Did the engine builder put those bootleg pistons in the logbook entry or parts list?
If he did that on a certified engine, he's not too bright IMHO.
If this mod is undocumented, are you sure it's even been done?
I know a guy who bought a 172, he was told "we put in the 160hp pistons but didn't put them in the logbook".
That's a legal upgrade to the Lyc 320, I think they were feeding him a line of BS, and guess what....he bought it.

If that mod is undocumented, other than word of mouth,
I wouldn't worry about how it effects the resale value or insurance claims.

hotrod180 wrote:I know a guy who bought a 172, he was told "we put in the 160hp pistons but didn't put them in the logbook".
That's a legal upgrade to the Lyc 320, I think they were feeding him a line of BS, and guess what....he bought it.

Yes, but it depends. As you probably know, there's a wide and narrow deck version of the 320. You can't just put the 160 pistons is a narrow deck cylinder, at least legally. It has to have the hold-down plates on the flange and the through studs have to be long enough to extend past the hold-down plates. If they don't, it's something that can only be installed with the case split.

hotrod180 wrote:If that mod is undocumented, other than word of mouth,
I wouldn't worry about how it effects the resale value or insurance claims.

What if the FAA, or worse the NTSB, investigates if there is some engine issue that contributes to aircraft damage? Do they ever inspect the engine?

If you have a engine failure in flight and IF the NTSB gets involved they will most likely want to look at the engine. Your run of the mill pilot induced metal bending they have no reason to look at the engine.
DENNY

Zzz wrote:

hotrod180 wrote:I know a guy who bought a 172, he was told "we put in the 160hp pistons but didn't put them in the logbook".
That's a legal upgrade to the Lyc 320, I think they were feeding him a line of BS, and guess what....he bought it.

Yes, but it depends. As you probably know, there's a wide and narrow deck version of the 320. You can't just put the 160 pistons is a narrow deck cylinder, at least legally. It has to have the hold-down plates on the flange and the through studs have to be long enough to extend past the hold-down plates. If they don't, it's something that can only be installed with the case split.....

I know about adding the banana plates. I wouldnt want one w/ 160 pistons but without the banana plates. Plus the alleged 160 mod was done at overhaul. The story just didnt add up IMHO.

So exactly what pistons are used for the little hop up, part number etc.

Mapleflt

So exactly what pistons are used for the little hop up, part number etc.I'm planning a "top overhaul" in the not to distant future

Mapleflt

Going from a CR of 6.3 to 7 will yield on the order of 5% more HP. It will also push cylinder pressures from ~630 psi to ~700 psi. The combustion temps will also rise around 11% (the reason for the gain in efficiency, actually). The brake mean effective pressure increase tracks the engine efficiency, and the power of course tracks the BMEP.

Is it really worth it? I doubt it makes a huge difference unless it also requires hi octane fuel to feed it (a negative).

As mentioned, the RPM and stroke changes rapidly move the needle in engine output faster than compression ration changes, but with risks or consequences just as unique as those associated with compression ratio changes. Heat rate is heat rate.

As for comparing a higher compression engine to a "tired old engine", properly maintained engines with a lot of hours on them make the same or more power than factory new engines until the new engines are slightly worn in. There is no magical fairy dust that makes a factory new engine produce more power than a well maintained TBO engine. I've never flown behind a new engine to see any measurable performance increase from the older, timed out but well maintained engine. I've flown behind tired engines that were sludged up, had clogged filters, sketchy mags, or leaky fuel injectors that impacted performance in very noticeable ways, however, and when those items were fixed, the engine was just as boring as a new, freshly broken in engine. I never really understood what people meant when they said "...yeah and holy cow, with that new engine, she really climbs like a homesick angel...". It was something often said that I figured I'd get the chance to see for myself one day, and here I am a few decades later and ...nope. Vibration, you bet. Even well maintained older engines can get sludge and piston crown buildups that contribute to that. But power? Hmm.

In any case, I've never heard of someone turning down the opportunity to try out a hot (if not legal) mod on a plane purchase. Mysteriously, I never really hear them extol the virtues of all that port polishing, high CR pistons, and super duper mods after a while. It all looked so enticing in the features list on Barnstormer. I have heard several grouse about how their core was rejected when they got a rebuilt stock engine swapped, or how MX challenges have left them scratching their heads if it was a good trade or not. In terms of functionality, the 5% increase in power will be about exactly like taking off or climbing at a density altitude about 1500 feet lower than usual. Maybe that is interesting, maybe not.

Good luck with your new ship if you get it though!

Zzz wrote:

denalipilot wrote:I don't know but I have to imagine this would also torpedo an insurance claim if it was discovered.
-DP

Has anyone ever heard of a claim being denied for an unapproved mod, even if the bent metal had nothing to do with the mod?

I asked my insurance agent this question a few years ago. She looked at my policy and said there was nothing in it that required my airplane to be airworthy to qualify for coverage. I specifically asked about undocumented and unapproved modifications or installations and she said it didn’t matter, I would be covered. Even said the plane didn’t need to have a current annual inspection.


Lycon has a link on their website to their high compression forged pistons. Personally I think they are overpriced and still using 1920 tractor technology. There are several custom piston manufacturers that you can send a factory piston to the they will build you a modern equivalent for about a third the price of a factory piston.

100 octane should not be required for 7-1 or even 8.5-1 compression pistons. Depending on what chart you read 91 octane mogas should do the trick.
DENNY

I would get your IA who is going to sign off the annual tell you what he wants to put his name on.

I know plenty of guys running them. Love the extra HP. I don't think that comes without a price. Talk to some more of the experts.