Octane concerns...
 

I just bought a Cigarette with Merc 900SC's which run about 10lbs of boost under WOT. Here in CA we can only get 91 octane. Is it safe to run the 900SC with 91? I know Merc says 92 minimum. What can I do short of reducing my boost pressure?

Are there any additives that work well? What about mixing 108 or AV gas and at what ratio?

Thanks for the input!

The 108 octane gas I think gives a precise measurement of octane, versus boosters, and its a guess at best. I do the same thing with my procharger motor, mix Cam 2 racing fuel with premium. 108-91=17 x 10 gallons=170 wxtra octane points divided by total of 60 gallons of fuel would give you additional 3 octane points. Good luck

Those motors have knock sensors that retard ignition? If not, you could cut down your initial ignition advance a bit.

I would say if you are that close a good octane booster should do the trick. I know jdnca1 has had good luck using pump gas with octane boost, but I don't remember the name of it. When using this stuff the exhaust fumes smell just like av gas or racing fuel.

KWB;
I run 10.5:1 on 93 octane with no problems to date. When I occ spray a 175hp of NOS I typically run some octane boost just to be on the safe side. I would suggest putting in a set of very cold plugs, running some brief full throttle passes then reading ALL plugs. Look at them through a viewer to see if there is any aluminum showing up..if not repeat with a longer pass. If your plugs still check out you should be OK. If you are having problems and don't want to lower boost you either have to mix or run booster. I am not at home right now, but I will Post the booster I use. FYI, 100LL aviation fuel is basically 108 octane. I am a recreational pilot and spend some time around this stuff. I know people running merc 1000SC's on 100LL Aviation fuel mixed with premium unleaded with no problems. Aviation fuel is much cheaper than race gas here in the midwest. Let us know if the 91 works out.

SYNERGYN 120+ is the octane booster I use

Thanks for all the replies. So far the 91 has been OK, I'm installing knock sensors - hopefully they will tell me before it's too late. If I know I will be running the boat extra hard (like a poker run), I'll get some raceing fuel and mix it with the 91 at 10:1.

Ken

if you are goign to be runngin superhard fora poker run ou might as well call a racing fuel distributor and see if you can get a few 50 gallon drums to fill your boat up with. You can afford SC900 so the extra cost of CAM2 obviously isn't a problem. :D

Hell running CAM2 you could probably even crank your boostup a little more :D

Mixing 10 gallons of 108 with 50 gallons of 91 you would yield

((10gal x 108) + (50gal x 91)) / 60 gal total = 93.8 oct

To get 92 octane you need

((4gal x 108) + ( 56gal x 91)) / 60 gal total = 92.1 oct


See and we all told our 4th grade teacher this math would never be useful when we grew up.

If I have 3 apples @ 10 cents and 2 @ 15 cents how much .....

I know you are going to Havasu with Nort with the new boat, and you can buy 100 ll av gas from the 76 station out there. In the heat at Havasu I would run straight av gas for protection from detonation. I am running a blown 510 with 10# boost and have run in 120 plus degree heat at Havasu and have not had a problem with running straight av gas. I would just recommend that you buy from the 76 because I have heard of quality problems at the Supefuels there.

In California you might be able to find an airport to sell to you. In Oceanside you can access their pumps at night at the airport and just slide the credit card through and fill up. Good luck with the new boat, I was told it is vary nice.:cool:

havasucat - I live in San Clemente, so Oceanside is close. Where is the airport? Is it on the base?

Thanks

Not gunna make anyone happy...
 

I hate to rain on your parade guys, but it just doesnt work like that!

1) The different chemicals/hc's in a gas mixture yield a certain octane working together, its not always linear. In fact its not usually linear. It all depends on what the fuel 'design' was like. You could add equal amounts of 110+90 and end up with 96 or 106 octane just as easily as 100. I believe this is very much the case when TEL[lead] is involved.

2) 'Octane boosters' probably don't do much unless you are adding huge amounts of them. Most of the 'octane boosters' are just really expensive bottles of xylene, toluene, etc...

3) You have to be really sure that the two different gasolines have mixed well, or you might end up with getting a 'slug' of 91 octane fuel into the motor at the wrong moment!

4) Knock sensors will only really work on the exact enginge the sensor/processor has been designed for. Every motor 'sounds' different. Luckily most modifications will just cause 'false knock' and leave you with retarded timing, missing knock would be much more costly. I suppose you could pay someone to determine what your motor 'sounds' like when it knocks, for enough money...


Sorry guys :(

--Adam

yes i too have heard that you can't justy mix 2 different grade fuels and expect to get an octane in the middle somewhere. As for octane boosters you need alot of those little bottles. and i have hear dthey are good to keep aroudn in case you NEED gas and can't find any of teh good stuff. In yoru case if they recommend 92 and all you can getis 91 throw in a few bottles of booster (for piece of mind) and you should be fine though.

If you are interested in gasoline/octane info...

The Gasoline FAQ

--Adam

Mother
Thank for the address on the gas faq.

I knew a lot of that information from reading sometime before but helped refresh memory. Now off to get some mothballs.

KWB,

If you take the 5 south and exit on the 76 east the airport will be on your left about 1-2 miles from the 5. I went there to get gas once when they were open and it was a hassle because they made me put it in cans first. The guy who ran the place told me to come back at night (I believe after 7:00 pm) when they were closed to get gas. They run a flight school out of there so he did not want the students and instructors to see him filling up a boat, even though it is legal because boats are not subject to road tax as cars are. There is a gate that appears to have a keypad operated lock on it but it does not work. He told me just to push the gate open and pull in and fill up with a credit card. The pumps are right next to the gate. I hope this works for you.:cool:

Mixing different types, and octane fuels will not give you a happy medium. Although it will help your octane total, there is no way to say how much without having it tested, it may not even mix at all. Because of the different chemicals in fuels the won't always mix together.

I had heard before that 100LL avgas was not much more octane than 92 unleaded. I think the deal had something to do with the avgas being rated in a manner that shows a higher reflective number than what we have on our auto gas pumps - something like the Research Octane and Pump Octane being rated differently.

Also, a friend with a Beech Bonanza with a flat-6 motor now can use 89 octane unleaded in it. The motor supplier said that the only difference in the motor in its "110LL" configuration and the "89 unleaded" configuration is the material of the exhaust valves, the valve guides, and the exhaust valve seats. The ignition map and the power output are unchanged, as is the compression ratio, etc..

This leads me to be suspicious of the avgas octane system in relation to car gas and race gas ratings.

Any thoughts??

Tell your friend to be careful. He will need to watch his altitude and listen for engine changes. The vapor point of avgas is much higher than auto gas. What this simply means is that as altitude increases, the ability of the gas to not vapor lock in the fuel lines is affected. If the aircraft engine is fuel injected and the pump is in the tank, than all should be well. I hope this helps.

I agree AV-gas is alot different than 91 street fuel the Union 76 rep told me it is made to burn better at altitude where not much oxygen is avaiable to burn and it says LL but it has twice the lead of the old street fuels ( sunoco 260 ) ect.
But his thought were it should do good in the marine enviroment and is rated at 100 MIN. but could be as high as 108 ??

I know alot of people who run the stuff all the time and it works great for them

If they will not mix, will they have one have a tendency to lie on top of the other? Like water on oil.