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BassFooler
07-22-2005, 09:36 AM
Just a qucik poll-
For those of you with 4 stroke outboards- what is your fuel preference regarding brand and grade?

drstressor
07-22-2005, 10:00 AM
Chevron mid-grade, 89 octane.

jackstraw
07-22-2005, 11:44 AM
Same as Doc... Chevron 89 octane, no problems so far.

Zucca
07-22-2005, 01:47 PM
Chevron midgrade. It is especially good if your motor is used for trolling since it seems to prevent fouling of the plugs better than most of the other major brands I have tried.

sunracer1957
07-22-2005, 03:15 PM
I'm a Chevron guy Too, it always seems to cost a few cents more than other brands but I'ts worth it if you ask me,, I troll with my 150hp and a Plate and I never load up using this gas..

Mickey_Thomas
07-22-2005, 04:42 PM
Doc knows I'm a Chevron guy too ;) I made him stop every 200 miles at whatever Chevron he could find ;) I was told my North River that I could use 87 in the Yahama 150 but still use the 89, I figure use what you know(and whatever Doc uses) ;D ;D

krzyfshrmn
07-22-2005, 05:59 PM
You guys are wasting money. I watched a show the other night, (20/20 or 48 Hours investigates) and gasoline was the topic. After several interviews with oil company reps, to Nascar drivers, it's become a proven fact that higher octane fuel in no way, burns cleaner, improves gas mileage, or makes engines perform better, with the exception of high performance engines such as Ferrari, Marcedes, or profesional race cars. 87 octane is just fine for anything else.

And while all oil companys claim to have the best gas, it does'nt matter if you pump it from Chevron, 76, Mobile, or Joe's Quicky Mart. You're getting the same product, that was made in the same refinery.

Save your money for important things, like fishing gear. Fill up at the cheap place for both boat, and tow vehicle. ;)

Off_The_Hook
07-22-2005, 09:50 PM
Even though most newer engines are rated for 87 octane, I won't put anything but Chevron 91 in mine. Chevron has Techron additive, which is actually reccomended by Yamaha, and is a very effective fuel system cleaner. The higher the octane rating, the slower the fuel mixture burns, which can result in a cleaner, cooler and more efficient burn. It also will detonate less, which means the engine computer does not have to retard the timing as much, resulting in more power. Fuel also looses a point or two of octane rating after it sits for a while. Now I realize the advantages of premium vs regular may be minor in reality, or may only exist in my imagination, but when you got $13,000 in engine hanging off the back of your boat, an extra 10 cents per gallon is worth it to me. Just my 2 cents worth.

drstressor
07-24-2005, 10:09 PM
Krzy, you need to stop watching so much television. ;D

While I agree that the octane rating of fuel has nothing to do with how clean it burns except in high compression engines, premium fuels typically contain more of whatever additive package is used by the particular brand. It's the detergents/dispersants in the add pack that reduces fuel system and cylinder deposits, not the octane rating. However, a little higher octane is a good thing for boat fuel because it tends to sit around longer before it is burned than automotive fuel. The octane rating of fuel drops with storage. So an 89 or 91 octane fuel takes longer to drop below the critical 85 octane level than fuel that starts out at 87 octane.

SuperDave
07-25-2005, 06:30 AM
Not only do I typically us the mid to high octane fuel, I usually throw in a $5 bottle of octane boost. If I am boating here in the valley, I'll use the mid grade. High elevation = high grade + boost.

drstressor
07-25-2005, 07:43 AM
You have it backward Hinrid. The octane requirement for a normally aspirated (non-turbocharged) engine decreases with altitude. That's why regular gas sold in the mountains states is only 85 octane. An engine draws in less oxygen with each intake stroke at high altitude, so faster burning fuel actually works better.

Octane rating is a measure of the resistance of the fuel to pre-ignition. High octane fuel burns slower but actually releases less energy per unit volume than regular fuel. As Krzy pointed out, you need a higher compression engine (or a supercharger)in order to realize the power potential of higher octane fuels. You can actually reduce the performance of a lower compression engine if you raise the octane level of the fuel too high. Again, the only advantage of using higher octane fuel is to realize the advantages of the other additives and to minimize the decline in octane that occurs during prolonged storage.

The only reason I even bother with mid-grade Chevron is because I only fuel up the boat 2-3 times per year. For my car and truck, I buy the cheapest fuel available and run a bottle of Techron concentrate through about every 3-4 K miles. If I was fueling my boat up every few weeks, I would run 87 octane fuel. The upper cylinder deposits that cause engine manufacturers to recommend mid-grade fuel are the result of fuel getting stale

SturgeonVirgin
07-25-2005, 08:07 AM
Krzy, you need to stop watching so much television. ;D

While I agree that the octane rating of fuel has nothing to do with how clean it burns except in high compression engines, premium fuels typically contain more of whatever additive package is used by the particular brand. It's the detergents/dispersants in the add pack that reduces fuel system and cylinder deposits, not the octane rating. *However, a little higher octane is a good thing for boat fuel because it tends to sit around longer before it is burned than automotive fuel. The octane rating of fuel drops with storage. So an 89 or 91 octane fuel takes longer to drop below the critical 85 octane level than fuel that starts out at 87 octane.


