Wesael

Wesael

Well Known Member
Has anyone here specificaly measured the effects of compression ratio alone in relation to HP on a Dyno?

I tried to search Lyc. for information and have not found anything proven specificaly.

In a seperate thread Malon seems to indicate a 5 hp increase in the 360 engines when going from 8.5 to 9.2:1 ratio but that seems like a general figure.

If I divide 5hp by 180 hp we get a 2.78% increase in that particular ratio increase.

If we use the angle valve engine with 200 hp. 5hp by 200 hp we get 2.5% increase.

can these figures then be expected when raising the C/R of the 540 engines?

Kevin? Dan? Thomas? you guys seem to have checked out a lot of these details that I am interested in.
 
Weasel,
I have not done a piston swap (compression ratio change), then a dyno pull to get data results yet. However, I plan on freshening up the top on this O-360-A4A (peanut drone engine) and if the pistons are lower than 8.5, I plan on changing them to that, since I have extras. Should produce some good comparison data.
 
Hi comp

When my 0-320 E2A was rebuilt I went with 9:1 pistons. It wasnt dyno'd but with the 160 club installed it pulled 75 more static rpm than a 160hp engine. I dont know how to determine Hp from RPM.
 
Beancounter said:
When my 0-320 E2A was rebuilt I went with 9:1 pistons. It wasnt dyno'd but with the 160 club installed it pulled 75 more static rpm than a 160hp engine. I dont know how to determine Hp from RPM.
Click to expand...
Well, you do need RPM and TORQUE but once you have those two you can calculate HP. Here is the formula:

2π(T)(RPM)
----------- = HP
33000

where:
π = 3.14157 (pi)
T = Torque

If you know the TORQUE at a specific RPM you can determine the HP at that specific "power" setting. The documents for your specific engine should have a power curve graph where you can extrapolate these numbers for your engine at any given power setting.
 
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O-360-A4A (peanut drone engine)
Wesael said:
:D:D:D:D:D:D
Click to expand...

Well after running the supercharged 540, the O-360 drone motor received the name of peanut. Because it just look small? The final numbers of the last dyno run before it came off last weekend were. Un-corrected @ 8218 density alt. 2650rpm: Torq. 657ft-lbs // 331.37hp. Installation in process, will be flying to KOSH.
 
If you increase compression ratio above 8.7:1 it is recommended that the timing be retarded by 5 degrees from standard so it is likely that some of the power increase from the higher CR will be lost by retarding the timing.

Have a look at this thread I started some time ago. Also in Post #6 Kevin gives the CR HP formula.

Fin
9A
 
timing

On the parallel valve Lycs I hav never heard of retarding the timing for high compression. With the electronic ignitions, at cruise power settings at altitude, the timing can be advanced far beyond 25 degrees. At altitudes in the 17-18,000' range I have heard of timing approaching 35 degrees with pilot controlled advance.
The angle valve four cylinders call for timing at 20 degrees.
 
jrs14855 said:
On the parallel valve Lycs I hav never heard of retarding the timing for high compression. With the electronic ignitions, at cruise power settings at altitude, the timing can be advanced far beyond 25 degrees. At altitudes in the 17-18,000' range I have heard of timing approaching 35 degrees with pilot controlled advance.
The angle valve four cylinders call for timing at 20 degrees.
Click to expand...

Hi folks, first post on here. The 1E10 type certificate on the angle valve Lycoming IO-360 engines lists 25 degrees as the timing, with 20 degrees optional if the lag angle is changed on the magnetos. 20 degrees is not allowed on the -A3B6D dual mag engine.
 
