I'm used to seeing a much smaller spread, like 10-30 cents/gallon, but I haven't looked lately as I haven't burned gas for a couple of years now.

On your Prelude, it could damage the engine if you run less than premium fuel in it. I'm assuming it cannot adapt to lower octane like more modern cars can. It sounds like your Civic can, and you might lose a little performance or hear some pinging, but for 80-90 cents/gallon, I'd try it out. Check with Honda's customer assistance line to see what they say.

I read in a car magazine 2-3 years ago that premium will yield about 3% better mileage than regular and eventually regular will be phased out. If the cost is close to 3% more, it's a draw. I might be mistaken, but I believe Chevron premium has more Techron than their regular, so there's other benefits. Many feel they make the best gas, I dunno.

^^^ That is how I feel about it also. The Prelude and the Civic have never had regular gas.
For the few cents extra...I feel it's worth it.

The Civic is showing 40 mpg or higher on every tank of Premium. That is worth it right there.

Certainly not for gold, and doesn't appear to be for fuel either.... not even close.

Gold @ 1200/oz mebbe 15 years ago - $50
At 1600 several years later - $100
Now at 1675 - $200ish

I think you'd have to get less than 33.75 mpg to break even with regular. I suspect you'd get closer to 39 mpg with regular, but you'd have to test it out to see. How many miles per year do you drive the Civic?

^^^ I took delivery of it in Feb of this year.
I currently have 7K miles on it....been using the Prelude a lot in the last month or two.

So, that's about 10,500 miles/year.

10,500/40 = 262.5 gallons. At $5.12/gallon = $1,344/year
10,500/39 = 269.2 gallons. At $4.32/gallon = $1,163/year

$181/year into my GoFundSteve account would be awesome.

^^^ lol...hey I'm almost 70...have to spend the money somewhere. SmileWavy

Here in Ct the delta is now $1. Not for me thanks.

If the car has knock sensors it's getting regular. That includes my Cayenne S and my Boxster S and
the many Porsches of all shapes and sizes I've had that had knock sensors with no problems.

My 997 and 991 cup cars? 100 unleaded just because

I'm not really sure what it costs, but a place around here sells non-ethanol 98 RON fuel instead of the usual 95 RON (premium) I usually use.

It may be placebo effect, but I'm sure 911 SC Euro with 9.8:1 compression runs better with it. Or more smoothly anyway.

Definitely go with Reg 😜

90c difference here. The GW wants 91 - but my choices are 87,89,93. It’s 13 vs 15mpg when you run 87 vs 93, and 7 vs 9 towing. Towing is worth it, regular driving - not so much.

Sorry, I wasn’t clear - I was referring to your Civic, not the Prelude (sweet Prelude, btw).

With a price spread that is typically at least a dollar, I only put 91 in a car that requires it. My 911 (Megasquirt, tuned on 91) requires it, so it gets it. My Saab (‘85 SPG) nominally requires it, but the APC lets it handle 89 just fine. My Fiat requires it (because turbo). My Sentra SE-R has an aftermarket ECU tune that requires. So goddamit, everything non-diesel I own requires the expensive stuff.

1998 Prelude has a knock sensor and I bet it retards timing if there is spark knock.

Probably not as fancy as today's knock sensor systems, though.

Around here, we essentially only have 10% ethanol (except 1 place). reg - premium is usually up around a $1. (maybe 80¢ or $1 or in between). Our gas is 87 89 93 octane. Honestly, I rarely even notice the cost of gas, so the difference could vary a lot or hardly at all.
Wow, aren't you fancy. Around Houston, I think there's only one gas station where you can buy ethanol free gas, Buc-EEs. We are 10% ethanol everywhere all of the time.
The regular to premium spread is around 90¢ ±20¢, and it's all 10% ethanol (I think last time I checked regular was ~$3/gal. At Buc-Ees where they have ethanol free gas, it's about $1/gal more than and only available at 91octane. I think everywhere else sells 93octane for premium.

The Prelude has 115K miles and it's seen nothing but Prem fuel.
Having the old style VTEC, it only kicks in at 4500 rpms...the newer VTEC starts at much lower rpms.

My 2010 Fit, with the newer type, I couldn't even notice when it engaged. The Prelude has a definite 'kick' with it. So I'm careful about engine knock.

Around here almost all the premium fuel is e0 and the other grades are e10/87 and e15/89, though some places have e0/87 and e10/87. They have raised the gap enough that the e0 does not pay for itself in the extra 2-3 percent mileage. Used to be about 3% difference on those.

The e15 is not always clearly marked and we have one car that specifically says no e15.

The only time I buy gasohol locally is if I am returning a rental car. On my many road trips, most states have no E0 options, and I just grin and bear it, and it runs fine. I have replace all the rubber hoses from the tank to the injectors, so I am not too worried about booze in my tank. I always calculate a stop about 450 miles from home to fill up with whatever, and arrive home with as little gas as I am comfortable getting. Then fill up with real gas the next day.

Back when my original 305 in the El Camino had 250K+ miles it started to rattle and I suspect spark knock when cold or under full load. If I used the middle grade of gas it went away. When I pulled the 305 with 300K miles on it, and put in the 350, no more spark knock, so it does fine on regular.

Every single gasoline vehicle in CA. runs on 10% ethanol full time. That's every single police car and taxi that runs around the clock 24/7, Every Charger Hellcat and McLaren or Ferrari, every Porsche including modified air-cooled, etc. And every motorcycle. I don't like that ethanol is required in our fuel, (reduces energy concentration slightly), but to fear running it is an old wives tale of the gear head set. It makes zero difference and actually is the easiest way on earth for refineries to add octane to gasoline. E85 would be an example of this.

We drive a hell of a lot more miles than people in the state of Oklahoma or just about anywhere else in the USA. That said, I'd love to be able to buy pure gasoline, (especially for fly-over prices), and grab it anytime I'm out on the road burning gasoline. That is rare, though, almost everything I own burns diesel.

For modern cars, yes. They can watch for knock and pull ignition advance when they see it. It means less power and efficiency, though, and isn't good for the engine itself. I think mine says it can run on regular in a pinch but it's advised to refill with premium ASAP, '17 Alfa Romeo Giulia.

Isn't ethanol less energetic, and has the effect of raising octane which reduces likelihood of knock. If you're going to have knock with 87octane 10%ethanol, you're going to have knock with 87octane 0% ethanol, right. So ethanol vs none doesn't really change knock characteristics for a given octane rating.

So whether running 87 or premium (91, 92, 93) it makes no difference if it's got ethanol or not (from a knock point of view).