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: