Mogas FAQ

Q. My airframe/engine isn't on Petersen's list. Where else can I check?

A. Check with us by phone 308.832.2000 or email todd@gtmc.net or you can also click here to check EAA’s list of approved engines and airframes.

Q.Where can I find airports selling auto fuel in the United States

A. To find airports that sell mogas in the United States check out: Air.Nav.com or Mogas Planning Map

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. This series of STC’s are now being supported by Air Plains Services.

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 Continental 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 website.

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.

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, 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 parts compatible with a steady diet of 100% unleaded fuel. Smaller Continentals must have lead during break in even with cylinder assemblies obtained from 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. We are 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 we 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.