toying around with the idea of buying a well used Lexus IS250 AWD.

It has a "high compression" engine that requires, not recommends 91 octane.

So I start reading up on it a bit, because , well, if you haven't figured out, I'm so tight my shoes squeak when I walk, and I'm not interested in putting 93 octane for $50 more a month in a $10K car with 125K miles.

What I found in reading is that the crux of it is, lower octane fuel ignites more easily so in high compression engines, which results in uneven compression. To maximize power and fuel efficiency in a high compression engine, auto makers "require" premium fuel.

But any car made after 1996 has a knock sensor that retards the timing when knocking occurs and will do so continuously as long as knocking is an issue,even for awhile if you switch back to premium.

You'll find no shortage of people who swear up and down that you *will* damage the engine eventually if you burn 87 in a car requiring 91, but logically this Car Talk thread explains the fallacy in that.

https://www.cartalk.com/content/premium-vs-regular-1#4

Q. So, I should use high-octane gas to prevent pinging?


A. High-octane gas will prevent pinging.

But these days most cars have something called a knock-sensor, that will - under many circumstances - obviate the need for premium gas. Just about any car that's more recent than about 1996 will have a knock sensor.

Q. How does a knock-sensor work?


A. The knock-sensor uses auditory detection to actually "hear" the knocking or pinging. When necessary, it uses this information to delay the spark and to minimize knocking or pinging.

That's good news. That means you can use gas with a lower octane rating. And, if your engine detects a knock or ping, it can usually adjust the timing of the spark until the knocking is gone.

Q. You're telling me that modern cars automatically detect this problem, and therefore won't ping?


A. Right - as long as the load is not too great.

Load is the amount of work you're asking the engine to do, and it's affected by a number of factors, including climbing steep hills, pulling heavy weight, hard acceleration or driving in hot weather. Any combination of these factors can affect load. So, if you live out in the desert Southwest, it's 115 degrees out and you're hauling your mother-in law up, you're going to need premium.

Why? Because there's only so much that your car's knock sensor and computer can do to adjust the engine's timing.

Q. Is it a big deal if my car pings for a few seconds here and there, under these circumstances?


A. No, it's not.

Q. So, are there any circumstances under which premium gas would be a good idea?


A. If you plan to haul that aforementioned mother-in-law in hot weather, or are going to be driving up monstrous mountain passes with a heavily laden car, then you might consider filling up with a tank of premium gas.

Q. But, under most normal operating conditions, do I lose anything if I use regular unleaded instead of premium?


A. In many cases, no, but you'll have to experiment with your own car. If you take our advice and drive judiciously - without lead-footing or overloading your car - and you don't hear pinging, you can use regular fuel. Of course, you'll lose that warm feeling of giving oil companies an average of 20-30 cents more per gallon of gas. And, you will lose performance that under most driving situations won't be noticeable.

here is consumer guide, they have the same information but still conclude you should buy premium

-------------

As mentioned, it’s rare that new cars require premium-grade fuel, but two test vehicles that passed through here recently did—or at least, that’s what it said on their fuel doors. As both were Lexus models, we called the company to see what they’d recommend if someone accidentally filled one with regular.


According to Doug Herbert at Lexus, “Required” is a bit overstated:
Herbert said that both vehicles (an RC 350 sports coupe and an NX 200t compact SUV) will run on regular-grade fuel without damage. But since both the advertised power ratings and the EPA fuel-economy figures were attained using premium, that’s what they have to put as the required fuel. However, he also warned that continued use of regular-grade gas would cause the engine’s computer to back off on the ignition timing—thus adversely affecting both power and fuel economy—and that it would continue to do so for a time even after the car is filled with premium.

It’s important to note that Herbert’s advice only applies to Lexus vehicles, as he obviously can’t speak for other manufacturers—and we can’t, either. And while our stance is that you should use premium-grade fuel if it’s stated to be “Required” or “Only,” here are some thoughts if you accidentally fill it with regular.

Detonation is your concern, and as it mostly occurs under hard acceleration, tread lightly on the throttle. Listen carefully for the telltale knock or ping that indicates detonation, which means you should try and keep other noises (such as the radio or conversation) to a minimum so you can hear it. As soon as you get down to a quarter or half a tank, fill it with premium, which will raise the average octane level fed to the engine.

One more thing. Since premium-grade gas often costs about 20 percent more than regular-grade gas, some folks have thought of trying to save money by using a $4 bottle of an octane-booster product to raise the octane level of regular-grade gas to that of premium. Don’t even think about it. While we don’t want to make any blanket statements here, we feel pretty confident in saying that a bottle of an octane booster—even one costing far more than $4—isn’t going to raise the octane level of a tank of fuel by four whole numbers (87 to 91). Some brands may say on the label that they’ll raise the octane level by “3 points,” but that usually means tenths of a point—so from 87 octane to 87.3 octane—which is certainly not worth it. If you’re a manufacturer of one of these products who wants to refute that claim, please write to us; we’d be happy to eat our words to save our readers money.

But for now, the best way to save money is to use the lowest-octane fuel your owner’s manual says is OK, even if the fuel door “recommends” that you use premium. But if premium-grade fuel is “Required,” bite the bullet and put in the good stuff.

Do NOT rely on a factory knock sensor to keep an engine safe from detonation. If the car requires high octane because it has high compression, use the proper octane.

Using lower octane gas than what is recommended will be noticed! If the car requires 91 octane then anything less will ping, knock and maybe occasionally stall. You’ll probably quickly notice the loss of power as well.

If you really don’t want to buy premium gas then buy a vehicle that doesn’t require premium gas.

Is it possible to re-tune the engine to run with a lower octane fuel? With direct injection it may be possible.

I'm running a 2022 with a Super Charger, and I run high Octane or nothing....that's what the manual says, so that's what I do.

been using regular on my 2009 lexus rx 350 for 3 years , no problem so far

yea I don't think anyone is arguing a turbo or super charger shouldn't - the assumption is you are getting on it when driving and need that octane

naturally aspirated grandma cruisers - maybe not so much

Octane boosters are not worth it. Sure, if you light throttle around and dont pull any hills or steep inclines, you can run it on 87. Why chance it? If 91-93 octane is a deal breaker then you shouldnt buy the car to begin with. My 6.2 at4 requires 93. Its a little painful on fill ups, but would never run anything else. The factory GM computer is supposed to recognize lesser octane and pull timing, but it isnt a fail safe. Just run the proper octane or pass on the car. Best advice I can give

I don’t know much about octane boosters. Can you dump a can of that in everytime you fill up?
I’ve also read recently that gas will soon be 15% ethanol, which is sure to play hell with internal combustion.
Looks like Gunchamp answered my question as I was posting it!
7mm

If the computer will let a tuner in, yes. At a cost of power and most of the time, fuel mileage

I think the RX's are ok with 87.

nope, just checked, they say its 91

I also heard they are going up to %15 ethanol, there goes most small engines in America.

I had a Mustang with 5.0L Coyote V-8 and it was actually rated at two different HP figures for regular vs. premium fuel. The computer would adapt to either, but I generally ran 90+ octane in it. I did find that some stations had a much larger upcharge for premium than others, even though their prices on regular unleaded were comparable. I've also noticed that two Toyota trucks I owned with 24v DOHC V-6 engines really needed premium in dead summertime if I was pulling a trailer or putting any kind of load on the truck. They'd clatter otherwise.

Air pressure plays a big part in it. If you're over about 2000' in elevation, you can drop a couple points in octane. We're at about 3500'. All the regular gas in the area is 85. Go over to Boise which is about 2500, they all have 87. Boise is ok at 85 but many of the people there are regularly in towns farther west and into OR which is pretty marginal for 85.

i have a 2010 Ford flex 3.5(no turbo) that detonates like a mthr fkr at part throttle when the engine is cold or half warmed up(87 octane)... head wrench at the ford dealer scanned it several times, no codes, all systems fine... he says it cant ping as long as the knock sensor is working... Bullschit!...

If the engine calls for 91 octane, I'm betting you'll see better fuel mileage with 91 than 87. Maybe not enough to completely offset the price difference. But enough to ease the pain some at the pump. In other words, I bet using 87 in that engine won't save you as much as you think.

None of the owner's manuals in any of my vehicles specifically states, " use 87 octane". They state, "use at least 87 octane." I know that some vehicles specifically state to use 91 octane when towing but 87 is fine otherwise. I experimented with 91 octane for about a year and even though it isn't required in my vehicles there were modest gains in performance. The trucks would hold in higher gears climbing the same grades than when using 87 octane. If fuel mileage was any better it was nominal, and I couldn't tell it. But the gains in performance were worth the additional costs to me.

At least until gas prices went to $5-gallon last summer. Prior to that I could shop around and find 91 octane for only 30-40 cents more than 87. But after that it was as much as $1 more, and $5/gallon hurt enough.

