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brwn234
06-08-2009, 10:49 AM
What octane fuel do you put in your boat? I've been using 93 but I'm thinking it may just be a waste of money. It's only a stock 7.4, not some built motor. Shouldnt I be fine with regular fuel if it doesn't sit too long before I burn it up? I know that the newer ethanol looses ocatane quicker and draws moisture.

The Hedgehog
06-08-2009, 11:03 AM
What octane fuel do you put in your boat? I've been using 93 but I'm thinking it may just be a waste of money. It's only a stock 7.4, not some built motor. Shouldnt I be fine with regular fuel if it doesn't sit too long before I burn it up? I know that the newer ethanol looses ocatane quicker and draws moisture.

If your gas does not sit too long, you are fine with 87. Stock merc engines have a pretty conservative tune.

zelatore
06-08-2009, 12:30 PM
What Hedge said.

No point buying premium. It won't make a difference to a motor that doesn't need the higher octane, it'll just make a bigger hole in your wallet. Better off buying regular and a bottle of Sta-Bil for when you lay it up for any length of time.

roadtrip se
06-08-2009, 02:05 PM
Anybody want to throw an explanation out there for why I smelled so much racing fuel this year at AOTH? At times, I felt like I was at the drag strip on Saturday night, there were so many fumes in the air.

The few that I have asked basically state that the raised octane mixed in with the normal stuff, is just "good insurance" for stale fuel from winter.

What does the high, high octane really do for the "Big Dogs"? This puppy wants to know....

The Hedgehog
06-08-2009, 02:40 PM
Anybody want to throw an explanation out there for why I smelled so much racing fuel this year at AOTH? At times, I felt like I was at the drag strip on Saturday night, there were so many fumes in the air.
The few that I have asked basically state that the raised octane mixed in with the normal stuff, is just "good insurance" for stale fuel from winter.
What does the high, high octane really do for the "Big Dogs"? This puppy wants to know....

Not that I am a "Big Dog" but I was one that had race gas in my boat at AOTH. A number of us use it for exactly what you said. Insurance after the winter. I carry a mixing chart in my boat also in case I am stuck somewhere that only has 87. I can get back home without boost and blend in some 110 to get mine back to 93. My boat was tuned for 93 so I don't really try to go higher than that. If I filled up with 110 it would be a waste.

Now there are a few occasions I run my boat harder. On those, I may throw in some 110 to compensate for any potential issues (buying older gas from a station that does not turn much, unforseen tuning problems etc). I doubt that I am taking it past 94-95. The way I see it is that 94 is better than 90

I love the smell though. Even if you only use 10% race gas, you can smell it.

To bad it does not help protect blowers:lookaroun:

brwn234
06-08-2009, 03:10 PM
Thats what I figured. I'll start using 87 while I'm using the boat almost every weekend. When I start using it less I'll start mixing in high test.

rtgogo
06-08-2009, 04:16 PM
Good to know....I wasn't sure she needed it, but won't feel as compelled to insist on premium during the season now....

Barry Eller
06-08-2009, 05:50 PM
My engine has dry offshore exhaust and its not equipped with a "Knock Sensor", I will NOT hear it "ping" from premature detonation.

Usually 93 octane gas is approximately .20/.25 cents a gallon more than 87 octane in my area. My 22C holds 50+- gallons. So for around $10.00 a tank, I get some CHEAP INSURANCE against burning a hole in a piston. 89 octane is only around .10 cents a gallon more than 87 octane. 50 gallons= $5.00 difference.

There are "knock modules" available for non computerized setups like I have. Does anyone have any experience using them?

Some say that 87 octane will make you faster than 93 octane...maybe a little, but a burned piston or valve will make you slower!!!

MOP
06-08-2009, 06:53 PM
Using HT in the lower compression engines is a waste, you can actually lose some power.

The Hedgehog
06-08-2009, 06:53 PM
I don't think that many of us would hear it ping unless it was probably too late.

I have a friend that uses a knock sensor on carb engines. He is running high compression AND a blower. I went tuning with him one day. He changed jets and air bleeds about 15 times. I thought he nailed it pretty good. I talked to him a few days later and he was out to tune some more. He says it is all in the tune. So far so good for him.

With EFI engines, running too high of an octane you can screw up the air/fuel mixture since injectors are calibrated to run at lbs/hour and the fuel density will be higher or lower depending on the octane. I dunno how this effects carb engines but I have heard that too high is not necessarily good either.

If you really want insurance and you are running a carbed engine, you will tune it with an A/F meter. Just slapping on a carb to a crate engine can be more dangerous than having your octane a point or two low.