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  #21  
Old 03-16-2017, 07:40 AM
BillL BillL is offline
 
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I am sure Petehowell has posted this on VAF, but here is a link (access Dec2013) to his graph of 100LL and mogas mix. Also, note his test apparatus for Reid Vapor pressure. This should be of interest for those flying with a fuel system without tolerance to high vapor pressure fuels. Carry some test equipment and know your temp/altitude limits.

The RV drivers need to know what the limits are for the fuel/fuel system combination. It is just too risky "hoping" it is ok. Especially if locked into using mogas.
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  #22  
Old 03-16-2017, 07:42 AM
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Quote:
Originally Posted by David-aviator View Post
At that time the Hodges tester was sold by Petersen with the mogas STC kits for various engines..... In fact I believe he stopped selling the tester, maybe because of liability issues....
I understand that general reductions in the volatility of US fuels resulted in reduced demand for the testers to the point where Petersen decided to send their remaining stock back to Dr Hodges in Australia.
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  #23  
Old 03-16-2017, 07:57 AM
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I've seen some boiling point comparisons of winter mogas and some were as low as 105F at SL- lower at several thousand feet. Food for thought on a warm engine with heat soaked carb float bowls.
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  #24  
Old 03-16-2017, 08:15 AM
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Quote:
Originally Posted by Piper J3 View Post
Itís not the seasonal vapor pressure blend of the auto fuel, but rather the residual heat after engine shutdown that causes the fuel to boil off in the carburetor float bowls as I described in my post #10.
Actually it is both.

The vapor pressure of the fuel definitely has an influence and is a variable so operators need to keep it in mind in warmer temps in the spring early summer.
Particularly with specialty fuels (non ethanol) that could have a low sales volume and have been sitting in the retail tank for quite a while.
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  #25  
Old 03-16-2017, 08:20 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by DonFromTX View Post
IF using Decalin or TCP, does that mean you can change oil at non leaded intervals, and none of the bad things from lead will happen to your engine?
No, the same leaded fuel maint. intervals are recommended regardless of whether you use a lead scavenging additive or not.

BTW, use of 100LL doesn't cause any "bad things" to happen with a Rotax, but if you are looking for something to push the Viking higher on the "benefits" chart I guess this might be one. Though with so few engines in service, does anyone actually know what the long term (many hundreds of hours) effects of 100LL is on a Viking installation?
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  #26  
Old 03-16-2017, 09:00 AM
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Quote:
Originally Posted by rgmwa View Post
I understand that general reductions in the volatility of US fuels resulted in reduced demand for the testers to the point where Petersen decided to send their remaining stock back to Dr Hodges in Australia.
Robert,

Is the Hodges test kit available in Australia?
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  #27  
Old 03-16-2017, 09:05 AM
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Quote:
Originally Posted by rvbuilder2002 View Post
BTW, use of 100LL doesn't cause any "bad things" to happen with a Rotax...
Oil change intervals are reduced using 100LL and Rotax techs tell me that gearboxes on engines using 100LL are pretty gunked up with lead, even with the shorter oil drain intervals.

Lead isn't good for a Rotax but the characteristics of the 100LL fuel itself is superior in hot and high conditions from vapor lock formula consistency perspectives.
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Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW- 412.1 hrs. on the Hobbs,
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http://www.sdsefi.com/aircraft.html
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  #28  
Old 03-16-2017, 09:24 AM
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The one negative about having to go from an IO-360 to the Rotax in the RV-12 I'm building is having to go back to a carbureted engine.
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  #29  
Old 03-16-2017, 09:26 AM
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Quote:
Originally Posted by AZLeeJay View Post
Thanks for the info Bob, I think I'll add a little 100LL next time I add some gas. Do you know when they change to the summer blend here in Az?
Although I have a friend here who works at the local refinery and gives me heads up (I'm in MInn), the best way to know when they've switched to the summer blend is when your car picks up about 4-5 mpg on a tank.
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  #30  
Old 03-16-2017, 09:34 AM
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Very good conversations here. Thanks for chiming in Scott...
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