In parts of the country above about 5000' elevation they sell 85 octane as regular, 87 is mid-grade and 89 is premium. I made the mistake of using 85 octane once. We filled up in NM heading into southern Colorado. My truck ran horribly until I burned through most of that tank. I went to 89 octane for the rest of or time in Colorado and the difference was significant.

My bmw mini has a supercharger, needs premium, and top speed of 134 mph.


I have had it up to half that speed.

My 2019 chevy with a 6.0 gas hs a tune in it to tow my fifth wheel, I can put reg gas when not towing or under load. Though I have found the gas millage and performance really suffers with reg gas. So I just run it on premium all the time and the performance and extra milage make up for they extra cost of fuel.

I have owned two cars in the past twenty-five years that had high compression engines and required 91 or higher octane. One was a '99 Olds Aurora, the other a 2013 Lexus LX570.

Both would run less smoothly with 87, and would trigger the dreaded "check engine light" within a few miles after filling up with 87.

The "non-ethanol" is getting harder and harder to locate.
Won't run that alcohol crap in any of my gasoline engines!
I can go further on non-ethanol than on the 10% ethanol.
Dollar for dollar, the mileage is about the same "price/mile", I just get more miles and better performance with the non-ethanol.

Non-al is too expensive here. I run it in all my small engines. I've tried it in the car but the increase in mileage doesn't even come close to offsetting the high price.

I just bought a 2022 big motor SUV that weighs around 6500 # , it has a 6.4 hemi that has 475 horsepower, this thing is nothing but a computer on wheels, with a price tag I never dreamed about spending, so why would I hurt motor or sensor’s running cheap gas and pay much more later in repair cost after high dollar warranty runs out.

My Summer Car is a 2010 Jaguar, it also required 91 octane,
I would always run off the top half of the tank, so I'd fill it with 94 then the next time 89, rounds out to be 91.5.
Never once did I run into any engine knock or poor performance.

High octane gas is 2400. Low octane gas is Unique. High octane gas is required for high compression engines because it give a slower, smoother burn than low octane gas. Low octane gas burns quicker but it hammers a high compression engine around when it ignites.

The info I see on the Lexus IS250 says that it's running 12:1 compression. Back in the old small block Chevy days if you ran 12:1 pistons a standard starter would hardly crank it over.

I don't know the answer for sure. But I would guess that 87 octane gas would be hard on a 12:1 compression engine.

It would be like pushing a 250 grain bullet to 1400 fps with Unique in a .44 mag.

THIS
I have run the gas mileage test many times.
Engines that call for 91 octane get better mileage on 91 octane.

I have an Infiniti I30 that requires high octane.
I sometimes will run a tank of regular, can't tell much difference. But 95 percent of the time I do use the high octane.

Didn't you crash your lawnmower? This might not be the ride for you.

This is a car myth. The reason why engine manufacturers specify high octane is ONLY due to EPA emissions and mileage mandates and nothing more. Modern ECUs can instantaneously retard timing to keep an engine out of detonation.

There are a brazillion YouTube engine dyno tests to prove the point.

A forced induction engine (turbo or supercharger) is another animal all together. Due to high pressure combustion, they need a higher octane. But for an naturally aspirated engine, as long as you don't need that extra 5 horsepower at 5,000 rpm, you nor your engine will notice any difference between 87 and 93 octane. But your wallet will notice the $0.30/gallon difference.

Now, if you compare 87 vs E-85, then there is a lot of performance lost/gained between the two.

I see about a 16% improvement on my 2.0 Ecoboost with premium, but that is confounded by the fact that around here premium is ethanol free. Well worth the $0.20 premium at Costco.

So, 10K for a lexus with 125,000 seems like a really good deal. Interior torn up or not; if maintained, they run for ever. But, lets run the numbers. An engine repair of $1,500 is 2.5 years of gas price difference. Keep in mind, Lexus are notoriously expensive to repair.

Assuming the $0.40 a gallon less expensive and the $50 a month variance, the annual mileage be between 10,000 - 13,000. So, for purposes of the thread, at 12,000 miles a year and MPG at 25 for premium and 20mpg for regular, the ANNUAL cost variance is less than $40. IF we use the previous comments of 16% as a baseline, yo are looking at less than $100 a year.

I feel certain that there will be $40 in increase damage to the engine.

