Airworx 180HP O-300 STC

[ghostflyer]

I have written in the past about modifying the continental engine O-300 and have now come to the conclusion is that it’s safer and more reliable to leave it factory standard. However we did find some of the castings very crude. The intake plenum chamber was polished out including the cylinders intake and exhaust ports. I think it was No.5 piston /cylinder always seem to run rich in comparison to the other cylinders , this issue went away after polishing. I now wish in the beginning we had just put a bigger and more powerful engine in and not wasted our money.
In my humble opinion and a little what i know Continental tried to develop this engine but decided in 1964 to develop a clean sheet IO-360 engine . which produces between 180-220 hp .

[akahrs757]

Was this in relation to the airworx work? Or was it a normal overhaul?

[ghostflyer]

This is where I had the bright idea of extracting more power out of a O-300. This was done nearly 20 years ago. I was friendly with a tech rep from Continental and having many discussions with him and some of his colleagues . I thought a change was a good idea. My engine needed a top overhaul at that time and it seemed a good opportunity to “improve” it. The castings were shocking and very rough. No 5 cylinder was very rich all the time and the casting condition in the plenum chamber was shocking . We acquired new pistons /rings , and cam shalf and cam followers. The intake and exhaust ports were polished and slightly modified in shape. The first hours on the dyno ,the oil temp was very cold but when fitted to the aircraft it was very hard to control ,it over temperature all the time . To cut a long story short ,I would never try to modify a O-300 engine . The amount of money and time spent ,not worth it. Plus I had to put my aircraft in a temporary cat of experimental. In its present design ,the O-300 is a bullet proof and reliable engine . It’s my belief that continental , RR and Rutan tried to modify the O-300 design concept and failed. There was a LuLO-300 engine
[water cooled] and that had cooling issues. If you want more power and grunt get another type engine . eg Bird dog — similar to the 170 but totally different engine .

[abushey123]

To the previous question on reliability of increased horse power o300. I have run a o300d with cylinder port and polish, sump port and polish, an adapter to run a ma4spa carb to allow a bit more airflow, 10:1, and advanced timing for almost 1000 hours. The only things to note is harder starting due to higher compression and using a carbon propeller, higher CHT (425f) on long hard pulls and a slight increase in oil burn. The largest gain I noticed was from using the original o300d cam and NOT the superior or new Continental cam as the profile does not allow rpm to pass 2700. The current setup allows for 2825 on takeoff using a 86” sterna. With a stock wing, 31” bushwheels on a standard day 29.92 and 15 deg at sea level to about 2000 feet I could constantly climb around 1500-1600fpm at 70 mph. This was shown on both an VSI and GPS. Empty weight of 1270 and takeoff weight of 1700ish lbs. The compressions were great all the way to removal of the engine and I never had any abnormal metal in the screen during changes. Engine had 1700 hours at the time of removal.

[n2582d]

I just sent an email to Airworx regarding the O-300 modification. Apparently they will not be pursuing an STC, but will modify the engine under a 337. Here’s the information I received:

Just for the sake of information: we will not be pushing forward with an STC package. HOWEVER! We do have authorization to modify each engine individually. At the end of your overhaul, you would be getting a certified engine with a 337 for major alteration. I've seen a few things floating around the internet, but the paperwork is written to be 170 hp, at 8.5:1 compression ratio and a slight increase to the jetting on the carb. If you have any questions feel free to reach out.

Here’s a recent update from Airworx:

UPDATE ON THE CONTINENTAL O-300 SERIES 170HP CONVERSION
We have paused the 170 HP engine conversions while a full STC is being developed and approved. We anticipate this being completed within 4-6 months as we are going with an ODA as the approving authority. This will allow not only us to build your engines but will also open up the possibility of upgrade in the field by other shops or mechanics. We had been doing this as a major alteration using an engineering order but have been advised to do them with an STC approval instead.

