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Piston/compression/fuel combinations for O-360 and O-320

Sam Buchanan

been here awhile
This info was originally submitted by Mahlon Russell:

7:1 compression ratio, in an O-360, is had by installing 75413 or equivalent pistons and it is generally accepted to burn mogas with 87 octane and above with that compression ratio. Take off Hp is in the range of 168 with those pistons.

8.5:1 is the standard compression ratio for the O-360 and it is attained by use of 75089 or equivalent pistons. It is generally accepted to run mogas of 91 octane and above with this compression ratio. Rated power is 180 HP with those pistons

9:1 compression is attained by use of the LW-15357 or equivalent, in the O-360, and it is generally accepted that you should use 100LL r above with this engine. Normally see around 185 HP at take off, with those pistons.

The 320 and the 360 have the same bore, only the stroke is longer on the 360 to get the extra displacement. So you use the same pistons to get the same compression ratios for the 320 as with the 360.

7:1 compression ratio, in an O-320, is had by installing 75413 or equivalent pistons and it is generally accepted to burn mogas with 87 octane and above with that compression ratio. Take off Hp is in the range of 150 with those pistons.

8.5:1 is the high compression ratio for the O-320 and it is attained by use of 75089 or equivalent pistons. It is generally accepted to run mogas of 91 octane and above with this compression ratio. Rated power is 160 HP with those pistons

9:1 compression is attained by use of the LW-15357 or equivalent, in the O-320, and it is generally accepted that you should use 100LL above with this engine. You should see around 164 HP at take off, with those pistons.

Good Luck,
Mahlon

“The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
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Thanx, Sam!

And all this time I thought the difference between the -320 and -360 was in the bore size. Amazing how much you can learn browsing these forums.
 
Mahlon

For those who wonder who this guy Mahlon is, and "why should I pay attention to what he says??", well, see for yourself.

Click Tech Advice on left.
 
Mogas in a normal O-360?

So if I read this right, 91 Octane MOGAS "should" be okay with a stock (180 HP) O-360 with 8.5:1 pistons.

How about seals in the carburetor, fuel tanks, etc? From my limited knowledge of auto fuels, the big issue is to make sure it does not contain any ethanol or alcohol solvents. These will eat into some of the seals used throughout the fuel system, at least that's the rumor.

As for the tanks, I think I've read auto fuel is okay if you didn't slosh the tanks . . .

Curious what everyone else thinks about MOGAS in a Lycoming. I know this has been discussed before, but there seems to be more support these days than in the past.

Any thoughts?

Rick
 
So if I read this right, 91 Octane MOGAS "should" be okay with a stock (180 HP) O-360 with 8.5:1 pistons.

How about seals in the carburetor, fuel tanks, etc? From my limited knowledge of auto fuels, the big issue is to make sure it does not contain any ethanol or alcohol solvents. These will eat into some of the seals used throughout the fuel system, at least that's the rumor.

As for the tanks, I think I've read auto fuel is okay if you didn't slosh the tanks . . .

Curious what everyone else thinks about MOGAS in a Lycoming. I know this has been discussed before, but there seems to be more support these days than in the past.

Any thoughts?

Rick

It is understood (I assume) that we are talking about premium fuel not fuel enhanced with ethanol.
 
I hope I'm not diverting/cluttering this thread... if so dump me off in a new one.

I'm rebuilding my h2ad, which has 9:1 pistons (15357). So I take it I *can* switch to 75089 pistons and still maintain 160hp?

Same pins and plugs?

Does anyone know which rings to use with these pistons, or is it the same as the 15357 rings?

Thanks!
 
No free lunch.

Sorry but if you lower compression from 9:1 to 8.5:1, you will not maintain the same hp.
The H2AD is a totally different engine.
 
How many have flown the same airplane with the same engine only to have different piston compression ratios?

Am I the only one to have used 8.5:1, 10:1, and 9:1 pistons in the same airframe and engine?

Flew an hour today for the first time in 2 months and 4 days with 9:1 pistons for the first time.

