984 K Road
Minden, Nebraska 68959
3O8/832-22OO
Mogas FAQ's
Q. Are fuel injected engines approved?
A. We do not have an STC for any engine with Bendix fuel injection. Continental fuel injection
is approved - I0-470 -J or -K (225hp).
The 260hp I0-470 and 285hp I0-520 are also approved but we no longer support this series of STC.
Q. Does a Petersen STC allow for the use of 82UL?
A. Yes and no, depending on the engine.
For an engine originally certificated for 87 octane or less, 82UL may be used in conjunction
with a Petersen STC. Fuel placards available from Petersen Aviation differentiate between those airplanes
that are or are not capable of using it. The original octane rating of the engine is what dictates whether
or not 82UL may be used.
82UL must not be used in engines that are approved for 91 octane mogas. The octane rating of 82UL is
too low for this type of engine.
So for example, the 150hp 0-320 which is STC'd for 87 octane (minimum) mogas may also use 82UL. However the
160hp 0-320 must not use 82UL because the higher powered version of this engine is approved for a minimum
octane rating of 91.
Q. When will 82UL become available?
A. No one knows if 82UL will ever actually be produced.
Q. I have an 0-320 H2AD, why isn't this engine approved?
A. This engine is slightly higher in compression than the other 160hp 0-320 models that were tested. Therefore
a test program only applicable to the H model would be necessary. There are not enough of them to justify the
cost of these tests.
Q. Why isn't the Mooney M-20-C (or Piper Comanche) approved?
A. The Mooney and Comanche both experienced vapor lock problems when they were tested.
We solved the vapor lock problem, but could not overcome pneumatic lock. Pneumatic lock
takes place when the fuel boils as it enters the carb. The
engine then dies due to an overrich mixture. This is just the opposite of a vapor lock
where the engine quits or runs poorly due to a lean mixture. The better an airplane
performs, the more difficult it is to get it through the flight test program.
Q. What about the Cessna 337, is this airplane approved?
A. This airframe has never been flight tested and is therefore not approved. The I0-360
engines used in the 337 have not been detonation or endurance tested and are therefore, not approved.
Q. If the Apache with 150 or 160 hp engines is approved, then why isn't the Apache with the
0-540 235 hp "B" model engines approved? These engines are listed as approved in your brochure.
A. The 235 Apache was flight tested and failed the flight test due to vapor lock. At that time
if an airframe failed the flight test it was washed out and we went on to the next airplane. There
are numerous examples of airframe/engine combinations which would appear to be approved since
they have STC's individually, but may not be approved in conjunction with each other either because they
failed the flight test or were not tested at all.
Q. Are the old Ballanca's with the Franklin engine approved.
A. No, they have never been flight tested. Any fuel pump equipped airplane must go through a flight test program to obtain STC approval.
Q. Since the 0-360 is approved, and the Cheetah and Traveler are approved, why isn't the Grumman Tiger approved?
A. The Tiger was never flight tested. The approvals from the Cheetah and Traveler cannot be extended to the Tiger
because the fuel flow on the 0-360 is a little higher than on the 150hp and 160hp 0-320's. Hence a flight test
program for the Tiger would be necessary.
Q. Since the Cardinal with the 150hp 0-320 is approved why isn't the 180hp 0-360 powered Cardinal?
A. For the same reason listed above for the Tiger. We never flight tested a Cardinal with the 0-360 engine.
Q. Do I have to change pistons in the C-152 to burn auto fuel?
A. No, not with a Petersen STC. The EAA offers an STC for 87 octane mogas which requires
a piston change. Our STC for the 0-235 L2C does not alter the engine, but it requires the use of
91 octane fuel as opposed to 87 octane.
Q. May I use fuel containing ethanol?
A. No. Go here!
Q. What about valves, will they tolerate a diet of 100% unleaded fuel?
A. It depends. There are fifty year old specifications still being used to produce valves.
These valves need a little lead once in awhile. One fillup of 100LL every 75 hours takes care of
this following engine break-in on 100LL. But once 100LL is replaced by an unleaded avgas
then you won't have this as an option. It is therefore critical, that as these
engines are overhauled, that the cylinder assemblies be replaced with parts coming straight from the manufacturer
that are specifically made to tolerate the new unleaded avgas. As far as the engine is concerned,
whether the fuel is mogas or avgas doesn't make any difference, if it's unleaded it's unleaded,
regardless of the name on the pump. Inquiries need to be made directly
to Lycoming and Continental for these parts. I am not aware of any other parts manufacturer
who build valves which will tolerate 100% unleaded fuel. It is for this reason that
these parts should be obtained directly from Lycoming and Continental.
Q. What about radial engines, will they tolerate 100% unleaded fuel?
A. Perhaps, but their TBO may be significantly reduced from what we have all become accustomed to. Our
standard recommendation for any radial is to burn a mixture of 75% unleaded mogas and 25% 100LL.
This gives a lead content equal to leaded 80/87 octane avgas, any more than this is overkill. I am not aware of a
source of hardened valves, guides and seats for radial engines.
Q. What about a fuel additive to replace lead?
A. There are no fuel additives which will protect valves and seats in the same way that
lead has. Studies done in 1988 by the EPA showed virtually all of the additives tested to be
worthless. Others have hit the market since then, but I have not seen any data which supports the
claims made by those who market these additives.
Q. Are STC's transferable from one airplane to another?
A. No.
Have another question not covered here?
3O8/832-22OO
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