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Timing info:
Here?s what I found on ignition timing testing for my supercharged application. Main test was to determine detonation and/or pre-ignition: Test equipment used was a adjustable sensitivity knock sensor located on #1 cylinder spark plug base, also a condenser microphone. To record engine sound from the same location, digitally recorded to load into sound software to be graphed out on time lines. Cylinder head temperature and mixture plays an important role in controlling detonation and pre-ignition.
540-C4B5 8.5:1 compression ratio.
Cylinder head temp 365f.
Base timing @ 25degrees BTC (No timing changes during testing)
Findings were:
No detonation up to 35?mp
36?mp very slight controlled reduced with increased fuel flow
36.5?mp still slight, more though, no response on adding fuel
37?mp Detonation present, un-controllable in the RED on the read out and sound recording.
My rule for operating on the timing curve is to remove 1 degree of timing / 1?mp increase above 35?mp
I know this info., is specific for my app., however shows, Lycoming timing recommendations are conservative in my opinion.
 
I will preface here by makin it clear that I have only begun to work on airplanes, so my experience is with land based IC (internal combustion), mostly spark ignition, engines. But, they all obey the same laws of physics.

So getting back to the OP's question, the reason you can't get a straight answer is becuase there isn't one. The thing is, what makes an IC (internal cumbustion) engine work well is the combination of air, fuel, spark, engine (or piston) speed, timing of all of this (not just ignition), etc. Static compression is what is being discussed, however, dynamic compression is what really matters. The reason it is rarely discussed is because it is hard to explain and harder to measure.

Static compression ratio is simply the cylinder volume at BDC divided by the cylinder volume at TDC. Dynamic compression ratio, in simple terms, is the volume of the cylinder when the intake valve closes, or almost closes, divided by the volume of the cylinder at TDC. There are other factors, but this is close enough.

In very simple terms, assuming at least most other things being equal, higher static compression means you can run more agressive cam profiles or cam timing and, possibly, make more power. In racing engines, this can be used to squeak out that last few percent of performance. In engines that you expect to last a long time, it may not be worth tweaking that one parameter to get every ounce of HP with the risk of detonation, especially if you expect your engine to run reliably at 2,000 hours, just like it did at 100 hours. The one advantage with land based engines is you can generally hear the detonation before things go way south, and of course you can always just pull over. YMMV.

I am all for experimentation and pushing the envelope, but race engines are different animals running under different expectation limits than engine intended to haul people enjoyably and reliably over a long operting life. Just be informed and make your decisions wisely.

Tim
 
Hello fellas.

Have fun reading this. Because that's what I'm doing.

I am rebuilding a IO-540-C4B5 engine for myself to put in my own toy as an A&P IA.

See you fellas talking about compresssion ratios here. Enjoying the thread. Love the theory.

If I had lots of money to pay for the time, or acces to a friends dyno, (don't have a friend like that) I would love to see what the difference of just the one change doing nothing else to timing, carbureation or injection, nothing, just pulling the jugs and putting in the higher compression pistons etc.

All the theorizing aside. (which I love) we know higher compression within reason works.

We have seen certain high profile people do it with not much else wise done.
At least not much elswise done which would have much affect on the difference between 8.5 to 9.5. We are just interested in the rough difference.

Not theorizing for ever about all the differences and never get an engine together.

We see the differences in Hale's engine and Patties engine after magician Captain Barret and family massages them.

Again within reason, we know compression ratio raises work.

Not going too far over board.

I see 9.5 as my limit with available fuel and I guess would keep my std pistons for the future depending on fuel availability. I guess. Seems a waste.

But, I would like to build up my engine and put in the standard pistons that come with the new cylinders...
Dyno it. Then with the engine in the dyno pull the jugs and put in my choice of pistons and see the changes.

Then after seeing the major change or gain. I would know what a certain amount of extra compression from these parallel valve cylinders
will get from the standard like 8.5:1 to 9.5:1. I am sure someone knows. The real engine builders.

Then after putting in the 9.5:1 and seeing the standard change, then start playing with all the variables, electronic ignition compared to my standard mags, which I assume will be only better starting and low end pop as compared to top end where I assume/but will find out the elctronic mag fellas have all that figured out at the top end. I've heard on some standard electronic ignition systems out there, the top end spark timing is basically set at where a normal mag would be at top end. I assume close to standard at top but that doesn't matter right now. Wow to be able to adjust your own timing in flight with all the sensors.

