By Paul McBride · ·
Q: Our flying club is getting ready to have our engine rebuilt and some have asked about upgrading to 180 hp using an STC on the Lycoming O-320. Have there been any issues doing this and does the engine make it to TBO?
We currently have a Ram STC and a Power Flow Tuned Exhaust on it.
Alan Stone
A: Alan, if you do have, in fact, a Lycoming O-320-E2D, you don’t need to go any further as the answer is simple.
To my knowledge, the O-320-E2D was never bumped up to 180 horsepower (legally that I am aware of) because of the front main bearing configuration, which is the same as the Lycoming O-235 series of engines.
If there are any STCs out there, I have no knowledge of them.
However, if there is an FAA STC to make this conversion, I’d strongly recommend you contact someone who has experience with this conversion other than the original STC holder.
With regard to the engine making TBO, I wouldn’t have a clue and the actual service life of the converted engine should come from an operator who has complied with the STC. I have my doubts that this subject would be addressed in the STC.
I’m not certain there is an STC to upgrade the O-320-E2D to even a 160 hp configuration. Again, this would be because of the front main bearing. There are some models of the O-320 series engines that can be modified to increase horsepower, but not the O-320-E2D.
I’m not familiar with the RAM STC you presently have, but not knowing the particulars, you must gain some advantage from it. The Power Flow exhaust system is also an advantage to get more power out of the engine.
We must remember that this O-320-E2D is certified at 150 hp @ 2700 rpm at sea level on a standard day. Once the airframe manufacturer installs its equipment, like the exhaust system, cowling, induction system, vacuum pump, and any other engine driven accessories, these all reduce the total output power of the engine to a horsepower figure that may surprise you if you were to sit down and run the numbers.
Let me offer a suggestion. Not knowing what the RAM STC offers and the efficiency of the Power Flow exhaust system, and the total time on your engine, let’s assume you’ve lost an unknown amount of horsepower. My thinking here is just doing a fresh overhaul on your engine, bringing everything back to factory new limits. You may be surprised at the difference in power and it may improve aircraft performance without spending lots of extra money.
Everyone is always looking for more horsepower and lower fuel consumption, but when it comes right down to it, we must allow logic to creep in and save us.
This brings to mind one more thing and that is there are wants and needs, so ask yourself, do I want this increase in power and am I willing to spend the extra money to get it, or do I really need it for the type of flying I do?
About Paul McBride
Paul McBride, an expert on engines, retired after almost 40 years with Lycoming.
Send your questions to askpaul@generalaviationnews.com.
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RJ W saysThe short answer is no. The right answer is their is no stc, however, you can turn a o320e2d into a 180 hp quite easily. Ly-Con has a video on their website running an o-320e2d with 160 hp stc with ported and flow matched cylinder heads in an engine test cell with straight pipes. They show 180-185 hp 2600-2675 rpm on the engine test stand. With the power-flow exhaust and an electroair electronic ignition, you should get some where in the mid-high 170’s actual shaft h p at the crack shaft. Keep in mind the o-320 is 15-20# lighter than a 0-360. Having this done and having the engine and prop balanced is really the hot set-up for the Cessna 172 and I will be doing this to my C-172. RJW!!!
- Daniel Barbee says
Penn Yan Aero has an STC to overhaul and convert the O-360-E2D to a O-360-A4M 180 HP called the Super Hawk. I checked into it several years ago when I had a 1976 C172M but don’t recall the price.
https://www.pennyanaero.com/superHawkPage
My 172M’s O-360-E2D had the RAM STC to increase HP from 150 to 160. The STC included new cylinders, pistons, wrist pins, and carburetor and required re-pitching the propeller. The STC is designed to be installed during an overhaul and primarily intended to allow the engine to burn 100 octane fuel. Maximum power is limited to 5-minutes takeoff power. Mine was installed by Penn Yan Aero during the previous overhaul.
RAM also offers a “Maximum Power STC Package” STC that removes the 5-minute limitation.
http://www.ramaircraft.com/Aircraft-Parts/RAM-STCs/172-upgrade.htm
- Cary Alburn says
Just speaking in generalities because I’m not a mechanic, but whenever you take an engine that is designed for a certain horsepower output and convert it (hot rod it) by whatever means, you risk over-stressing it. It will at the least cost you more in fuel consumption. That is not to say that a small engine can’t be created that puts out more power than a larger engine and also gets better mileage. That has happened throughout the automotive world, but those engines have been designed from the beginning to put out more power in spite of their small displacement, while getting better mileage.
For aviation purposes, if you want substantially more power, it’s better to go for a bigger engine than to convert a smaller engine to put out more power. Sure, there may have to be baffle and cowl changes, but those are relatively inexpensive compared to modifying an engine just so that it will still be the same physical size.
Finally, you have to ask what you expect to accomplish. Adding power to any Cessna won’t turn it into something that will fly at Mooney speeds. I own a 180hp O-360 Lycoming powered 63 P172D, with the engine mildly tweaked to the extent allowed for certified engines, so that it puts out as much power as possible. I also have a CS prop. The combination definitely gives my airplane better acceleration and climb capabilities than a stock 172 of the era that had only 145 hp. It also goes a little faster; 115 knots is what I use on flight plans, and it works pretty well. It’s also capable of operating at higher altitudes than a stock 172. But by no means is it a fast airplane.