I’ve never heard the term ODA before. Apparently it stands for “Organization Designation Authorization.” Here’s a link to an FAA website describing it.

[GAHorn]

…. Here’s a recent update from Airworx:

UPDATE ON THE CONTINENTAL O-300 SERIES 170HP CONVERSION
We have paused the 170 HP engine conversions while a full STC is being developed and approved. We anticipate this being completed within 4-6 months as we are going with an ODA as the approving authority. This will allow not only us to build your engines but will also open up the possibility of upgrade in the field by other shops or mechanics. We had been doing this as a major alteration using an engineering order but have been advised to do them with an STC approval instead.

I’ve never heard the term ODA before. Apparently it stands for “Organization Designation Authorization.” Here’s a link to an FAA website describing it.

Resurrecting an old thread…. I keep receiving queries about engine overhauls and “ugrades”…. and I am on-record as a skeptic on anyone’s marketing claims to “increase HP” on these C145/O300 engines. (Before one can claim to “increase” the OEM, one has to have a “control” engine for comparison. It’s not valid to compare a rebuild-engine with production-engines mfr’d decades ago that were only claiming to meet minimum certificated standards, and that any engines which TCM made that could exceed those minimums were not mentioned. (Hint: I will almost guarantee that each-and-every O300 exceeded 145 hp because TCM couldn’t risk an engine going out the door that failed to meet certification output.)

The latest query has come in this last week (Feb ‘26) with a claim by a well-known shop already mentioned ….that claims to port/polish and spit-shine this engine until it put out “increased HP on their dyno” …and they offer to show the test data on the engine you’ve submitted to them “proving” their claim….so you will select their shop for your engine-work.

I wish to point out that the original mfr’r (OEM) of this engine, TCM, met FAA and other OEM’s requirements when they gained Approval for 145 HP at 2700 RPM. (and upon-which airframe mfr’s relied when building airplanes to meet FAA performance certification….which this shop’s engines will not be required to be re-certified-for.)

TCM, in order to gain that Approval…had to mfr All subsequent engines to meet that minimum standard. WE Understand…don’t we…,, that “meeting” a standard …is a “MINIMUM STANDARD” ?? In other words, Each and Every O300 coming off the TCM line had to be capable of producing 145 HP @ 2700 RPM under the standard conditions. They did not get to claim any addt’l HP produced… despite the certainty they all did so.
So…if any particular engine was capable of making 150 HP…or 170 HP…or ??? …… NO Additional HP output needed to be documented…. or claimed…or advertised…. or even tested-for, (in fact, if such a claim were made by TCM they would have had to go-thru all that recertification all over again.)
In Other Words: The 145 HP O300 engine met a miniimum…and is therefore eligible fo installation. (and “minimum” in this context is Not a bad thing)

If John Hicky-Doo opens an engine shop and turns out a rebuilt engine and puts it on John Hicky-Doo’s “dyno” and says that he held his tongue in his left-cheek on a Thrusday Evening and “the dyno” ….”PROVED”…. that engine put out 170 HP….. does that mean the technique he used holding his tongue makes John Hicky-Doo’s engines Better than TCM’s ??

In fact, TCM had to show that their engine produced that 145 HP throughout the life of that engine until TBO. I don’t know if Hicky-Doo’s 170 hp engine will continue to make 170 after it was taken off the “dyno”.

(I know folks who turn their exhaust tailpipes around-back-ward so the scarf-cut at the exit-point on them doesn’t fight the relative-wind preventing their engine from making maximum output. I wonder if FAA would allow an “ODA” to make a claim on their own “approval” of themselves…
I wonder how many remember when McDonnell-Douglas had ODA to approve their own cargo-door-latches on the DC-10…

[n2582d]

... In fact, TCM had to show that their engine produced that 145 HP throughout the life of that engine until TBO. ...

Where did you find this George? I haven't researched this in depth, but it appears the O-300 was certified under CAR 13. The longest endurance test I find there are 150 hour tests which even allow for minor repairs during this test.

[GAHorn]

I didn’t “find” it. I derived that from the Type Certificate and Mx approvals from CAA/FAA which require the certification you mention, and also require and approve on-going maintenance / repair schemes which keep the product within design specifications.

These (and other) engines have “recommended” TBO’s (mandatory when in Pt 135 service, etc) and undergo regular inspections and tests to assure they continue to meet their specified performance. When they no longer meet that standard they are required to be removed from service and/or the TBO recommendation / requirement is determined. (Can be extended when the mfr’r establishes that capability over a certain percentage of the fleet.)

Subsequent STC-developers only have to show their modified product does not diminish safety or reliability. Holding an engine STC is a separate matter…and does not make the marketing claims of “improvement” valid. (I.E. the STC does not validate the increased HP claim. It only allows the installation of the modified engine to be installed on a type certificated airplane.)

[DaveF]

Subsequent STC-developers only have to show their modified product does not diminish safety or reliability. Holding an engine STC is a separate matter…and does not make the marketing claims of “improvement” valid. (I.E. the STC does not validate the increased HP claim. It only allows the installation of the modified engine to be installed on a type certificated airplane.)

Ah, you finally got to your real beef: engine upgrades.

[GAHorn]

Subsequent STC-developers only have to show their modified product does not diminish safety or reliability. Holding an engine STC is a separate matter…and does not make the marketing claims of “improvement” valid. (I.E. the STC does not validate the increased HP claim. It only allows the installation of the modified engine to be installed on a type certificated airplane.)

Ah, you finally got to your real beef: engine upgrades.

I have no “beef” with engine “upgrades”.

I’m not deriding this or any other STC holder or mfr’r. My comments are intended to lend a realistic view of marketing claims.

(I believe that in-order to make the claim valid…. the STC-holder would have to show the engine WITHOUT the modification was incapable of making claimed enhancements…. And also show that Only Their Modification is what enabled improvements, if any.)

The TCM engine HP output is a “Minimum” claimed output. Each/Every engine which comes off the assy-line meets that “minumum” …in order for the airframe mfr’r to rely upon it for meeting the airframe certification standards.
(I.E. there Is No physical or mechanical “limiter” to preent a new O300 from producing more than 145 HP. In fact, that is supported by the fact that TCM even publishes data to show at what RPM that minimum rating is achieved. If they claimed More HP… then the airframe mfr’r wold have to alter Their data as well… All of which would toss the certifications out the window.)
If I were an engine mfr’r…or RE-mfr’r… and wanted to Lye …. or Con someone into buying My product instead of anothers …. I’d simply take a new off-the-line or reconditioned O300 … spray some magic-dust of my own design upon it…and put it on my dyno and show that it exceeded the Minimum-Claim made by TCM…(which we all now know is a Minimum that All their engines Must.)

[n2582d]

If John Hicky-Doo opens an engine shop and turns out a rebuilt engine and puts it on John Hicky-Doo’s “dyno” and says that he held his tongue in his left-cheek on a Thrusday Evening and “the dyno” ….”PROVED”…. that engine put out 170 HP….. does that mean the technique he used holding his tongue makes John Hicky-Doo’s engines Better than TCM’s ??

In fact, TCM had to show that their engine produced that 145 HP throughout the life of that engine until TBO. I don’t know if Hicky-Doo’s 170 hp engine will continue to make 170 after it was taken off the “dyno”.

I’m not deriding this or any other STC holder or mfr’r.

John Hicky-Doo? When "dyno" is put in quotation marks it certainly gives one the impression that the results are not to be trusted and, by extension, the company is deceptive.

Chris, the COO at Airworx, wrote,

I can tell you that a worn out engine doesn’t make 145hp. More like around 138 depending on climate conditions on a given day.

We have tested a stock engine (145 hp) right after overhaul I got 147 HP. We tested one of our high compression engines the same day with the same dyno and same climate conditions and got 174 HP.

