Auto fuel....again

[Ursa Major]

I was recently thinking about how I should rebuild my engine (O320-B2B -160 hp) when it becomes necessary. It has around 1200 hours SMOH and seems to run just fine (just keeping the fingers crossed that it will for a bit longer).

Anyway, when I filled up today ($3.28 for 100 LL with a discount) I began to think seriously about converting the 160 to a 150 at the next rebuild in order to use auto fuel under STC. I know that Pederson's has an STC for the 160 that uses 91 octane auto fuel- but I just can't find 91 octane at any of the local stations. The solution would seem to be a rebuild back to 150 hp (or rather low compression) and maybe trying to increase hp by exhaust mods or other means to get the extra 10 hp back while still being able to use 87 octane.

I know I could probably operate on the 90 octane currently available without any serious problems- I just want to stay legal (or at least compliant with the STC) for insurance reasons.

Anybody have comments on converting my B2B back to 150hp, or is it a really stupid idea?

BTW I don't operate on floats so the 10 hp difference is probably not that big a deal.

[Redbaron180]

A friend of mine recently purchased a 160 hp cub that has stock exhaust and prop. I have a 150 hp cub with with LE exhaust and borer prop. He out climbs me by no small amount. It seems like LE claims 16 hp increase with their exhaust, I don't think so, unless my buddys engine has something else that we don't know about. I'm not disappointed with the LE system though, it has definite advantages over the stock system.
I think you will find the 160 hp will burn less fuel per hour and might about make up for the difference in cost. If I could have my buddy's power I don't think I'd change, though mine is smother.

Ron

[SJ]

RB180,

In my limited experience, the 10hp from the 150 to 160 can make a substantial difference, as can different props and of course weights.

sj

[JP]

The resident sages at my current roost really think the world of the 160 hp engine over the 150. Kind of like the C-90 v. the C-85. There is a big difference according to them.

[jnorris]

I know that Pederson's has an STC for the 160 that uses 91 octane auto fuel- but I just can't find 91 octane at any of the local stations.

Where are you located? What is the anti-knock rating of the premium auto fuel in your area? Usually premium auto fuel is at least 91 AKI (anti-knock index). Remember that the STCs call out a minimum AKI, but you can run a higher AKI fuel with no problems, so if you can find 92 or 93 AKI premium auto fuel the Petersen STC would work great on your 160 hp Lycoming. (Remember that the number shown on the pump, and called out in the STCs, is an anti-knock index derived from averaging two different methods of determining octane.)

That being said, if it were me I'd prefer the 150 hp version, just because I could run the regular auto fuel (87 AKI minimum) with no problems. I'd be totally happy with 150 hp. (But then again, my Super Cub is a 90 hp Continental, so a 150 hp bird would be a screamer compared to what I'm used to!! <grin>)

Joe

[Ursa Major]

Joe,

Here in Anchorage the highest octane rating I've seen (on the pumps) is 90. If I could get 92 or even 91, I'd just get the Petersen STC and press on. Problem is, even the minimum STC level of 91 is not readily available.

So is the AKI rating different than what is shown on the pump? Is it possible that the 90 octane shown on the pump is within the specs for the STC?

[jnorris]

So is the AKI rating different than what is shown on the pump? Is it possible that the 90 octane shown on the pump is within the specs for the STC?

The numbers on the pump, and required by the auto fuel STCs, are anti-knock index (AKI) numbers. These are not octane ratings, but rather are an average of two different methods of measuring octane. Auto fuel with an AKI of 87 is roughly the same octane as 80 octane aviation fuel (actually just slightly higher), which is why the majority of auto fuel STCs require auto fuel with an AKI of at least 87.

Your 90 AKI fuel will not satisfy the Petersen STC, which requires auto fuel with a minimum AKI of 91 for the higher-compression engines (like the 160 and 180 hp Lycomings). If you don't have a supply of 91 AKI fuel or greater, you won't be able to use the Petersen STC on your 160 hp engine.

Joe

[kase]

Anyway, when I filled up today ($3.28 for 100 LL with a discount)
BTW I don't operate on floats so the 10 hp difference is probably not that big a deal.

I paid $3.40 for 100LL in Miles City last weekend. I got 160 and it seems to out perform every 150 cub I have been around except the stripped non elec ones. Everybody here that converted to 160 gained 75-100 rpm using the same prop. I would have a hard time going back to 150 hp.

[wilbur]

Another thing to consider is not only the difference in the 10 hp by itself, but the difference in performance gained by using the 100 over the 91. I normally run the premium gas in my 88 inch bike, but sometimes fill with the 102 that a local station carries. The performance difference is instantly noticable, and there's a definitely sharper "pop" when it's being spanked. I ran 100 in my last J-3, and it would idle smoothly at 275 rpm, just above the impulse mags. The next owner ran tractor gas in it, (could have been 87), and he had to set the idle up at least a 150 rpm. Just my experience with gas.
Wilbur
PS- I'd be curious what the difference in static, or climb out rpm would be between the 91 and 100.

