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  #1  
Old 04-25-2015, 06:01 PM
togaflyer togaflyer is offline
 
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Default IO 540...8.5 or 9

So I was at Sun N Fun planning my RV's future. Was talking to some engine guys about 8.5 or a 9 to 1 compression. Not really caring about adding more HP or burning mo gas. Just want a good solid engine. I was just planning to go with an 8.5, but I was told that the IO 540 actually prefers a 9-1 ratio. I know it adds some HP, but according to the engine guy, he said its better all around for the 540 series engine. Is there a difference beyond some more ponies.
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  #2  
Old 04-25-2015, 06:06 PM
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vlittle vlittle is offline
 
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Quote:
Originally Posted by togaflyer View Post
So I was at Sun N Fun planning my RV's future. Was talking to some engine guys about 8.5 or a 9 to 1 compression. Not really caring about adding more HP or burning mo gas. Just want a good solid engine. I was just planning to go with an 8.5, but I was told that the IO 540 actually prefers a 9-1 ratio. I know it adds some HP, but according to the engine guy, he said its better all around for the 540 series engine. Is there a difference beyond some more ponies.
Better thermodynamic efficiency.... AKA gas mileage. Either way, fuel injection and an electronic ignition will allow LOP operation for more efficiency.
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  #3  
Old 04-25-2015, 06:40 PM
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N941WR N941WR is offline
 
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See Mahlon's comments on this thread regarding compression ratios.

Remember, 100LL doesn't know which engine it is burning in.
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  #4  
Old 04-27-2015, 05:58 PM
togaflyer togaflyer is offline
 
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Anyone running the IO 540 with 9:1 ratio, any issue with it. Are you running electric mags.
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  #5  
Old 04-28-2015, 11:17 PM
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RV10inOz RV10inOz is offline
 
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My suggestion if you want 9:1 is to stick with standard magneto's.
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  #6  
Old 04-29-2015, 06:55 AM
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Gaylon Gaylon is offline
 
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Default 9:1

I am running 9:1 cylinders with EFII dual ignition system on 100LL. All working very well together.
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Last edited by Gaylon : 04-30-2015 at 08:05 AM.
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  #7  
Old 04-29-2015, 07:05 AM
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vlittle vlittle is offline
 
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Quote:
Originally Posted by RV10inOz View Post
My suggestion if you want 9:1 is to stick with standard magneto's.
... Somewhere in this short recommendation is a deep understanding of Lycoming engine operation. Can you educate us?
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  #8  
Old 04-29-2015, 07:21 AM
JDanno JDanno is offline
 
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Quote:
Originally Posted by Gaylon View Post
I am running 9:1 cylinders with EFII dual ignition system. Both working very well together.
So am I. Works great!
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  #9  
Old 04-29-2015, 01:36 PM
unitink72 unitink72 is offline
 
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Quote:
Originally Posted by Gaylon View Post
I am running 9:1 cylinders with EFII dual ignition system. Both working very well together.
You guys running 9:1, are you running MOGAS as well? Or sticking with 100LL?
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  #10  
Old 04-29-2015, 09:33 PM
togaflyer togaflyer is offline
 
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I checked on the Peterson aviation WEB site. They offer MoGas STCs for many engine. They have STCs for O 540's, but reading their facts and questions, they do not offer MoGas STCs for the I/O 540 version. They said it did not meet their testing requirements. Since they spent money and time to test and obtain approval for the STCs, its a good indicator that if you want Mogas, maybe you need to run a version of the O-540 engine. Just a messenger, be gentle.
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