When an owner spends tens of thousands of dollars modifying their plane's engine or airframe, to rationalize such spending, they will tend to see performance improvements that may be real or a chimera. So, while I agree it would be best to dyno test the same engine before and after this modification, I seriously doubt that one will find a stock 1500 hr. or freshly overhauled O-300 cranking out anything close to 170 hp. That much of a horsepower increase cannot be a figment of imagination.

[GAHorn]

…
John Hicky-Doo? When "dyno" is put in quotation marks it certainly gives one the impression that the results are not to be trusted and, by extension, the company is deceptive.
.

Are you familiar with the make, model, and type or age of John’s “dyno”….and do you know if it meets any standard of performance by any recognized authority..? Do you know if it has been recently calibrated or tested to meet that standard?

When I place “Dyno” in quotes…. it was deliberately done to point out that the claims of marketers don’t / shouldn’t carry automatic credibility. The word “dyno” might be convincing to those gullible folks who might be mesmerized by the term…. but is meaningless assumption without a “standard”.
One must have faith or trust in the claimant or the company reputation to believe any testing results on some “dyno”.

If you don’t know John Hickey-Doo… or the specifics of the test-comparisons of the two engines…. then his claims would be unconvincing without authoritative collaboration or other support.

I don’t know how 138 hp was determined…. sounds like estimation or conjecture … (no intent to disparage Cris or Airworx. I don’t know either.) Just sayin’.
Does the STC make or gurantee a specific claim to 170 HP..? or does it only provide approval for polishing and certain “treatment” of various components which the OEM did not specify in the OEM manuals.? That answer would be more convincing, IMO.

[DaveF]

You ask a lot of questions but haven't bothered to talk to AIrworx to get answers. Maybe we should ask the Association's parts and maintenance advisor to do that.

[GAHorn]

You ask a lot of questions but haven't bothered to talk to AIrworx to get answers. Maybe we should ask the Association's parts and maintenance advisor to do that.

There’s no reason to try to personalize this.

I wasn’t asking questions because I was confused about this. I was posing them as a person might have a discussion about STC claims by STC holders. (If the STC doesn’t “certify” the performance claims…then they’re only a “claim”.)

My remarks are not seeking answers from the STC-holder, nor (as I’ve stated repeatedly) to cast dispersion on anyone. They were intended to inspire a perspective of reality and truthfulness to those who have experienced advertising and marketing claims of “improvements” to originally-certificated products which have met certified standards of production. The onus of proof is not mine to make.

If it were, I’d consider taking a freshly-produced engine from the OEM and running it in a calibrated dyno meter to determine output…. then apply the modifications to that same engine…and re-test it in that same “dyno”…and publish the results, along with commentary of the OEM regarding that modification.

BTW, Airwox, LLC it should be noted that they have a website and have every sign of a quality engine shop. I have no personal experience with them so, don’t think I’m trashing them: https://airworxaviation.com/

[ghostflyer]

Well after rubbishing the concept of “Modernising the Continental O-300 engine I have just seen a O-300 engine fitted to a French rallie with a header[extractor] type exhaust. It has 2 extractor type pipes each side .
The owner explained that parts were impossible to procure and that included the exhausts . So he built his own . Obtained an engineering order from the authorities . It was a beautiful job done ,but had no mufflers but a heater muff externally attach to one of the exhaust pipes for carby heat only.
We did only 2 circuit patterns not enough for a in-depth appraisal . The noise factor was increased greatly BUT the engine revved lot quicker and had an interesting “after fire “ when the throttle was reduced quickly. The engine appeared to rev quicker . Maybe a small edge on power .
His claim .. fuel economy has a small improvement. It’s sounds “mean”. I just think that Douglas is a rev head and hasn’t left his teen age years.
PS. we do not need a cabin heater here in Australia , I think I have used mine once in 20 years .