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  #21  
Old 08-22-2007, 12:24 AM
Aussie 9A Aussie 9A is offline
 
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Location: Toowoomba QLD Australia
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The use of auto gas in Australia (to someone new to all of this) seems to be very limited. When I mentioned the possibility of using autogas to my instructor he commented that fuel vapour lock, and engine warrenty might be a problem. Any comments!!
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  #22  
Old 09-13-2007, 01:33 PM
hiland hiland is offline
 
Join Date: Jun 2005
Location: Tulsa, OK
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I think going with 150 HP as opposed to 160 HP in order to burn the lower price 87 octane vs. 91 octane auto fuel may be false economy. My reasoning is that at a given power setting the 160 HP O-320 will use less fuel to more than offset the higher price of higher octane. At least in my case, since 91 octane car gas is 12 to 20 cents higher than 87 octane (Tulsa, OK). I have a Tripacer that I upgraded from 150 HP pistons to 160 HP and burn easily 1/2 gallon less per hour at same power settings as before. (The engine was originally 160HP and had been derated to 150HP by a previous owner.) In addition to better take off/ climb performance, I have extended my range. Both enhancements add a degree of safety, IMHO. Plus my only fuel option when traveling is typically 100LL. I save about $2/ hour at my standard power settings burning 100LL with the higher compression pistons.

Grant Cassady
RV6 N9HJ (sold)
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  #23  
Old 09-13-2007, 02:34 PM
Stephen Lindberg Stephen Lindberg is offline
 
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Location: Olympia, WA
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  #24  
Old 09-13-2007, 02:42 PM
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N941WR N941WR is offline
 
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Location: SC
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Quote:
Originally Posted by hiland
I think going with 150 HP as opposed to 160 HP in order to burn the lower price 87 octane vs. 91 octane auto fuel may be false economy. My reasoning is that at a given power setting the 160 HP O-320 will use less fuel to more than offset the higher price of higher octane. At least in my case, since 91 octane car gas is 12 to 20 cents higher than 87 octane (Tulsa, OK).
The 80 octane 150 engine can burn regular unleaded, the lowest octane stuff you can find, as long as it is higher than 80.

There is more energy in lower octane fuel, this should be a wash, I would think. I could be wrong here, so please correct me.

This also changes the price per hour by $10/hr. (9.6 GPH & $3.75/gallon for 100LL vs. 2.71 for regular unleaded.)
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  #25  
Old 09-13-2007, 04:11 PM
hiland hiland is offline
 
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Location: Tulsa, OK
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Bill,
I'm making a case for 160 HP over 150 HP O-320. My assumption is that 160 HP engine burning 91 octane autofuel will get more miles per gallon than 150 HP burning 87 octane autofuel if both are flown at settings which produce the same power (everything else being equal). This is a result of the higher efficiency of the 8.5:1 compression ratio vs. 7:1. The 12 to 20 cents savings per gallon of 87 octane autofuel as compared to 91 octane autofuel is lost in the less efficient fuel burn.

So from a purely economic point of view for someone who knows he will never burn anything but autofuel, it would be a toss-up whether to go 150 or 160. However, the enhanced performance and range of the higher compression engine would favor the 160 HP version.

If you are saying that both engines get the same fuel efficiency when burning their corresponding octane autogas, and if you are correct, then my argument on economics to this point is wrong.

Now, there is no doubt that 160 HP (higher compression) O-320 will get a more efficient fuel burn than 150 HP will if they are both burning 100LL. My actual experience supports that. So, if one concedes that many of their fuel purchases will be 100LL out of logistical necessity, then the economic scales would also then tip toward 160 HP. The $2 per hour savings I mentioned is the difference between 150 HP on 100LL and 160HP on 100LL based on my experience with equal power output settings.
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  #26  
Old 09-13-2007, 04:51 PM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
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From what I now understand, a 160 hp O-320 can burn premium autofuel. I wasn't aware of that when I originally posted the question. I had thought that only the 150 hp variant could burn autofuel. Knowing that, I agree that there's really no reason to go 150 hp over 160 hp since the price difference b/w 87 and premium autofuel isn't very significant.

That said, if I came across a 150hp for a screaming deal, you can bet I wouldn't turn it down. As with Bill Repucci's experience, I have no doubt that 150 would power the RV-9 just fine, even for someone here in the mountain west.
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  #27  
Old 09-13-2007, 05:44 PM
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L.Adamson L.Adamson is offline
 
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Location: KSLC
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Quote:
Originally Posted by alpinelakespilot2000
That said, if I came across a 150hp for a screaming deal, you can bet I wouldn't turn it down. As with Bill Repucci's experience, I have no doubt that 150 would power the RV-9 just fine, even for someone here in the mountain west.
The 150 does just fine in the mountain west. I have approx. 40 hrs in a 9A with two people, and many flights out of KBTF (Next to KSLC), right up over the mountains to the east, and ducking below Class B airspace. You'd never feel as though you were in a Cessna or Piper at all; when it came to climb and density altitude.

Note: it has a Hartzell C/S, which is beneficial for the mountainwest too!

L.Adamson RV6A
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  #28  
Old 09-13-2007, 07:37 PM
hiland hiland is offline
 
Join Date: Jun 2005
Location: Tulsa, OK
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Quote:
Originally Posted by Aussie 9A
The use of auto gas in Australia (to someone new to all of this) seems to be very limited. When I mentioned the possibility of using autogas to my instructor he commented that fuel vapour lock, and engine warrenty might be a problem. Any comments!!
I agree with your instructor on both points. I believe Superior specifically says autofuel is allowed in their experimental engines as long as the compression ratio is 8.5:1 or lower. For certified airplanes, we can buy STC's to legally burn autofuel for airframe/ engine combinations which have been approved, eventhough Lycoming may not honor their warranty if you choose to use autofuel. Of course, once the warranty period is over, that's a moot point. You do have to be cautious and diligent with autofuel. Since we are building airframes/ engines which have not been subjected to the rigorous testing that is required for the aforementioned STC's, then we are indeed experimenting. Vapor lock is a concern even on certified aircraft with autofuel STC's. I owned a Cherokee 140 with an autofuel STC some years ago and experienced vapor lock. Fortunately, it was only temporary and I was able to descend and land under power. I believe that I made the mistake of taking off on an unusually hot day in April. The gas was probably "winter blend" still.
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