Seat of the pants, an RV-6 O-320 with constant speed prop feels the same in cruise with the 8.5:1 and the 10:1 pistons. ROC may be slightly better with the 10:1. Unable to put a hard test number on the ROC improvements. In other words, I was not able to measure any improvement in ROC. Fuel burn was less with the 10:1 if you lean aggressively. Most engine shops that install 10:1 do not recommend leaning agressively.
 
Same plane, different pistons, choosing a CR

I have flown the same airplane with the same engine, with the same fixed pitch prop, but with different piston compression ratios. My RV-6 had 50 SMOH on a parallel valve IO-360 with 7:1 pistons when I swapped for 9.5:1 pistons.

My experience seems different from yours, Sam. My RV-6 has never had a constant speed prop. I only flew with the 9.5:1?s for about 2 hours before it became clear to me that I needed to replace that beautiful Warnke fixed pitch prop. My hazy recollection is that the new pistons added about 200 RPM, at WOT, in level cruise, at the same altitude, in similar atmospheric conditions. The testing was not scientific, precise, or repeated. It was, however, consistent with a rule of thumb used by Ed, at Sensenich, when I purchased a new 72FM with 85? of pitch. FYI, my particular application is NOT approved by either Ed or Sensenich.

This thread is ?Piston/compression/fuel combinations for O-360 and O-320.? My understanding is that the purpose of the thread is to help others, perhaps like Andy, select an appropriate compression ratio for their engines. Sam, quite accurately I think, reports that ?Most engine shops that install 10:1 do not recommend leaning aggressively.? That?s information I wanted to know when I was choosing a compression ratio for my engine. But, when I was making my choice, I also wanted to consider real world performance information. I wanted to know, ?How much difference will it likely make if I do, against the engine shops? recommendations, lean aggressively??

My operating practices seem to differ from the engine shops? recommendations. Maybe there?s an important distinction between my 9.5:1 pistons and those engine shops? 10:1 pistons. I?m not sure. Maybe I?m just lucky. I?m not sure. I am sure that with the 9.5:1?s, I do lean ?aggressively.?

My RV-6 burns only 100LL. It?s equipped with EI?s UBG16. And, I really do use it and monitor it. The aircraft is also equipped with GAMI injectors, one Slick mag timed at 25 deg BTDC, one Lightspeed III retarded 5 degree in accordance with Klaus? recommendation for high compression piston applications, and Vetterman's crossover exhaust. With all of that out of the way, here are a couple of data points.

Example of my RV-6 with ?aggressive? mixture leaning to a repeatable power setting yielding repeatable performance: 6,500 ft MSL, WOT, GAMI?s ?big pull? on the mixture knob, 2550 RPM, mid-summer CHTs all less than 330 deg, oil temp at 180 deg, making 165 KTAS, burning 8.5 gph.

Exactly how many degrees lean of peak is that power setting? I dunno. It?s probably about 100 degrees lean of peak. Honestly, I?m a little afraid to check. I installed the EGT probes too far from the exhaust flange. They are slow to respond. At WOT, at 6,500 MSL, with the fixed pitch Sensenich, I estimate this engine will spin at least 2,850 RPM while I?m trying to precisely determine the peak EGT. It?s not worth knowing . . .

I think of this as my ?flatland-headwind-go-fast? power setting. ?Flatland? because my normal mission is 12,500 ft MSL or higher, on a 650 nm flight, over the Rockies, from Scottsbluff, NE to Las Vegas, NV. ?Headwind? because, without that factor, I?d be flying at 12,500 ft MSL--even over the flatlands. And, ?go-fast? simply because it?s WOT.

Comparison to my RV-6 with ?traditional? mixture leaning to a repeatable power setting yielding repeatable performance: 8,500 ft MSL, 50 deg ROP, 2550 RPM, mid-summer CHTs all less than 380 deg, oil temp at 210 deg, making 172 KTAS, burning 10.5 gph. These numbers are reliable for my RV-6, but I almost never use this power setting. I think of it as unnecessarily hot and inefficient.

Note that the Example is at 6,500 ft MSL while the Comparison is at 8,500 MSL.

Hopefully, these data points--in conjunction with the nearly illegible Lycoming power charts (or Kevin Horton?s excellent engine power spreadsheet), prop manufacturers? recommendations, and reports of the impending demise of 100LL--will be helpful to someone who is choosing the compression ratio that is right for his or her engine.
 
