony's can fly higher and/or faster. If you live in the flat lands you don't need a big engine. Denver, I'd get the big engine.

IF you are going for more "efficiency" (mpg and BSFC) than a large engine could have a slight edge but requires the pilot to operate in a very specific and careful manner (slow). In general big engine = big fuel bill, but you will get there faster.


THE BEST TEST IS REAL WORLD

The 320/360 vs. 540 comparison is not super practical because of airframe differences typical of planes w/ these engines. Rocket guys say they burn less than RV's flying formation X-C. From what the Lyc specs say that's possible. It can also be airframe drag and pilot technique. Both engine have the same "pumps" (cylinders are identical).

360 parallel valve (180hp) vs. 360 angle valve (200hp)? Dan C. says he gets better BSFC. Dan is quite the operator and his engine is fine tuned so he runs LOP. The 360 angle valve does have better airflow and probably is better suited for LOP than parallel valve engines. Again it's more operational, but design plays a part. The 360 angle valve has higher compression, which also makes it more efficient.

320 vs. 360 comparisons? Again its more operational not mechanical. If the 320 can fly its own game than it will burn less fuel but just take a few minutes longer to get there.

You can make an argument for either engine but its really many unknowns that fill in the equations. I am a BIG fan of following the planes (most of the time).

 

[RVbySDI]

thanks for the replies

I just wanted to post quickly to say that I posted this question Friday afternoon and have not been able to see this thread again until now (Monday afternoon). I will be reading your replies to see your responses. I appreciate everyone's replies and will endeavor to read them all as quickly as I can. If there are any of you that asked a question of me I will try to get back to you as soon as I can read your posts.

 

[RVbySDI]

More information

Guys,
I really do appreciate all of the input. I would like to try to clarify the motivation for my question so that perhaps I might receive even more input from all of you. Yes, even from Yukon the eternal button pusher. All of you replied with some very informative information and I truly appreciate the formulas presented. That is very much some of the things I wanted to read.

However, let me expound upon my thinking that lead to this post. I am not interested in putting a 720 in my 9. Nor am I thinking of making a rocket out of it with th 540 or anything of the sort. Heck (closest I try to get to those curse words), I am not even thinking about the 360, angle or parrallel. No, what I am thinking about is the ECI IO-340. I really do like this engine a lot. I think from what I have read it would be a great engine to put in the 9. But I wanted some opinions from you guys who know much more about engine performance than I do.

From my discussions with the guys at America's Aircraft Engines and ECI at Oshkosh they are saying the IO-340 will weigh approximately the same as the O-320 but put out somewhere between 180 and 185 hp. So, I understand about the "there is no free ride" issue but if this is the case this seems like a win-win situation. Thus my question about the pumping losses and the issue of the difference between two similar engines. If the IO-340 can run at 55% to 60% and put out HP in the same ballpark as the O-320 would be at say 75% then would the IO-340 be the better engine for efficiency, longevity etc. I am interested in hearing from you guys on what you think the pros and cons are for such a comparison.

And before Yukon or others pipe in about how bad I am for thinking of doing such a bad thing, yes, I do understand all about the design limits of the 9. I understand about the flutter issues of exceeding Vne, structural issues of excessive speed during manuvers and the like. However, I am interested in flying this 9 in and out of high mountain country where having the hp advantage may be very useful. I am interested in flying out of short fields in July and August when the temperatures are measured in triple digits and the humidity hovers around the "That can't be sweat!!! It looks like you just jumped into a pool with all your clothes on" levels. I am not interested in acro, in raw speed, in playing with the heavies in the flight levels. I am interested in climbing to altitude, setting the autopilot slaved to the GPS and going across country as quickly, efficiently and as comfortably as I can. Then landing and taking off again on any patch of smooth surface that has clear skies on both ends or at least enough clearance to get my bird back into the air so it can climb out without worries of whether it can or cannot do it.

 

[kentb]

It may be a good idea

If that engine would have been available when I was choosing, I would have certainly looked at it.
The one question that I would want to explore is: service. How does it differ from the 320? Where do you get any unique part and will there be a cost difference.
I like the idea of a little more power although I don't think that it will be needed.
I managed to get my IO320 as a rebuilt engine and prop for $19,500.00. I then spent all the savings on my panel. I should have go simpler on the panel and put some of the money back into the bank.

With my engine / prop, I have departed 4200 ft elevation airport on 85 degree day and easily managed 1400 ft/min VSI. I have also been able to cruse at 189 mph.

Kent

 

[osxuser]

I don't think you'll have issues with the IO340 in a -9. The higher compression ratio will help with efficiency. And with only 20 more CI, I doubt it would make a real pumping difference anyway.

 

[LifeofReiley]

Guys,
I really do appreciate all of the input. I would like to try to clarify the motivation for my question so that perhaps I might receive even more input from all of you. Yes, even from Yukon the eternal button pusher. All of you replied with some very informative information and I truly appreciate the formulas presented. That is very much some of the things I wanted to read.

However, let me expound upon my thinking that lead to this post. I am not interested in putting a 720 in my 9. Nor am I thinking of making a rocket out of it with th 540 or anything of the sort. Heck (closest I try to get to those curse words), I am not even thinking about the 360, angle or parrallel. No, what I am thinking about is the ECI IO-340. I really do like this engine a lot. I think from what I have read it would be a great engine to put in the 9. But I wanted some opinions from you guys who know much more about engine performance than I do.

From my discussions with the guys at America's Aircraft Engines and ECI at Oshkosh they are saying the IO-340 will weigh approximately the same as the O-320 but put out somewhere between 180 and 185 hp. So, I understand about the "there is no free ride" issue but if this is the case this seems like a win-win situation. Thus my question about the pumping losses and the issue of the difference between two similar engines. If the IO-340 can run at 55% to 60% and put out HP in the same ballpark as the O-320 would be at say 75% then would the IO-340 be the better engine for efficiency, longevity etc. I am interested in hearing from you guys on what you think the pros and cons are for such a comparison.

And before Yukon or others pipe in about how bad I am for thinking of doing such a bad thing, yes, I do understand all about the design limits of the 9. I understand about the flutter issues of exceeding Vne, structural issues of excessive speed during manuvers and the like. However, I am interested in flying this 9 in and out of high mountain country where having the hp advantage may be very useful. I am interested in flying out of short fields in July and August when the temperatures are measured in triple digits and the humidity hovers around the "That can't be sweat!!! It looks like you just jumped into a pool with all your clothes on" levels. I am not interested in acro, in raw speed, in playing with the heavies in the flight levels. I am interested in climbing to altitude, setting the autopilot slaved to the GPS and going across country as quickly, efficiently and as comfortably as I can. Then landing and taking off again on any patch of smooth surface that has clear skies on both ends or at least enough clearance to get my bird back into the air so it can climb out without worries of whether it can or cannot do it.[/QUOT

180-185 Hp at what RPM? 3200 at 100 MSL?

 

[RVbySDI]

180-185 Hp at what RPM? 3200 at 100 MSL?

ECI states the 180-185 HP is at 2700 RPM.

The one question that I would want to explore is: service. How does it differ from the 320? Where do you get any unique part and will there be a cost difference.

The difference between the 320 and the 340 is in the increased length of stroke for the piston. The 340 has a slightly longer rod and appropriate modifications to allow for this lengthened stroke. The bore is the same as the 320. The compression is higher than a stock 320 but I believe they may use a high compression 320 piston.

 

[osxuser]

Different crank, different rods, different cylinder assemblies.