IO360 and mogas

Bruinpilot · #1 07-10-2014, 02:03 PM

I have read several posts where people are debating the merits of mogas vs 100LL. I can't seem to find any good thread on the modifications required to tolerate the ethanol in mogas. I am considering building an rv7 someday with the IO360, possibly electronic ignition. Just want more info on the possibility of using Mogas. Thanks

LettersFromFlyoverCountry · #2 07-10-2014, 02:32 PM

Go here. And download the December 2013 newsletter. Pete Howell has a good writeup.

You can never go wrong listening to anything Pete has to say.

petehowell · #3 07-10-2014, 02:53 PM

My wife has other thoughts on the value of any information from this guy named Pete Howell.

Mogas use is a complex topic with many opinions on both sides. It has worked well for me in an O-320 with Electronic Ignition. YMMV.

Fuel Quality, compression ratio, ignition timing, and other factors are important considerations.

A good place to start are the archives here(search button) and at Avweb.

Given the price and future of 100LL - it is good to have options.

Bruinpilot · #4 07-10-2014, 02:54 PM

Thanks, that newsletter is great. I still wonder if there are any mods possible to make the fuel system ethanol friendly. I really like the idea of running one tank 100LL for take off and landing and keeping another full of mogas.

BillL · #5 07-10-2014, 02:55 PM

Talking about 100LL in the $6 range and premium gasoline without ethanol at $4XX then the $2 gal savings at 7 gph is worth considering to me.

No ethanol for me though, not in an airplane - vapor pressure reasons.

krw5927 · #6 07-10-2014, 03:12 PM

Quote:

Originally Posted by BillL

No ethanol for me though, not in an airplane - vapor pressure reasons.

My take as well. Having designed and built a completely ethanol-tolerant fuel system, I found very early in Phase 1 testing that the higher Reid Vapor Pressure of mogas will likely prevent me from using any mogas in my airplane.

brown bear · #7 07-10-2014, 03:42 PM

IO360 and mogas
http://fuelschool.blogspot.com/2009/...l-blended.html
Read this and then do you still want ethanol ?
Doug

KJBSouth · #8 07-10-2014, 04:04 PM

The second paragraph of Howells article defines Mogas as fuel with no ethanol. I have an STC for the Swift and have been running Mogas for several years with no problems. Test each batch for ethanol an haven't found any yet. I would never use automobile fuel (ethanol) for vapor pressure reasons. It is recommended to run a tankful of 100LL occasional to keep a little lead on the valve seats.

Using Mogas in the -7 with an IO360 is in our plans.

fly safely.

krw5927 · #9 07-10-2014, 04:30 PM

My vapor pressure problems were with ethanol-free mogas. Look at the ASTM specs for mogas. The Reid Vapor Pressures specified are, most times of the year in most locations, significantly lower than that specified for 100LL. Many people run mogas with no problems. I couldn't.

RV10inOz · #10 07-10-2014, 04:49 PM

Gooday folks, I am not sure how many of you have actually done any real live testing of various fuels on an aero piston engine dyno, and certification testing for the FAA at that, but here are my thoughts on mogas in an IO320/360/540.

1. RVP is a problem and while one VAF member has built a system to mitigate against it I believe he still runs Avgas in one tank.

2. Latency, so with mogas and EI you get a peak pressure much higher and much closer to TDC than you do with the engines designed fuel and magneto's. Part of the reason those who do have extreme lengths to keep CHT's under control. They then get slightly better control of CHT but the ICP remains.

3. Gum buildup from much higher olefin content. Not worthy of the risk in my opinion. I have enough troll with my large HP outboards running good mogas.

4. No controls in place.

5. Finding, carting and storing (laws and by-laws, insurance) and the overall pain in the butt doing so.

6. Avgas is not going to vanish, it will become lead free, but it will remain.

You can run it in your carb engine as the RVP problem is less of a problem?..but the other factors remain.

These are not my opinions. These statements are from real data.

Pick your poison carefully, but do not buy one thing on the basis avgas will vanish, as 75-80% of the consumption is by folk who will not let that happen, and private O320 flyers are not in that bunch. The 80/20 rule applies here.

Hope that helps.