Sorry but if you lower compression from 9:1 to 8.5:1, you will not maintain the same hp.
The H2AD is a totally different engine.

Is there any way to calculate what sort of HP loss there would be? (short of the do and dyno approach) If the future of 100LL is truly in jeapordy, I'd be stupid not to at least research this option. Is there any reason why the 8.5:1 pistons wouldn't physicaly work on the h2ad?
 
How many have flown the same airplane with the same engine only to have different piston compression ratios?

I started out with 7:1 in my O-320-E3D (2515hr TT). I went to 9.5:1 at overhaul. BIG difference. Prop went from Sensenich 68X69 (W) to Sensenich 70X80 (W) then to Catto 3-blade 66X74.
 
Piston/compression/fuel combinations for 0-360 and 0-320

Wondering if anyone has any data/experience with lower compression pistons in the angle valve I0-360. Standard is 8.7:1. The turbo version uses 7.3:1. I have heard that by running 7.3:1 pistons in the non turbo version, it is ok to use mogas and that you give up about 12 HP. Anyone know whether this is true? Is anyone running 93 octane with the 8.7:1 pistons? I have been running a mix of 93 octane mogas/100LL for years with no problems. I do have electronic ignition.

John Henley, RV6 540 hrs sold, RV7 550 hrs flying
 
Is there any way to calculate what sort of HP loss there would be? (short of the do and dyno approach) If the future of 100LL is truly in jeapordy, I'd be stupid not to at least research this option. Is there any reason why the 8.5:1 pistons wouldn't physicaly work on the h2ad?
Short answer - if you change the compression ratio from 9:1 to 8.5:1, and make no other changes, the power at the same rpm and MP should decrease by about 1.6%. This would cause about a 0.5% loss in speed, and loss of rate of climb somewhere in the range of 2.5%.

Long answer - see this post for the background on that power calculation.
 
what pistons for 9.5:1

I am buying new ECI Titan cylinders for my wide deck parallel valve IO-360. I only burn 100LL and will be installing either the JPI or EI EGT/CHT monitors. What pistons should I select to go to 9.5:1 and what hp should I expect?

What are people's opinions on Nickle vs steel cylinders?

The old cylinders were high time and chromed when installed on the engine and three of them are shot and one close to it!
 
O320 piston change

Hello ,

I am wondering if it is easy to change an O-320 carburated Lycoming from a compression of 8,5:1 to 10:1 to improve use on ethanol...Have I just to change the pistons?

thanks for your help...
 
I'm a noob to airplanes (well, ones with motors anyway;), but just curious if anyone has experimented with different cam profiles to complement the different possible compression ratios.

I've some experience building motorcycle engines and have found that it takes a rather different cam profile to get the most out of a motor at one CR than at another CR. As an example, a TL1000 (1000cc v-twin) can make about 120hp with stock internals (11.3:1 CR) on 87 oct fuel. Changing cams with stock CR doesn't net any significant performance increase and any significant increase in overlap or lift/duration actually hurts. Increasing CR gets some performance but you can't go too far without knocking issues; however, bumping the CR to 14:1 and adding a considerably more agressive cam at the same time results in quite a bit more power (140ish) and it will still run reliably on mogas. Anyhow, this is a very different engine, but I wonder if the principle might be the same - if a more agressive cam might work well with more CR and vice versa.
 
Hello ,

I am wondering if it is easy to change an O-320 carburated Lycoming from a compression of 8,5:1 to 10:1 to improve use on ethanol...Have I just to change the pistons?

thanks for your help...

Yes it will work however be sure you have the heavy wall piston pins 13444-1 pin & plug assys would be best.
 
BikePilot,

BMEP is everything. Changing effective CR can be done by changing static compression ratio (piston/combustion chamber volume) and it can be affected by the cam (longer overlap = less effective compression). A couple of web sites with pretty good explanations.... http://victorylibrary.com/tech/cam-c.htm http://mgaguru.com/mgtech/power/pp105.htm And one where you can calculate effective compression ratio..... http://kb-silvolite.com/calc.php?action=comp

Having looked at all that (with no Lyc. cam specs at hand) I think that the low rpm high torque nature of our engines requires very mild cams with little overlap. For racing/unlimited acro a cam change may be useful. For most of us I don't think so.

