[davepl]

I've seen lead replacement as well, but when Tetra-Ethyl-Whatever real lead was removed, all you could buy after that was a lead substitute, which really only even claimed to help protect valve seats, nothing with octane.

I think it's a safe bet that increasing the octane rating in fuel isn't cheap. I think another safe bet is that increasing R (Research) isn't the same cost as M (Motor). Forgetting for a moment which one is most important for detonation, you could probably increase the other by 50%, which increases octane ((R+M)/2) by 25% with no real benefit. So to expect something which can increase the octane rating of 20 gallons of base fuel, if it were cheap, it'd already be there and your little Chevron cars would be talking about it in TV commercials. Doesn't exist.

"As most of you on this thread seem to already know, but for the benefit of those that don't (TM-Dave)", increasing octane doesn't make a fuel more powerful, it just allows it to be used in an engine with a higher static compression ratio to extract more power with that higher compression. Increasing octane where it's already sufficient would only dilute the fuel.

Imagine that you could add water to gasoline to increase the octane. Would you want the 90/10 gas-water split or the 80/20 gas-water split? I'd bet you'd want the one with the most combustible fuel in it, subject to it not rattling in your engine. Just because (in our imaginary experiment) AV Gas was 70/30 wouldn't make it more desirable, unless you were at a high altitude or really needed it for forced induction or high compression. But your mom's car wouldn't go any faster at the track with it.

And lastly, in some cases, an aggressive engine management computer can (and many do) add timing until the engine rattles, then backs it off, and tries again periodically to increase it. Some keep long term averages. Some will rattle each and every time but pull out a different amount of timing in response to rattling. There are a number of different strategies, but here's the net:

- Many high end engines (new LS7, old LS-7, last-gen M3, etc) use compression ratios that could probably take advantage of up to some number like 93 or 95 octane.
- The old engines (1971 LS-7) will just rattle and fail without enough octane
- The new engines (2007 LS7, M3) will back timing off at a performance cost until its safe

But there is never, ever, as far as I can imagine, a case where an engine (in proper tune and without deposits) that was not pre-detonating and that wasn't computer controlled where more octane was -ever- better. Maybe if your grampa had dialed back the timing on your grandma's LS-6 you could return it to original spec with proper fuel.

And since this is a long post anyway, don't get me started with people who don't like the smell, or can't tolerate ethanol, or who think gasoline was just plain better in the olden days. I like the way my Dad's hardware store smelled on the spring mornings of the 1970s as well, but I don't claim his fertilizer was any better than current stuff, because I don't have any numbers to compare. But I'd like to, because I'm curious.

Unfortunately, the level of discourse on that topic can best be summed up in last month's Hemmings Classic Car editorial wherein we learn that gas was blue. Which is apparently a good thing. Which I was happy to learn, because our unleaded here (WA State) is also blue.

Where I grew up (Saskatchewan) farm gas was cheaper, I guess because there wasn't a road tax on it. So the farmers always wanted to run it in their cars and truck for going to town, but didn't want to get caught with "purple gas". So they'd put it in glass jugs on the porch until the UV rays of the sun bleached it out. And these were people with $200,000 John Deere harvesters, so I have no idea what lengths the poor people would go to... Actually yes I do.