Lower compression CC340?

[JHawkins]

Hi all,

I'm currently awaiting my kit, with a March 21st delivery date. It'll be my first kit!


One issue on my mind - I can't help but think that a lot of the longevity / roughness issues with the CC340 seem to stem from the high compression - (I know it's a complex topic, I'm generalizing)

Has anyone convinced CC to deliver their CC340 with 8:1 pistons instead of 9:1? If so, how'd it work out?

Titan specs on the X340 with 8:1 is 174 peak HP. I'd sure be interested in trading 6 hp for a smoother, more well cooled engine and the ability to use mogas when conditions allow.

I inquired with the dealer when I ordered, but haven't really started digging...

[Dan L]

I believe that when AeroSport was building these engines for CC that was an option. When I bought mine in 2010 I inquired about 10:1s and that was an option but there was no warranty with the engine…….

Unless you plan to burn a lot of car gas I’d stay with the 9:1 pistons. I have added 93 e-free to my tanks when 100 LL wasn’t available. But with half tanks or so of 100LL it is very diluted. I have not had cooling issues with my O-340. I did have a burnt valve but I don’t think the compression caused that. More likely operator error..

[ceslaw]

With Santa Clara County, California, banning leaded fuel at two significant airports effective January 1, and concerns that similar bans will be popping up across the country in certain locations, the issue is heating up.

From what I can tell, dropping the compression from 9:1 to 8.5:1 will not, by itself, prevent detonation. Need to do other things, like changing the timing. Way beyond my pay grade. Sure hope a solution presents itself soon.

[ptredway]

Sure hope a solution presents itself soon.

Been following any of the G100UL news?

https://youtu.be/UvJ4vjtmWY8

As of a few weeks ago, FAA approved for something like 80% of the engines in the fleet. Didn’t see any of the 550’s on the list, but those and any other missing are expected soon.

I’d anticipate Santa Clara and other localities to follow will be pushing to stock the tanks with this stuff.

[ceslaw]

Been following any of the G100UL news?

https://youtu.be/UvJ4vjtmWY8

As of a few weeks ago, FAA approved for something like 80% of the engines in the fleet. Didn’t see any of the 550’s on the list, but those and any other missing are expected soon.

I’d anticipate Santa Clara and other localities to follow will be pushing to stock the tanks with this stuff.

That is definitely encouraging.

[jamiller]

In light of the constant lip-flapping about 100LL going away, when I ordered my CC-340 in 2015 I spec’d 8.5:1 CR so Mogas would at least be an option. At that time the engines were being assembled by Aerosport with parts from ECI, CC & who knows where else. They supplied the engine with a different timing ring appropriate to the lower compression and made whatever modifications to the Lightspeed modules (if any ?) we’re required. The new data plate supplied showed 170 HP.
For various reasons, mostly health related, I’ve only been able to amass 80 or so hrs since the plane first flew in 2018.
So far, I’m delighted with the engine & plane. The engine was pretty well broken in when I got it and the only problem ever encountered is it is very difficult to get the oil temperature up where it needs to be. I suspect that giant stock cooler may be needed for the 180 HP version flying at 100+ degrees, but it is way overkill for my situation (Fairbanks). I have the cooler almost entirely taped over most of the time. I plan to build a cockpit adjustable plate when I get a chance, as described elsewhere in the forum.
So far the engine has only run on 100LL, but if it becomes unavailable or even more expensive, I won’t hesitate to use 90 octane Mogas. Based on something like 2000 hrs running Mogas in my SuperCub, at various mix percentages with Avgas and for probably half that time on straight Mogas, I expect it will be fine.