90 octane marine fuel vs. 93 w/ 10% ethanol

[bblueg]

For a PCM zr450...
price is within 10c per gal.

want to use the best fuel that 'protects' the engine AND allows it to run optimally.

Will the 450 retard using 90?
Yes, I can run stabil-marine but is that 'as good as' marine/rec. fuel?

[jsta281]

I don't know what marine fuel is but to answer is 90 octane enough the answer is maybe but there are many variables. Altitude being a major factor. The closer to sea level the more likely 90 is not enough.. Load is a big factor as well. If what I understand about the 450 to be true a hotter cam and hotter tune over the 409 suggests you should be running 91 at high altitude and 93 at sea level.

[biggator]

If I recall.. the last time we had this discussion - the dealers agreed that 93 off the street or 90/91 ethanol free were about the same. In my case, 93 off the street is cheaper than 91 non-ethanol on the lake.

[jsta281]

What is it about non ethanol fuel that makes the lower octane rating rmore knock resistant?

Ethanol fuels may result in poorer milage as it takes more to make the same power but ethanol also has a higher octane rating (for example E85 is 130 octane)

I would check octane rating on marine fuel before I just assumed it has equal knock prevention as a higher rated fuel.

[DanielC]

"What is it about non ethanol fuel that makes the lower octane rating rmore knock resistant? "
Difference in the rate of burn of the ignited fuel air mixture.

I do not know all the details on the ZR-450 engine, but if it has a catalytic converter, it will automatically adjust the amount of fuel to correct the fuel air ratio when switching from E-10 to straight gasoline. In either case. the engine probably also compensates for lower octane by retarding the ignition timing if the engine's computer hears any knocking.

In my experience, running E10 gasoline does not cause any problems, other than a possible loss of power due to the lower energy content of E-10 gasoline. but I tend to keep the gas tank full over the winter, and also use my boat usually three oe more times a week, starting about a month ago, and into October. My thought is I am running enough gas through my boat
that any water in the tank is eliminated in the normal running of my boat. I alos do not like in an area with high humidity, and high heat.

On the other hand, if you live in a humid climate, and only use your boat every two weeks or so, and it sits for longer periods of time, with a not full gas tank, it is possible you could accumulate enough water in your tank that it would be a problem running E-10.

I have also heard that if you mix the higher octane E-10, with higher octane non alcohol gasoline, you end up with a higher octane than either one alone.

[jsta281]

"pure gas" having a higher energy potential over E10 for any given quantity is a bonus for fuel economy and perhaps a quantifiable HP benefit. I however, don't believe that 90 pure gas has more knock prevention then any other 91 octane gas. With that said I don't dispute 90 "pure gas" may be better then 93 E10, but not because it has higher/better detonation prevention, but rather because the engine will probably run with more power and better economy even if the engine management system is pulling some timing as a result of knock detection. What I really think is that many people run more octane then they require thinking it is "better." However, in the case of the ZR 450 and the 550 having sufficient octane is much more likely to be a concern.

The only way to really know is to run on 90 "pure gas" and data log, to see if timing is being pulled to avoid knock prevention. If the answer is no, then there is no question that pure gas is a more efficient fuel. If the answer is yes, then Better go with some e10, or Torco (I've done my sales pitch on this stuff already). The reality is, with out data logging, you just can't know for certain what is going on. He could fill up with 90 "pure gas" never hear a single ping, and have it run good with no issues not realizing the EMS is pulling timing the whole time. It is also possible that on 90 it does not pull a single degree of timing (although I suspect that the 450 at sea level requires a min of 91 and most likely 93 to keep the EMS from pulling any timing but that is just a guess)

[shawndoggy]

octane and potential energy per gallon are different. E85 has high octane but less potential energy per gallon. Octane is just a measure of resistance to premature detonation (slower to burn / less volatile).

On the corn gas if there's a limiter I'd think it'd be the fuel pump's ability to deliver enough of the lower-potential-energy fuel to the motor to make stated HP. Pretty sure GM has gone to higher flow fuel pumps on e85 vehicles to address this issue. And of course you're going to burn more of the fuel to make the same power.

[bblueg]

Dealer and owners manual confirm that less than 93 will revert timing to a "protection" mode. Regardless if pure gas (marine/rec gas I have available at 90 octane). So filling up with 93 it is. I will just run stabil to counteract the corn effect.