J

jscottpilot

Active Member
I am at the engine acquisition phase of an RV8 build and want to put an O-360 that will burn gasoline with an octane rating less than 100LL. I know the O-360-B1A and B1B fit this description and have a compression rating of 7.2:1 however, finding one of these engines used might be difficult. My question is, if I find an O-360 with the normal compression ratio of 8.5:1 can I rebuild it with the lower compression rating cylinders and pistons?
 
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You can burn Auto gas with 8.5:1 compressions without issue...that's the recommended limit. I have 8.5:1 and plan on burning Mogas when I can...
 
Frankh has some info about this, he should be chiming in anytime now. Apparently he runs mogas all the time in an 8.5:1 FI engine.
 
7:1 compression ratio, in an O-360, is had by installing 75413 or equivalent pistons and it is generally accepted to burn mogas with 87 octane and above with that compression ratio. Take off Hp is in the range of 168 with those pistons.

8.5:1 is the standard compression ratio for the O-360 and it is attained by use of 75089 or equivalent pistons. It is generally accepted to run mogas of 91 octane and above with this compression ratio. Rated power is 180 HP with those pistons

9:1 compression is attained by use of the LW-15357 or equivalent, in the O-360, and it is generally accepted that you should use 100LL r above with this engine. Normally see around 185 HP at take off, with those pistons.

Good Luck,
Mahlon

?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
mahlon_r said:
7:1 compression ratio, in an O-360, is had by installing 75413 or equivalent pistons and it is generally accepted to burn mogas with 87 octane and above with that compression ratio. Take off Hp is in the range of 168 with those pistons.

8.5:1 is the standard compression ratio for the O-360 and it is attained by use of 75089 or equivalent pistons. It is generally accepted to run mogas of 91 octane and above with this compression ratio. Rated power is 180 HP with those pistons

9:1 compression is attained by use of the LW-15357 or equivalent, in the O-360, and it is generally accepted that you should use 100LL r above with this engine. Normally see around 185 HP at take off, with those pistons.
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Excellent info, Mahlon. I have made a copy of your post a sticky in the Traditional Aircraft Engines forum.

Could you give us the same rundown on the O-320 piston combinations?

Thanks in advance.
 
just what I need to know

Just what I needed to know. It seems a 12 hp loss in power is alot to pay just to run regular pump gas. I guess I must decide based on the tradeoffs of power and cost but I definately do not want to be dependent on 100LL.
 
Sam Buchanan said:
Excellent info, Mahlon. I have made a copy of your post a sticky in the Traditional Aircraft Engines forum.

Could you give us the same rundown on the O-320 piston combinations?

Thanks in advance.
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The 320 and the 360 have the same bore, only the stroke is longer on the 360 to get the extra displacement. So you use the same pistons to get the same compression ratios as with the 360

7:1 compression ratio, in an O-320, is had by installing 75413 or equivalent pistons and it is generally accepted to burn mogas with 87 octane and above with that compression ratio. Take off Hp is in the range of 150 with those pistons.

8.5:1 is the high compression ratio for the O-320 and it is attained by use of 75089 or equivalent pistons. It is generally accepted to run mogas of 91 octane and above with this compression ratio. Rated power is 160 HP with those pistons

9:1 compression is attained by use of the LW-15357 or equivalent, in the O-320, and it is generally accepted that you should use 100LL above with this engine. You should see around 164 HP at take off, with those pistons.

Good Luck,
Mahlon

?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
Mahlon,

Isn't there a warning about using auto gas with electronic ignition?

Tom
RV-7A N175TJ Flying
 
tacaruth said:
Mahlon,

Isn't there a warning about using auto gas with electronic ignition?

Tom
RV-7A N175TJ Flying
Click to expand...
Tom,

This EAA document states:
EAA said:
"... it is important for a mechanic to determine whether this modification is appropriate in consideration of already installed modifications such as aftermarket turbochargers, electronic ignition systems, or higher compression pistons installed in the case of Lycoming 0-320 engines converted to 160-hp models.
Click to expand...

It does not go so far as to say EI is a no go, only that the engines tested for auto fuel did not include those ancillary systems.

Mahlon will give the definitive answer but I suspect there will not be an issue.
 
From Mahlon on the Mattituck website

"Can the TMX Series of engines be operated on automotive fuel?

Yes, all of the TMX experimental series of engines, that use compression ratios below and including 8.5:1, can be operated on fresh automotive fuel that meets spec ASTM D-4814 and has a minimum 91 octane rating. The use of automotive fuel that is blended with ethanol or alcohol is not permitted.
Engines that have been modified to use higher than standard compression ratio pistons or that are using electronic ignition that advances the ignition timing past standard specifications are not recommended to use mogas. Although the use of 91 octane automotive fuel will work in these engines, that practice should be limited and isn't endorsed."

Tom
RV-7A N175TJ Flying
 
I just found an O-360-A1G6D that came off of a duchess. Will that engine fit into an RV8. If not, what would it take to make it work? Also, does anyone know of some used engine suppliers that you trust.
 
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I know of no official tests of MOGAS with Electronic ignition. It has been reported to me that many use MOGAS and electronic ignition successfully but the possibility of problems because the timing is advancing is real. Many have used it and often promote it, but I don't feel comfortable saying it is OK for fear of trashing someone's engine due to unforeseen circumstances coupled with electronic ignition. We never tested anything like that and that is why we don't endorse or recommend it with our engines.
Good Luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
O-360 variant designations suitable for an RV8

Also, does anyone have a list of the o-360 variant designations that are suitable for an rv8 with a constant speed prop?
 
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