Good question. As intelligently as I can, I will answer...

"I dunno."

But I'm betting you are right that he was sales and probably made the same interpretation of octane the rest of us did. (He seemed sweet, but he didn't blow me away with his technical knowledge.)

Does it help incrementally, though, to use high octane? Would it mean getting 39 mpg instead of 37 per say? Is there any comparison people have done that shows the cost/increase trade off? I don't mind paying 4-5% more if I'm getting 4-5% more mpg.

You certainly aren't going to hurt anything by putting higher octane fuel in...but the engine doesn't need it, so why pay the extra expense of it? If it had any positive effect, especially towards fuel economy (of a hybrid!), then premium would be the recommended fuel.



So does it change fuel economy? In a word, no. I'm sure there's lots of anecdotal reports that suggest there might be a connection. If it were a high compression engine and it required premium fuel to run effieciently, then that would be different. But the energy content of the fuel is the same...that's what counts.



For my other car...I use premium, because that's what is recommended. That said, I could still use regular, but the engine's controller would just dial back the fuel-injection if it sensed a "knock" condition under heavy load. This means I would have slightly less power. Would I notice it? Probably not in every day driving.



But in our car, we've got a nice big electric motor that takes up a lot of the load under acceleration...



What matters more is that the quality of the fuel is good...marginal fuel leads to excess carbon build up in the intake manifold, fuel injection, internal engine parts, etc. Use a good Tier 1 fuel with all the necessary addivites included already, and you won't need to worry about it.



Cheers!

How do you find out what fuels are good quality? Is there a list of Tier 1 fuels?

Isn't google great???

It turns out there's a site to answer such a question...toptiergas.com

From that, it shows which retailers are certified top tier fuels. Some are really surprising...kwik trip??? But the other usuals are there...Chevron, Shell, etc. but no Exxon!

TOP TIER Gasoline Retailers:

QuikTrip
Chevron
Conoco
Phillips
76
Shell
Entec Stations
MFA Oil Company
Kwik Trip/Kwik Star
The Somerset Refinery, Inc.
Chevron-Canada
Aloha Petroleum
Tri-Par Oil Company
Shell-Canada
Texaco
Petro-Canada
Sunoco-Canada

I tried GOOGLING... and I didn't find this!!!

This in formation is so useful I'm actually going to print it out and put a copy in our glove box.

5 second google search.........

http://www.toptiergas.com/retailers.html

You don't really want to use higher octane fuel than that the engine system wants. The reason is higher octane fuel will burn slower in an engine set up for lower octane, so you will waste some fuel (it burns in the exhaust manifold and cat). Your mileage will suffer.

Pearl is a
2007 Driftwood Pearl Prius
Package "B" (everything but leather, nav, and rear camera)

The higher octane will allow for spark advance to be full. Lower octane will reduce advance. (hence power)

However will the extra 8% cost of the fuel result in rasing the mpg by 2.5 mpg the way us light foots drive? I doubt it.

Consumer Reports found no advantage in using premium in cars that recommend regular. In fact, they found no advantage in using premium even in some cars that recommend it for optimum performance.

http://autos.msn.com/advice/CRArt.as...tentid=4024120

My wife's Passat recommends premium but if you read the tech specs in the owner's manual you'll discover that regular is also acceptable. I've run both and can't detect any worthwhile difference in fuel economy or performance but then I don't drive it hard either.

I'm still going to give high octane another try. We had our car filled with high octane when we got it from the dealership... and we had instant great results. We've pretty much been filling it with regular... primarily because of the commentary here... but it keeps tickling my curiousity to give high octane one more try.

It can't hurt... and it will only cost a couple bucks.