So my advice is, if you want to keep the costs reasonable, overhaul what you have. If you really want more power, get a bigger engine. Don’t tweak your smaller engine, because in the long run, your club’s wallet will regret it. And don’t delude yourselves into thinking that more power will substantially increase your airplane’s capabilities.
- Manny Puerta says
Agree with above comments.
As as option, a friend with a C-150 at a 4700’ MSL airport installed electronic ignition. Because of it’s ignition advance curve characteristics below 24-25” MAP it performs noticeably better in climb and cruise.
It certainly made a difference in my 185 along with flap gap seals. Better climb rate, faster cruise and less fuel burn. Can’t be anymore expensive than engine mods.
- Larry says
The low compression 150hp O-320 engines DO have an STC to convert them to the higher compression 160 hp level. Several outfits have an STC. I have NEVER heard of an O-320 being STC’ed up to 180hp, as Paul says. Even the up conversion to 160hp can be a shaky conversion because the O-320 “D” (high compression) engines have heavier duty crank case halves. Converting the lighter duty 150hp “E” crankcases is impossible. The power pulses created by the higher compression top end is being absorbed by the 150hp crankcase halves. I do know of a few people who did that conversion and have not heard of problems, however.
For myself, when my O-320-E2D engine was ‘due,’ I bought a factory new O-320-D3G 160hp and converted it to D2G configuration (7/16″ prop bolt bushings in the crank). The additional 10hp plus the requirement to repitch the prop to 57″ from 53″ made a huge performance improvement. Four inches of pitch in a perfect fluid is 9.3mph at 100% efficiency and that’s about what I see over the 150hp engine. Before making that choice, I rented a C172 with a 180 conversion and didn’t see the point of a major mod of the engine bay sheet metal because that engine is larger. I am VERY happy with the 160hp and would do it again. The beauty is that I didn’t have to modify my baffling or anything and the SFC is almost the same … possibly better because of increase prop pitch?
- Marc Rodstein says
I met Paul McBride nearly 50 years ago when I took my Mooney to the Lycoming factory to have a top overhaul done. I have followed Paul’s writings and am always impressed with his knowledge, but I have to disagree with his comment about power increase on a freshly overhauled engine. I have overhauled or exchanged for overhaul three different Lycoming engines and I never noticed any increase in power after the overhaul. If the run out engine was operating properly, you should not expect an increase in power or performance when replacing or overhauling it.
- Mike says
I have always liked your articles, but I have an alternative logic in respect to part of this article:
“just doing a fresh overhaul on your engine, bringing everything back to factory new limits. You may be surprised at the difference in power and it may improve aircraft performance”.
I partly disagree. Though this may happen, the engine may not have been airworthy to begin with. Let me explain.
Different manufacturers have different specifications on engine output, just like you said, with or without accessories. But each engine and airframe combination is different. Some have a power rating of some value +X% -0%. Some have a range over or below the rating. However, part of their type criteria is that if they are maintained in accordance with manufacturers maintenance instructions and are found to be airworthy, then they should make at least minimum rated power, otherwise, pilots could potentially get into trouble. Could you imagine the lawsuits if it was proven that an accident was caused by the engine not making rated power, when it was actually deemed airworthy in accordance with manufacturers instructions? Whoa, it would be a feeding frenzy.
If engine wear and time in service actually had any negative impact on aircraft performance, one would think that part of the performance section of the POH would have included a table for engine time? There are performance tables for everything else, grass vs pavement, density altitude, uphill vs down hill, tail wind vs head wind, but there has never been a section for engine time. There probably never will, and there doesn’t need to be such a table.
This is because if they have been maintained properly (according to approved data) then they should make rated power, regardless of time in service up to its recommended TBO. It can actually make rated power beyond TBO, if it still meets its original airworthiness criteria, its just not recommended. But lets be real, that does not imply risk, otherwise, it would be mandatory, not recommended.
Also, this is one of the many reasons, we might consider NOT running engines past TBO. Part of the recommended instructions wherein airworthiness limitations are relevant are outlined in the data, which includes, but is not limited to recommended TBO, which also includes a recommended calendar life, I think it was 12 years in the case of Lycoming, for example. There are also service bulletins, instructions and letters (depending on the brand) that most ignore, however are very important. Why would the factory waste the time to publish such information if it were deemed irrelevant? Most think its to force the customer into buying something, or covering their backsides from potential litigation, though sometimes this could be the case, but not always. The majority of the time, field service information identifies potential problems, that after carefully vetted, should be addressed in some way or another.
So to add to your great article, if a customer has his engine overhauled, and performance dramatically increases, then there was a more serious problem to begin with, and prior to overhaul, the engine was not actually airworthy.
Years ago a test at Continental was published (I think it was TBO advisor) wherein piston rings were actually removed from the piston for a dyno test, to prove that the leak down rate from blow by (aka “compression”) had little to do with engine performance. The engine smoked like a train, but it did make rated power. Today, compression tests are much more prescriptive, which includes the use of a master orifice tool and borescope inspection. Further proof that we have improved safety with more prescriptive maintenance instructions. This actually saves us all time and money and unnecessary cylinder replacement, only to do it over and over again over the life of the engine.