I did talk to a guy that had a 0320 built up for acro that had very high compression pistons. He didn't say if the cam was stock. He said that it ran rough below 2500rpm but made lots of power 2500-2900. He had lower compression pistons put in and is much happier with his engine.
 
Something doesn't sound right

This info was originally submitted by Mahlon Russell:

It seems to me that if the bore is the same but the stroke increased to go from an O0320 to an O-360, that the same pistons would give a higher compression ratio with the longer stoke engine. Of course it is possible that due to differences in combustion chamber size, or the distance between the piston crown and combustion chamber, that the compression ratios could work out to be the same with a particular combination of pistons, rods and cylinders, but in general this would not be true.
 
Sure;
Longer stroke would use a shorter connecting rod if the same piston was used; Block deck height and cylinder/head being the same.
 
other considerations

interesting thread and good information from Mahlon on how to achieve certain results.
It is probably obvious to most (but it wasn't to me, hence this post for those like me who might benefit) that engine modifications (and not only to compression ratio) can substantially affect other important choices such as propeller and have consequences to the build.
My experience in building my RV is that decision points arrived when I was not really equipped to make a fully informed decision. As has often been said in various contexts, it is not knowing what we don't know that can create problems.
For example, Van's asks for an engine selection to be made at the time of ordering the finishing kit. I selected a constant speed vertical induction 0-360from the form. I did not know that Van's plans and finish kit did not support that option. Not fatal, and I am happy with the choice I made, but it troubled me that I only figured that out later.
The next point - I ordered an engine. I chose an AeroSport engine, fuel injection, one mag and one Lightspeed. A good engine choice, I think, from a very good engine builder. It was only later, when I needed to decide on and order a propeller, that I discovered that Hartzell, for example, has a list of tested and approved engine/prop combinations that do not include the engine that I ordered (and would not include an engine with high compression pistons, to bring this post back to the thread). After some research and discussions with knowledgable people I have a Hartzell prop and am happy with the choice. But again I found myself having configured the engine without benefit of all the relevant considerations.
So, for anyone like me doing this for the first time and thinking of speed and power mods, like electronic ignitions, porting and polishing, playing with compression ratios, there are considerations down the line other than horsepower and engine performance.
Bill Brooks
Ottawa, Canada
RV-6A finishing kit
 
engine-ering?

Bill,
I feel your pain! Every descision made along the way, whether informed or not, has that dreaded domino effect!
I'd like to know if there is some way to know if, for example, I run 94 octane mogas in my lo-comp 0-320, or the future avgas, what hp I can expect?
perhaps we should be re-doing flight testing, as we would if we installed a 125 hp engine instead!
the new t/off distance over 50' obstacle is..........?? feet
rate of climb at gross is now...........fpm?
etc etc.
 
No "block" per se, but the deck height is not the same

Sure;
Longer stroke would use a shorter connecting rod if the same piston was used; Block deck height and cylinder/head being the same.

Scott,
"Block deck height" is not the same when comparing a 320 to a 360. The 360 cylinder is 0.500" longer to complement the extra .500" of stroke. The easy way to tell a 320 cylinder from a 360 cylinder is to count the fins on the steel barrel. A 320 will have 15, a 360 will have 19.
Charlie Kuss
 
Thanks! I didn't know the combination, just the relationships!
I have an RV-9a project on the back burner waiting for me to finish the RV-8.
So I have to keep my eyes open for the right powerplant choices.
 
cylinder breakage

I talked to Gibson in OK about higher compressions. His take was that it was asking for blown heads. Have there been any issues of cracking associated with higher compressions?

Also, is the LW-15357 9:1 piston applicable to parallel and angle valve engines?
 
Piston Compression & TC E-274

The Type Certificate line of logic is from FAA/FAR's. For review by this panel but found on another GA website.

FAR 1.1 General Definitions? which (as extracted from current FAR?s) states that:
?Major alteration means an alteration not listed in the aircraft, aircraft engine, or propeller specifications--

(1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or
(2) That is not done according to accepted practices or cannot be done by elementary operations.?