I would like to do the electronic igniton mainly for easier start up especially with 9.5:1, and the newer lithium batteries and specialty starters, with a big thick and short battery cable.

But I just want to fly and have the power for the aerobatics when I want it.

Of course there would be a little differences in the run for breaking in temp everything the theories bring into thought.
But I am not interested in finite numbers. Just the rough numbers. I can't fly that finite anyway.

And when do we in the regular life of our toys actually fly 1800 hours without doing something to the cylinders anyway
unless it is over twenty years.

I am planning that I am going to have to take off my cylinders at some point before a 1000 hours mabe 800.

I want ot play and have fun. And I am going to pay for that fun. It's just money and we only live once.
And I'm a very squeaky stingy person but I live for this fun and thats what I want.

I am looking at ECI and Superior cylinders as well.

I am looking at cold air induction, RSA-10 fule servo, the 9.5:1 forged pistons with ECI new cylinders, 6 into 1 exhaust by SkyDynamics. Would hope to do Electronic ignition but don't know which one. Would want the Gami Ignition if they EVER come out with it. You know it senses combustion pressure and adjusts timing. I would think someone else would have come up with it since they started working on it since 2002. It is 2012 now, and they could have tested it on the open market in experimental first..

Don't know what HP all that would bring but I'va an idea.

I would like to put on the Airflow Performance FM-200 fuel system. But we'll see if I can find one cheap, Yeah right.

I don't even know yet if I can move the RSA-5 or -10 from the bottom of the engine with straight up induction and move it to the front of the cold air induction so air flow comes in from the front. I would imagine there is a modification to the stock RSA-5 I have, or find the right RSA-10.

I also imagine from my kiddie car hot rod days at a younger age the smaller RSA-5 will accelerate of the birm faster and then peter out where the RSA-10 will not have as much off the birm pop that I want. But I need top as well. We'll see.

This is all back yard red neck mechanic theory. But going to do it anyway regardless. Then I'll know. I have done mostly certified and warbird engines all my life and never been able to play like this.

But main things is. I would love to put it together however, put in the std pistons, dyno. And then put in the 9.5's and then see the simple difference.

But then we would have to shelf the standard pistons for whos know what and when to use them again.


I was looking at forged pistons from Combust Tech http://www.combustech.com/Products/Lycoming Pistons.html

p.n. ASC9521FL
9.5:1 Compression Ratio - for Parallel Valve 5.125 Bore

If we are buying new cylinders that come with everything except piston pins,
Has anyone had any thoughts about if we want the higher compression pistons, how do we get the new cylinders assemblies, but without the compression standard ratio pistons.

Any luck getting them to keep the standard pistons for a certain price and or get the piston ratio you want?

Looking at the cost of buying the cylinder assemby and having a wasted new std piston sitting on the shelf, when you are going to buy the higher compression pistons.

what to do with the std, or get the distributor to keep them and give you a 150 or so off the standard price?

Any luck with that scenario? :D

I just want to play. And am going to have to pay.
Don't flame me, take it with a grain of salt. I have worked rebuilding aircraft and engines to standar my whole life and this is the first time I have had the chance to play and not have things standard to spec. Play a little and see where it goes and enjoy. Just want to see how the differences work out comapred to how we off the cuff think they will turn out.

It's not rocket science. It's enjoy an experimental airplane science. And wear a parachute and practice down at the closest jump facility what it is really like jumping out of a plane if we had to. Practice practice, but don't do anything other than what we are trained to do saftey wise.

But we know compression ratios work within reason or there would be detonation and too much pressure at the top end. I don't think normally asperated / injection at 9.5:1 goes too far overboard with 100 octane only. As well as electronic ignition for start up.

Mike Robinson
 
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Cylinder Ultimate Pressure

Just curious ---- what would be the highest internal pressure (psi) a cylinder would see, during the combustion process? Use a NA IO360, 8.5 to 1, running on 100LL as an example.
 
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