Doc is right; Chevron, Shell and Texaco are some of my customers, and I have talked to them about this for years. The only difference is the additives which are by the way extremely expensive. The best one out there is Chevron, then Shell, then the rest, it seems the first two are the ones spending more on R&D for these issues than anyone else; I go onsite to the refineries, and the majority of them are only producing gas, not developing better additives.

drstressor
07-25-2005, 08:18 AM
You have pointed out the top tier fuels Mr. T. Texaco and Chevron use the same additive package these days since Chevron acquired Texaco. Even their motor oils (Chevron Supreme and Havaline) now look to be the same formulations from recent oil analysis data.

Chevron, Shell, and Exon Mobil spend the most on fuel and lubricant R&D.

SuperDave
07-25-2005, 08:54 AM
You have it backward Hinrid. The octane requirement for a normally aspirated (non-turbocharged) engine decreases with altitude. That's why regular gas sold in the mountains states is only 85 octane. An engine draws in less oxygen with each intake stroke at high altitude, so faster burning fuel actually works better.


So I've drawn the wrong conclusions? I had noticed that the highest octane boosts were rated for "off road", assuming more power. How about boats that idle worse at high altitude, higher octane doesn't help them run smoother?

drstressor
07-25-2005, 10:39 AM
Higher octane doesn't help. What helps is leaning out the fuel mixture. Engines with oxygen sensors do this pretty well. Most carbureted engines need different jets. The right air to fuel ratio smooths out the idle and prevents the plugs from fouling from running too rich.

drstressor
07-25-2005, 11:09 AM
Here is link that explains a bit about "Top Tier" gasolines. This is new industry standard.

http://toptiergas.com/index.html

dirtydan
07-25-2005, 11:14 AM
Don't want to get off topic - but the high altitude question . . . my boat was brought here from Utah - it is (was?) set up for high altitude operation (different outdrive gears). What happens to an engine set up for high altitude operation comes back down to earth? Would it tend to run too lean? Should I swap out the jest (if it hasn't been done already)?

Also - I've heard it's not good to use cleaning additives - particularly on older boats (15 yrs +) because of the effect the additives have on the fuel lines - any truth to that?

-DD

SuperDave
07-25-2005, 11:24 AM
DD, where do you use your boat the most? My last boat was an old carburated I/O and I had it jetted for where I used it the most. When I went somewhere different in elevation, I always lifted the engine lid and put a couple twists on the air/fuel mixture screw until it sounded like it was running at best rpm's. Making many trips from valley to foothills and back required lots of fine screw adjustments. Thanks to EFI, no more screw driver.

drstressor
07-25-2005, 11:49 AM
DD, the final drive ratio shouldn't present any problems. If you find that you are over-reving at sea level, just get a bigger prop. If the engine, particularly an older engine, was jetted for 6,000 ft or better, you can overheat the engine by running at sea level. Too lean a mixture at near WOT can result in a significant power loss and a premature blown engine.

As far as additives go, the stuff we are talking about here (Stabil, Techron) shouldn't cause problems. I started using Stabil back in the '70's. Alcohol in the fuel during the winter could be a bigger issue. But the problems were mostly from methanol, which isn't used as an additive anymore.

dirtydan
07-25-2005, 12:35 PM
I use the boat on the Delta exclusively (at 26', 10'beam, 5000lbs dry - it's a bear to move). I bought the boat from a guy who moved it here from Utah. After it was already here - the guy put on a stainless steel prop (still relatively new). It's got a 1987 460 - and it runs pretty strong (330 hp) - but the issue of carbs/jets at altitudes got me thinking.

Should I be swapping my jets out or just adjust the fuel/air ratio? I was actually thinking about having the carb rebuilt . . . anything in particular I look/watch for?

Thanks again guys.
-DD

drstressor
07-25-2005, 01:03 PM
The adjustable jets are just the ones for low speed. They are probably fine. Sometimes they replace the high speed jets with ones with smaller diameters for high elevation. Other than Flaming Gorge, I don't think that there are very many high lakes in Utah for a boat as big as yours.

You could have somebody check the jet size. It is usually stamped right on the jets or else there is a number that you can look up and find the diameter of the jets. It probably wouldn't be too bad of an idea to rebuild those old carbs anyway. But if the engine runs strong at sea level, I'd bet all they did was to change the drive ratio to partially compensate for power loss and left the engine alone.

dirtydan
07-25-2005, 02:28 PM
Thanks doc.

Now back to your regularly scheduled program already in progress. ;)