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Old 02-16-2021, 06:11 PM
Mike Houston Mike Houston is offline
Join Date: Dec 2020
Location: Bushmills
Posts: 22
Default YIO-390-EXP119 mogas

I am wanting to build an RV 14A that runs on mogas. Does anyone know if you can convert this engine YIO-390-EXP119 to run mogas safely?
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Old 02-16-2021, 08:15 PM
Kyle Boatright Kyle Boatright is online now
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,372

Lycoming has a tech support line that might offer some help. They have always been willing to go the extra mile when I've called. Here's a link for contact info:

My immediate guess is that with the large cylinder volumes and high compression ratio, this isn't an engine that will handle auto fuel easily. I think you'll need to reduce the compression ratio for the engine to be happy on mogas over the long term.

The next question is whether they have lower compression pistons for the 390, given that it isn't a high volume item.

If you do touch base with Lycoming, it would be appreciated if you could follow-up in this thread with your findings.
Kyle Boatright
Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
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