Octane vs. Ethanol Content

[Nova Kaw 650]

I would say it would depend on how often you use your boat and how much fuel you use. I will add that are the gas lines updated to handle ethanol. If you go out every week and burn a tank or more the ethanol will stay fresh.

Look up phase separation. If you get enough moisture in the gas you will get phase separation. That can not be undone with additives after it happens.

For storage or intermittent use 100% gas and a cocktail of additives to fix carbon

The difference in 87 and 91 is how the gas burns. The higher the octane the slower it burns, burns cooler and resists preignition. There is not extra power in the fuel.

The benefit of 91 is comes from the engine. It allows for higher compression that would cause 87 to pre-ignite. It allows for more spark advance which increases burn time.

Well said. ^^^

[TYvII]

Ok so to further complicate the situation what about Verado that have knock sensors and can run 87 or 91 octane gas. I know for optimimum performance you run 91 but what is actually best for the engine? Thanks

[lpugh]

Ok so to further complicate the situation what about Verado that have knock sensors and can run 87 or 91 octane gas. I know for optimimum performance you run 91 but what is actually best for the engine? Thanks

Not complicated at all commonly, done in the auto industry since about 2000. The design is such that it will make full use of the higher octane with more aggressive timing curves, when detecting knock it utilizes a different timing table which will not harm the motor. However you will lose some power
As side note you can have most mercury ecms reflashed with a more aggressive timing curve which will then require 91 octane, but they cannot compensate for detonation
Mecury knew they could tune them 91 and they would make more power, they also know that many would run 87 in them and damage them thus we have 87 compatible motors
What would be the advantage building a 250 hp motor that runs on 91 when they can get 250 hp on 87.

[gehol]

In the Varado, the ecu can raise the boost to utilize the higher octane. Raising the boost has an effect similar to raising the compression. Either one increases cylinder pressure producing more horse power requiring higher octane.

[EuropeanAM]

In the Varado, the ecu can raise the boost to utilize the higher octane. Raising the boost has an effect similar to raising the compression. Either one increases cylinder pressure producing more horse power requiring higher octane.

Partially correct- SOME Verado models had this feature. NOT ALL Verado models were able to utilize or benefit from higher octane fuels.

[gehol]

Don, I just assumed it was understood that the conversation was about those Varados that TY was referring to, those that can benefit from higher octane.

[berudd]

There are many things that good Techs with years of experience with seeing daily in the real word problems will find solutions for. that eventually the manufactures will change their policies based on results we have learned in the field, just takes them longer to adjust than us. The problems with alcohol is a perfect example. It was found by the guys in the field not the factory guys

I do a lot emission system work on autos and I will say any motor will have lower Carbon monoxide and HC (hydrocarbons) with 87 vs 91 octane when Dyno tested. Notice the bold carbon
Carbon deposits are a very bad thing

That last part about emissions is interesting. Does that apply to higher compression engines that require higher octane? Also, lower carbon imply a more efficient burn? Just curious about this stuff.

[EuropeanAM]

Don, I just assumed it was understood that the conversation was about those Varados that TY was referring to, those that can benefit from higher octane.

MOST Verado engines utilized knock sensors. However, NOT all Verado models with Knock Sensors were equipped with multi-fuel "performance" strategies.

That feature originally showed up on the 275 Verado (which was later discontinued). Feature also came in some of the Verado PRO models... however, there were differences even in the Race Lineup (the 350 SCI, predecessor of the 350 Verado, didn't utilize knock sensors and required use of ONLY high-test fuel).

That last part about emissions is interesting. Does that apply to higher compression engines that require higher octane? Also, lower carbon imply a more efficient burn? Just curious about this stuff.

What would apply to engines with higher compression and/or timing strategies is that the fuel octane that MATCHES what the engine was calibrated with will burn most efficiently, with the lowest carbon emissions.

This is one of the reasons that you will hear folks commenting that they see a lot more "prop soot" on their Optimax engine when running fuel that's higher octane than what is required. Many find that reduces considerably just by switching back to the correct fuel.

Imagine how the combustion chamber, spark plugs, exhaust, and depending on engine type- Injectors, might benefit from considerably lower carbon emissions.

[SilverFox579]

Folks- this is pretty simple. Follow the above recommendation.

That means that you will use the octane specified for your engine.

If your engine specifies 87 Octane, don't run 91. Run 87.

Then look for the lowest ethanol content (never to exceed 10%).

Up to 10% ethanol content is perfectly acceptable in a top-tier, high-traffic fuel of the correct octane.

Can't make it any more simple...

Indeed.

[berudd]

MOST Verado engines utilized knock sensors. However, NOT all Verado models with Knock Sensors were equipped with multi-fuel "performance" strategies.

That feature originally showed up on the 275 Verado (which was later discontinued). Feature also came in some of the Verado PRO models... however, there were differences even in the Race Lineup (the 350 SCI, predecessor of the 350 Verado, didn't utilize knock sensors and required use of ONLY high-test fuel).



What would apply to engines with higher compression and/or timing strategies is that the fuel octane that MATCHES what the engine was calibrated with will burn most efficiently, with the lowest carbon emissions.

This is one of the reasons that you will hear folks commenting that they see a lot more "prop soot" on their Optimax engine when running fuel that's higher octane than what is required. Many find that reduces considerably just by switching back to the correct fuel.

Imagine how the combustion chamber, spark plugs, exhaust, and depending on engine type- Injectors, might benefit from considerably lower carbon emissions.

Interesting. The only pure gas I have access to is 89. Would not have seen that as being a significant jump but I do have soot in the prop which I was not really expecting. I've been running a mix of 89 pure gas and 87 E10. I think I'll go on steady diet of 87 E10 and see how it goes.

[EuropeanAM]

Interesting. The only pure gas I have access to is 89. Would not have seen that as being a significant jump but I do have soot in the prop which I was not really expecting. I've been running a mix of 89 pure gas and 87 E10. I think I'll go on steady diet of 87 E10 and see how it goes.

Try that with the Cocktail and you should see an improvement in the carbon levels noted.