8.70:1 Compression/Mogas?

D.A.

FRIEND

Free America

• May 31, 2014

• #1

We're considering running a 200HP Angle Valve engine modified with an O-360 Sump and carb to fit it in the SC cowl but we want to be able to run Mogas. I did some searching on the forum and I can see where the carbureted 8.50:1 Lycomings are running Mogas without issue, but I didn't see any specifics about running Mogas in higher compression engines. I know there are guys out there with 10:1 and maybe even higher, and I know guys run Mogas with high compression pistons, but I don't know where the break over point is. We'd like to keep the stock 8.70:1 200HP pistons, with the Mogas that is typically available out there, do those of you that have “Been there - doing that”, do you feel Mogas can be run in a 8.70:1 carbureted engine?

Thanks in advance for the input.

 

Last edited: May 31, 2014

DW

Registered User

pacific northwest

• Jun 1, 2014

• #2

It will need to be 92 octane or better and you should have no problem or you can run a blend.

 

J

JimC

Registered User

• Jun 1, 2014

• #3

I've run 9.5:1 on 93 octane mogas.

 

D.A.

FRIEND

Free America

• Jun 1, 2014

• #4

DW said:

It will need to be 92 octane or better...you can run a blend.

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Perfect, I was hoping you were going to chime in. We’re mimicking your set up in a lot of ways; Big engine for everyday use, big engine with Nitrous for when you really need to get out of the hole! I ordered the 78915 O-360 Sump the other day and I’m shopping for an MA4-5.
I’m glad to hear 92 Octane should do the trick. I know you guys are probably well familiar with this site, http://pure-gas.org Our own Bugs66 is a regular contributor as far as Ethanol Free locations in his region when he finds them.There are several places offering 92 Octane but 91 Octane is all over. 85% 91 Octane Mogas plus 15% 100LL works out to be about 92.35 Octane and I like the idea of getting lead back in the fuel.

JimC said:

I've run 9.5:1 on 93 octane mogas.

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That’s good to know Jim. If your 9.5:1 survived 93 Octane, our 8.7:1 on 92+ should have no problem.
Thank you guys for the feedback.

 

D

don d

Registered User

don

• Jun 1, 2014

• #5

Don't run more than 27". Not a problem over 4000 ft. Expensive engine to screw up.

 

cubdriver2

FRIEND

upstate NY

• Jun 1, 2014

• #6

I've run 8.68 on 89 efree with out any detonation in C85 stroker with C85 pistons but don't push the timing too far.

Glenn

 

Cub Builder

MEMBER

North Central AR

• Jun 2, 2014

• #7

I run an O-320 and an O-200, both with 8.5:1 compression on E-0 90 aki mogas. The O-200 also has electronic ignition with advance up to 39 degrees at altitude. I've not noted any issues, but am also based above 7000' MSL.

-CubBuilder
My planes web site

 

D.A.

FRIEND

Free America

• Jun 2, 2014

• #8

don d said:

Don't run more than 27”...

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With most of the airplanes I’ve flown, with the restrictions of the air filter, the induction system and so on, I’ve never been able to get more than about 27”MP at sea level anyway. I’m guessing the Cub will be about the same. Some of the IAC guys will run their Pitts without air filters with a forward facing inlet sump to get a little ram air effect. I’m told they can get closer to 28”.

Cub Builder said:

I run an O-320 and an O-200,both with 8.5:1 compression on E-0 90... but am also based above 7000' MSL.

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7000’ - - - Holy Cow! Does that give you some where around 21” or 22” max? I bet 90 octane would work just fine in those conditions. Seems like high compression pistons in an airplane based at that altitude would be a natural mod, if you can’t cram more in, then squeeze what you’ve got harder!
Good input – Thanks to all.

 

180Marty

MEMBER

Paullina, Ia

• Jun 2, 2014

• #9

then squeeze what you’ve got harder!

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That's what makes ethanol such a good fuel. That and it burns so clean. Ethanol is the cheapest "octane" on the planet at this time.

 

Cub Builder

MEMBER

North Central AR

• Jun 2, 2014

• #10

D.A. said:

7000’ - - - Holy Cow! Does that give you some where around 21” or 22” max? I bet 90 octane would work just fine in those conditions. Seems like high compression pistons in an airplane based at that altitude would be a natural mod, if you can’t cram more in, then squeeze what you’ve got harder!

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Yeah. I'm pretty much limited to about 22.5" MP here. Could probably run Coleman lantern fuel at this altitude without detonation. :lol: But I do get to lower altitudes occasionally as well and see no difference in performance or temps between 100LL and 90 aki Mogas. Lycoming says minimum or 91 aki minimum for 8.5:1 for sea level ops and they have a pretty big margin for things to go wrong.

180Marty said:

That's what makes ethanol such a good fuel. That and it burns so clean. Ethanol is the cheapest "octane" on the planet at this time.

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Other than dissolving my glass tanks, it would work fine. :sad:

-CubBuilder