[Ursa Major]

Thanks for all the well reasoned replies. I guess I'll probably rebuild as a 160 B2B when the time comes. I suppose I will get the Petersen STC if I eventually find some 91 octane autofuel - otherwise I'll continue to bite the bullet and pay the price for 100LL.

Its been so long since I flew a stock 150 hp cub that I forgot the performance improvement with 10 more horsepower. Now if I could only find a low compression O-360 180 hp that would be compliant with the STC and get it approved....hmm.

[T.J.]

delete

[diggler]

XX

[S2D]

I paid $3.40 for 100LL in Miles City last weekend.

thats what you get for not waiting till you got here!

[Christina Young]

Radial and Franklin engines should use this mixture at all times because they are much more dependent on lead for lubrication.

You've got to be kidding. I have a Franklin in my Stinson, and if I use even a little 100LL without also using TCP, I have fouling problems almost immediately! Therefore, I use 100% 87 octane autogas in that engine, never any problems, engine runs like a sewing machine.

[bob turner]

We used 100LL in our Franklin 180 without any problems at all. World's most beautiful Stinson! Now up in Valdez.

[Mikey]

I was in ANC last weekend and noticed the pump I filled the rental car up at had a placard stating "Use in aircraft prohibited" or something to that effect. Never seen that on pumps down here in WA. Is it just a CYA thing? Don't remember the brand , but was at a station out on Tudor @ Lk Otis
Chris

[Ursa Major]

I was in ANC last weekend and noticed the pump I filled the rental car up at had a placard stating "Use in aircraft prohibited" or something to that effect. Never seen that on pumps down here in WA. Is it just a CYA thing? Don't remember the brand , but was at a station out on Tudor @ Lk Otis
Chris

Chris,

I think that placard is probably a carryover from when alcohol was used as an oxygenate during the winter to meet emissions standards. I have been told that they no longer use alcohol in Anchorage auto fuel. BTW, both gas stations at the corner of Lk. Otis and Tudor are now closed - soon to be replaced with a wider intersection.

[ag-pilot]

I put a couple thousand hours on a 160 over half of it with regular unleaded. The engine had 2300 SMOH on it and was running great when I sold the plane. Last year I talked to the new owner who was uncomfortable with the high time engine and sent it off to have it majored. He stated that the shop said the cylinders/ pistons/ cam/bearings were all still in spec. with no unusual wear. The engine then had 2400 hrs. I had always used 20/50 XC and everything was nice and clean inside he said.
Dave

[mvivion]

Alcohol content is the other wild card, besides anti knock rating in auto fuels.

In past, it was pretty clear that most of the auto fuels in Alaska didn't meet the requirements of either of the auto fuel stc's, due to presence of alcohol. And the problem with the alcohol up here was that it wasn't predictable, seasonally. Seems like they were sometimes getting batches of whatever was left over.

The best advice one can get, I believe, is to acquire a copy of the stc requirements from either EAA or Peterson, and read them very carefully. There are a lot of gotchas in there, if a person isn't careful.

Not to say your airplane will instantly enter a "tail spin" as the media says, if you use the stuff. My point is simply that you should be well informed of what you're using in a very expensive piece of equipment.

Note the requirements for testing each batch of fuel, for example.

MTV

[Mikey]

Chris,

I think that placard is probably a carryover from when alcohol was used as an oxygenate during the winter to meet emissions standards. I have been told that they no longer use alcohol in Anchorage auto fuel. BTW, both gas stations at the corner of Lk. Otis and Tudor are now closed - soon to be replaced with a wider intersection.

Must have been more toward Tudor & C. Thanks
CD

[Ursa Major]

The best advice one can get, I believe, is to acquire a copy of the stc requirements from either EAA or Peterson, and read them very carefully. There are a lot of gotchas in there, if a person isn't careful.

MTV

Good advice Mike. I'm just trying to stay legal (and safe).

[RYAN_WINGS]

could you not add octane booster to the fuel to boost your 90 octane level up to 92 or so???
It is not that expensive and can be bought in any automotive store.
I use that toboost the performance of the fuel for a small motocross bike, really makes a difference....

[Ursa Major]

could you not add octane booster to the fuel to boost your 90 octane level up to 92 or so???
....

I suppose you could, but it would not be compliant with the auto fuel STC, and might present a problem if you had an insurance claim while using it. That said, I wouldn't be surprised if 90 octane worked just fine (with maybe a little 100LL mixed in) - it just wouldn't be legal.