I was talking to a local who’s also got a 170. He has the O-300 off for overhaul. He said that he’s contemplating selling the fresh 300 and installing a 180hp and having it field approved. We were talking about the cost involved with say a Stoots conversion etc. He exclaimed that you can bypass all of that with a field approval. I don’t think that anything he said is correct. I wasn’t going to argue about it though. There’s no way they would field approve the 180hp conversion would they? At least I’ve never heard of it being pulled off.

In the old days he was right, you could get a field approval for something that was also STC'd.

Today I believe the unofficial word at most FSDOs is they won't field approve something that an STC exists for. That being said, I don't think this is official, and if it is the inspector has to know the STC exists. They do this to avoid taking money out of the STC holder's pocket. If there is a FSDO issuing FA's on the same inspection panels or a cargo pod that I own an STC for, then I am in competition with uncle sam.

This is all contingent on the inspector knowing about the STC. I don't think they are digging through looking for it. I also don't believe this is official policy as I've never seen anything written but I've never looked either. I've just had a couple inspectors tell me this.

My experience mirrors above when Hartzell told me to go get a field approval for the wrong prop they sent me.

I heard about a TCM IO-360 being field approved last year but I have no way to confirm that.
There is nothing officially written that says you CAN'T get an engine swap field approved but the odds are very against.
You need more than one FAA person willing to help you. This will be a serious challenge.
You need your own engineering data for the mount, baffles, cowling changes. This will be more expensive and time consuming than you can believe. Talk to a DER about estimated costs. Or a few DERs as you'll need Airframe and Powerplant DERs for an engine swap.
You need cooling tests. Just developing the test plan for approval will frustrate the bejesus out of you.
I think you'd quickly come to the conclusion that $15 or $20k for everything delivered to your doorstep with an STC bow tied around it is the most cost effective and least time consuming path.

This is one case where build vs buy leans heavily towards favoring the Buy option.

I can't remember where I read it, but it was recently. Basically any HP increases and the FSDO will require an STC, no FAs.

The hassle of getting a field approval would be far greater than just getting the STC from Bob Williams for $1,200.

Newbizor wrote:The hassle of getting a field approval would be far greater than just getting the STC from Bob Williams for $1,200.

Who is Bob Williams and what is he selling exactly for $1,200?

Bagarre wrote:

Newbizor wrote:The hassle of getting a field approval would be far greater than just getting the STC from Bob Williams for $1,200.

Who is Bob Williams and what is he selling exactly for $1,200?

Yes.... what is this $1200 STC? Haha.

The FAA policy is clear that if there exists an STC for what you propose, they will not field approve it.

And, even if you chose to install an engine that's not approved on an STC, as others have noted, you're going to spend a HUGE amount of money, and probably wind up having to develop an STC of your own.

Williams is the guy who owns the Avcon STC, I believe. All you'll get is paper for that.

MTV

$1750 now

daedaluscan wrote:$1750 now

Still worth it, rather than reinventing the wheel.

Anyone who has an Avcon conversion (like I do) knows that it is an excellent conversion, but any mechanic who has done the work is likely to mimic one of our mechanics in Laramie years ago, who was in the midst at the time of doing an Avcon conversion on a 170: "I will never, NEVER do another one of these!!!"

Cary

I'm shooting off a comment way into left field here....but I seem to have read that someone was working on getting either the Titan 340 or maybe it was the O-370 STC'd for the 172/170. It was a while ago that I read it and really haven't looked into it since. Wonder what ever became of it?

WWhunter wrote:I'm shooting off a comment way into left field here....but I seem to have read that someone was working on getting either the Titan 340 or maybe it was the O-370 STC'd for the 172/170. It was a while ago that I read it and really haven't looked into it since. Wonder what ever became of it?

Dave Stoots has the approvals

MTV

WWhunter wrote:I'm shooting off a comment way into left field here....but I seem to have read that someone was working on getting either the Titan 340 or maybe it was the O-370 STC'd for the 172/170. It was a while ago that I read it and really haven't looked into it since. Wonder what ever became of it?

I've now seen two 170b's with the o370 up here. Stoots' display plane and then Mark Hasners. Both look awesome.

Dave now has the IO-390 STC’d

STC SA02343AK FAA Approved for the New IO-390A3A6 210 hp Lycoming

akgreg wrote:Dave now has the IO-390 STC’d

STC SA02343AK FAA Approved for the New IO-390A3A6 210 hp Lycoming

That would be a real barn burner. My 180 hp Lycoming conversion makes my airplane get up and move (well, climb well--cruise is only 115 knots). An extra 30 hp would be pretty phenomenal, and I'd trust a Lycoming longer than I would the similar hp Franklin conversion.

Cary

Airfoil92 wrote:

Bagarre wrote:

Newbizor wrote:The hassle of getting a field approval would be far greater than just getting the STC from Bob Williams for $1,200.

Who is Bob Williams and what is he selling exactly for $1,200?

Yes.... what is this $1200 STC? Haha.

Bob Williams is the owner of the Bush and Avcon O-360 conversion STC's. There is no longer any parts support for them but he still sells the drawings. I bought my set last fall for $1200, but apparently he raised his prices a little and is now charging a little more. He has been replying at [email protected].

Cary wrote:

daedaluscan wrote:$1750 now

Still worth it, rather than reinventing the wheel.

Anyone who has an Avcon conversion (like I do) knows that it is an excellent conversion, but any mechanic who has done the work is likely to mimic one of our mechanics in Laramie years ago, who was in the midst at the time of doing an Avcon conversion on a 170: "I will never, NEVER do another one of these!!!"

Cary

You sure are right it is worth it! I did my conversion last fall, did it all myself and it was very straight forward and actually quite easy. Mechanically its no different than any other 0-360 conversion out there, bolting the mount/engine in place and installing the new control cables. The most time consuming part is building the baffling, which will have to be done for any conversion. Or pre-built baffling could be purchased but I was happy to build my own and save the cash. lastly the cowl modifications which are pretty easy on a 175, probably got about 5-7 hours in to the cowling mods which consists of locating and opening up a new exhaust exit, plugging the original exits, then trimming the top cowl to clear the ring gear on the O-360.

The only parts that proved difficult to procure were the engine mount and airbox, but if I had to do it again I think I would go a different route and that would not be so much of an issue.

I wouldn't hesitate to do the Bush/Avcon conversion again, just have to go into it knowing there is no support from the STC holder and some common sense will need to be used on the install. Substituting or owner producing some bits and pieces when needed like fuel pump (if installed) and voltage regulator, no big deal since there are many options for approved substitutions. I did my conversion for $20K, which included a CGR-30P engine monitor and I know I could do it again.

I have the Williams STC for my 170 and now looking for the air box. Where did you find yours and what would you do different now?

The Landing gear Works has one for a Continental IO 360, 210 HP.

https://tlgw.aero/xpmods