And conversely

?Minor alteration means an alteration other than a major alteration. ?

The overarching fact is that the alteration of the engine to type O-320H, to which the minor change will reference as the changed engine, is clearly listed in the governing engine specification control document which is ?Type Certificate Data Sheet No. E-274 Revision 21?, refer Appendix 3

The Type Certificate Data Sheet No. E-274 is the FAA certification document for the 0-320 engine. All engine models listed in the document lie within 0-320 engine specifications. In the TC block on each engine data plate ?274? appears for all 0-320 engines listed in the E-274 document. Revision 20 to E-274 dated August 10, 2009 lists 59 engine models that fall within this engine specification, including 0-320-E2A and 0-320-H3AD.

Therefore converting an ?E2A to a ?H3AD is a change within the engine specification and qualifies as a minor change as all engineering issues were considered when the type certificate was issued, or else a new seperate type certificate would be needed.
 
I care

Reilly,
"Blah Blah doesn't really address the point.
A "major alteration" as defined by the FARS is relevant to what we do. The FARS definition reflects physics and safe practice. We may be exempt from FARS but not from what the FARS are trying to address. We ignore that at our peril. To bring this back somewhat to the thread, changing to high compression pistons, for example, has consequences to things that matter such as suitability of propeller.
Bill Brooks
Ottawa, Canada
RV-6A finishing
 
O-340 Conversion parts

SO I've been reading about the O-340 currently offered by ECI and others.
This is not the O-340 used in the twin Navion, rather, an adaptation of a 4.125" stroke crankshaft, O-320 cylinders and standard 4 cylinder crankcase?
My 'research' indicates that a custom connecting rod might be used?
Stock 5.125" pistons, as used in O-320 & O-360?
Or, is a stock length connecting rod, and a low compression piston used, to result in a higher compression ratio?
What is the parts combination? Can a O-360 crank be offset ground to reduce the stroke, and be reliable?
Any antecdotal stories on custom O-340 engines and their history?
Can an "engine guy" reasonably build his own experimental O-340?
 
Just got back from a visit to LyCon and tour of the facilities. We talked compression quite a bit. Seems 10:1 is almost the minimum/norm there for performance engines. The problem is taking care of it and understanding the cooling issues with need for increased fuel flow for cooling at lower elevations. I'm at sea level so this is a concern and will be researching it carefully.
 
I have an O-320E2A that will be coming up for major overhaul + new cylinders in the not-too-distant future and I'm wondering whether to take the opportunity to increase the compression ratio from 7:1 to 8.5:1, if all it takes is pistons/pins/rings.

I thought the regular 7.5:1 pistons have a flat top surface?

But mine are certainly not flat, I need to get in with a borescope and see what shape they really are.

So then I would wonder what pistons were installed last time this engine was overhauled .....
 
The bump from 150 to 160 hp seems to be one of the most effective and cheap hp increases. If you go over 8.5:1 you pretty much can't use UL fuel anymore. Well worth doing, I think.
 
High compression and LOP

I am interested in running a IO320 with 9:1 compression in my 9A. I plan to use fixed pitch prop set for cruise so the extra power would be nice during takeoff. Also:
a) Does high compression mean I can run the same amount lean of peak with a higher true airspeed? (I guess what I am asking does 50C lean of peak produce more HP with higher compression pistons at altitude?)
I am hoping this will allow me to run up high, LOP, and closer to VNE without having to resort to CS prop.
 
Planning to overhaul my O320-E2A, I'm wondering what pistons are currently in this engine. I was under the impression that 150 HP pistons have a flat top. My piston top faces have two slight semi-circular depressions, presumably corresponding to the valve positions.

I wonder what this tells me - I wonder whether it's possible this engine was last overhauled with nonstandard pistons?
 
Piston / Compression Ratios for Titan "Stroked" engines

Titan Engines by Continental Motors offers all of the compression ratio piston options the Mahlon listed for 320 and 360 cubic inch Titan engines. We also have the following options for our higher cubic inch displacement engines that are the same size and very similar weight to the 320 and 360. The additional displacement (and HP) is accomplished by manufacturing the crankshaft connecting rod throws longer. Other modifications are incorporated to maintain proper clearances within the crankcase. Here is a list of pistons, compression ratios and rated HP for these displacement engines.

