Before you all go wild with the "repost" icons, let me just say that I've seen a lot of these threads, but not with this particular question, so forgive me if I missed something.

In my area, it's nearly impossible to find 92 octane fuel. Most, if not all, "Premium" fuel around here is 91 octane. The convenience store near my house has a deal that (with their little membership card) the "Plus" fuel, which is 90 octane, but has 10% ethanol, is the same price as the "Regular" 87 octane fuel.

Acura recommends 92 octane, which just isn't practical around here (I haven't found a station yet that sells 92 octane). That leaves me with a choice of 91 octane, or for about $0.20 less per gallon, 90 octane (87 octane isn't even a consideration, since I can get 90 octane for the same price). I have no problem with paying more for the recommended fuel, but that's not going to happen anyway, so here's my question:

What kind of difference am I looking at going with 90 octane as opposed to 91? I'm talking HP and MPG mainly, but also any other problems that could result in the lower grade fuel... not to mention any problems with using an ethanol mixture.

Now, I'm not looking for any "You have a $35K car, and you can't splurge for the good gas?" kind of responses here. If I could get 92 octane, I would, but I can't. I wouldn't have a problem spending an extra $3.00 per fill-up if that meant a 5-octane difference (like 87 to 92), but I'm talking ONE octane point here (90 or 91), and I'm simply trying to find out what benefits that extra $3.00 is going to buy, if any. I'm really looking for details here (the average MPG, HP, etc. difference I could expect), but I welcome all responses. Thanks.

 

I think its time to move....

j/k

I think the difference wont be too great, but you may lose a tad bit of performance, nothing to really worry about though

 

The octane of what's considered premium varies with location. In high altitude locations, cars don't need as much octane to prevent knock. It looks like you're in Kansas, though. I didn't think the altitude there was particularly high. In any even, just use what's sold as premium in your area, and everything will be fine.

 

The deal with ethanol is that you lose power irrespective of the octane, which would be slight or nill with fuel without ethanol.

The reason is that the specific thermal output per unit of measure of 10% ethanol fuel is lower than pure gasoline - what that means is that while ethanol raises octane, it produces less power. You will se ereduced power, and increased fuel consumption to travel the same distance. That is part of the big lie of ethqanol. It does lower emissions on a one-to-one basis (milliliter to milliter), but if one has to burn more of it to travel the same distance, has it actually lowered anything? The answer is highly doubtful.

remember that ADM is a huge contributor to Congress, and was particularly good at greasing Bill Clinton's political coffers. And ADM is one of if not the largest producer of the corn from which ethanol is made.

Ethanol fuels and re-fromulated fuels in general produce particularly nasty deposits, and if aftermarkets cleaners are not used regularly, fuel consumption and clean burn are firther degraded. More of the Big Lie.

If you have to use that stuff, run a bottle of one of the fuel system cleaners I recommended in one of my RR Journals entry in 3G Garage.

Hope this helps.

 

So, RR, let me see if I understand you. Are you saying that the difference between the premium fuel (without ethanol) and 90 octane with ethanol can be GREATER than the difference between that same premium fuel and 87 octane without ethanol?

If I switched to the 91 octane fuel (again, no ethanol in the 91 octane stuff), how much difference do you suppose it would make in HP and MPG? (I've filled up my car about 4 times now, and have always used the 90/ethanol fuel). If I could get even 3 MPG more, then it would actually be CHEAPER to buy the 91 octane fuel, so that would be a clincher. I don't like the idea of those deposits either. If I switched now, do you think I still need to run some cleaner through there, or is it too early to have done any significant damage?

 

I would just use 91. The Great State of California only has 87, 89, and 91 - so 91 is what I use and I haven't encountered any problems.

 

Use the 91 with an octane booster such as 104+ available at Pepboys or Discount auto.

High compression engines require high octane to reduce knock. Your acura will retard timing, but this is not operating at optimal levels.

 

do all fuel companies blend ethanol? (i'm in CA and seem to always notice the 10% by volume ethanol stickers).

 

Acura says to use 91 octane per my owners manual. Kansas has a higher altitude than most of the USA, so less may suffice. Alcohol will not lower power (O2 sensors compensate for fuel mixture and your power will not suffer), but will increase fuel consumption (about 4 %, or about one mpg less in mixed driving with 10% alcohol). However, alcohol increases the risk of getting water into your fuel system.

 

Yes, Acura recommends 91 octane, not 92. You're fine with 91.

 

That's not correct. Alcohol absorbs water into solution and allows it to be passed through the fuel system and out the tail pipe rather than settle in the bottom of the tank.

Gas line anti freeze additives like HEET are primarily alcohol (either methol or isopropl). We've used them for years in the snow belt to remove excess water from the fuel tank to avoid ice in the fuel lines.

 

Alcohol aborbs water but it apparently comes out of solution in some instances (temperature change?). Alcohol is added to the gasoline at the last depot to minimize the time spent in contact with water (water in pipelines). It is not piped with the fuel. It ships separately in stainless steel railcars to the depot. CT is stuck with 10% alcohol after the State banned MTBE, so we have seen a fair amount of press on the issue. The State ignores the fact the oxygenated fuels do nothing for modern cars, but politics and science never seem to mix.

 

This is not correct - it will lower power - alcohols do not provide the specfic output as does gasoline, and the O2 sensors cannot correct for that. You mention a 4% drop in MPG - why do you think that is? It is because the engine is usijng more fuel to compensate for reduced power. Your first phrase of the 3rd sentence is wrong, and contradicted by the 2nd phrase. How could a fuel system that has "compensated" and produces the same power increase fuel consumption?