340 cubic inch (stroked 320)

AEL75412 8.0:1 +- 175 HP
AEL75413 9.0:1 +- 180 HP

370 cubic inch (stroked 360)

AEL75089 9.6:1 +- 200 HP
AEL75082 8.3:1 +- 187 HP
AEL75413 7.8:1 +- 183 HP

James Ball (J.B.)
P.S. I am an employee of Continental Motors in Mobile AL.
 
This is great, James, thanks! If I'm reading this right, I can swap the AEL75413 pistons for AEL75412 in my Titan O-340 stroker and run premium mogas (91 AKI) if the need ever arises, and only lose 5HP. Does that sound right?
 
Titan Pistons

Yes, the lower compression pistons P/N AEL75412 would be the way to go if you wanted to use mogas.

Aviall is the source for our parts. If you do it, you could transfer the piston rings from one piston to the other and return them to the same cylinder barrels that they are broken in to. Otherwise, there is a service instruction for honing the NiC3 cylinders if that is what you have. That SI is located here;

http://continentalmotors.aero/titan/documentation.aspx
 
I'm reading all of this about Titan engines but are these new Titan engines that Continental now sells different from the Titan engines that ECI sold back in 2008?

I just bought an RV-8 with one of those Titans sold my ECI as a Lycoming 0-360-a1a2n with 75413 pistons. The previous owner used 100LL for take off (left wing tank) then once he was in cruise he switched to the other tank that only had 82 non-ethanol (right wing tank). He has done that since new for over 10 years and 400 hours and says no denotations or different temps noticed.

I can only get 93 octane Non-Ethanol mogas where I live so I'm going to use that. Will I get the same horsepower with 93 mogas as with 100LL?


Since Continental bought ECI, are they the ones to contact to buy parts and to ask questions to about my engine or is another company taking over these engines?
 
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AEL75082 Piston Availability

Titan Engines by Continental Motors offers all of the compression ratio piston options the Mahlon listed for 320 and 360 cubic inch Titan engines. We also have the following options for our higher cubic inch displacement engines that are the same size and very similar weight to the 320 and 360. The additional displacement (and HP) is accomplished by manufacturing the crankshaft connecting rod throws longer. Other modifications are incorporated to maintain proper clearances within the crankcase. Here is a list of pistons, compression ratios and rated HP for these displacement engines.

340 cubic inch (stroked 320)

AEL75412 8.0:1 +- 175 HP
AEL75413 9.0:1 +- 180 HP

370 cubic inch (stroked 360)

AEL75089 9.6:1 +- 200 HP
AEL75082 8.3:1 +- 187 HP
AEL75413 7.8:1 +- 183 HP

James Ball (J.B.)
P.S. I am an employee of Continental Motors in Mobile AL.


Aviall currently shows no stock on AEL75082 pistons. Are these still available?
 
AEL75082 pistons

Yes, they are available. We have them in stock here at the factory in Mobile.
Aviall should request or we should submit that part number into their system. Do you need some ? I can be contacted at 251 436 8122
 
Just a question on octane ratings, I'm assuming the system of measuring octane is the same all around the world. In Australia regular unleaded is 91 with 2 grades higher before you get Avgas. The 2 grades are 95 and 98. That being so could I run 95 or 98 in a high compression 200hp engine?

Kit (rv7) arrives this weekend and engine choice is still a long way off.

Also my first post....
 
Honestly, I didn't even read the article, beyond the essential point that USA mogas is an average of two octane rating methods vs avgas using one of them. Looks like it was basically a commercial for their octane measuring gadget.

I never worry about mogas contamination from the pump, other than checking each batch I buy for alcohol before using it in the plane. I *do* use a water/trash separating funnel when fueling the plane, because I do worry about my own sloppy handling. I can get 93 mon/ron E-free mogas in my area, and I've never had an issue running fresh summer blend in an 8.5-1 compression Lyc. (Winter blend in 100*F summer heat is a story for another day...)
 
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