Sometime back in the 90's, my brother had just bought an Audi A-4 or A-6 or some such, don't remember exactly. Soon afterward, he and I went on a road trip to Florida. He hadn't, at this point, driven the car extended distances at high speed. At some point, when I was driving, I noticed the temp gage climbing up there. Also, when we went to shut down, it would start dieseling a bit. He asked me what the problem was (my brother knows nothing about such things.) I asked what fuel he was buying. Answer was, "regular." I told him I don't claim to be an expert at this stuff, but I suspected that, in order to run on the regular, his engine system was retarding the timing a lot and, for some reason, ignition at that part of the cycle generated more heat than the cooling system could handle, thus the overheating and, with the overheating, the dieseling. Next fill up, he got hi test and the problem was solved. He later told me he went to his mechanic when we got home. I asked what he told him. "Some of that same stuff you said, about the timing and stuff."

I've also seen inboard/outboard boat engines that you couldn't get to shut down after running them hard until after they'd cooled down a little. Problem would go away with higher octane.

You can count on the engine ta detect and stop detonation.

*After* there's been detonation.

Ain't no "this things bout ta knock" sensor.

Just use E20, increased octane and performance and cheaper.

If it ain't available premixed, mix it at the pump.

2 gallons of E85 ta 14 gallons of 87, and ya got your 91, and cheaper.

wrong guy, I bought the hunnert dollar lawnmower, but never crashed one

Elevation vs octane

Here...GX 460 'requires' 91 oct

Rural Utah is at 6K' and up from here

Clear (eth free..readily available) 88 octane

Reg is 85

88 runs the GX great & delivers 20-21 mpg

Clear was $4.35/gallon last purchase

Oh yea......FJB

https://www.mikeshawsubaru.com/service/information/gas-octane-at-altitude.htm

You'd have to lower the compression ratio, but that would change engine performance, and defeat the purpose.

If an extra $5 a tank is a big deal to you don’t buy it.

Is Costco non-al everywhere? I'd love to pay their prices for my small engine gas instead of the high priced other game in town.

By the time you (or the knock sensor) "hears" preignition/detonation noise, the engine has been running on the ragged edge of damage for quite some time. Premium gas has the slowest burning rate of the three commonly available grades of gasoline, which acts like slow-burning "magnum" smokeless powder. Running regular gas in a "premium-only" engine is like using Bullseye powder in a 7MM Magnum rifle cartridge. Adding 5% Diesel fuel to mid grade gas increases the specific gravity of the fuel and slows down the burn rate. Pump one gallon of Diesel first, and top off with 19 gallons of midgrade- - - -saves money and prevents engine damage. Half a gallon of Diesel to 10 gallons of gas works OK, too. I once had documentation on 200+ dyno runs on various types of engines we built in the high school auto mechanics program I taught for 20+ years to prove that point.

I have a Lexus NX200t. I can't see any difference between 87 octane and 93. So I use 87. The dealer said that was OK but I might get a little more mileage with 93.

Good post

U ain't got Maverick ?

Eth free clear at them

https://www.maverik.com/

I have buily many motors. Drag raced for many years. Been through a couple years of auto tech. Trust me, high compression engines deserve high octane fuel. Dont cheap out. The modern computer is a pretty cool device and can keep an engine from blowing, but its not fool proof. And once again, the engine will lose horsepower and most likely fuel mileage by running 87. Dyno proved this in a 15 camaro i had. The computer had a chit fuel table built in when someone foolishly uses 87. Maajor loss in power

My wife had a 2011 RX350 and I am pretty sure high test was “preferred” which we lived by for the most part. We put 175K on it without issue. Her 2019 Infiniti QX60 requires high test so that is what we use too. If you buy the IS250, you need to feed it the proper fuel.

My FIL has an Acura that requires high test. He's put nearly 200K on it with regular. He also barely drives the speed limit. But he told me he'll never put premium in it. Can't argue with his success.

Do you have to over-complicate decisions??

It's really very simple: If you don't want to pay for premium octane gas don't buy a vehicle that says to use premium octane gas.

The gents that own cars that require premium fuel and want to save a few bucks by running regular, go right ahead. It’s your engine. Most cars will tolerate it under most driving conditions, but do your own research, and not least, keep a record of fuel usage. You’ll use more of the cheap stuff, and get less performance while doing it. Different additive blends in premium vs regular may also mean more carbon buildup in HPDI engines running regular fuel, never a good thing for performance and economy.

Like this, mine was a 63 SuperSport Midnight blue poly.

You can't tune the need for high octane out of a modern engine, and could only
marginally do so in old ones.

You took advance out to keep it from knocking, but that was probably because
you were running a lot of advance. If you had high compression, retarding timing enough to eliminate knock was going to leave you with a bad tune.



7mm.
Ethanol has its commonly known problems, octane isn't one of those.
Ethanol raises octane a bunch. The Demon 170 100hp Dodge makes requires E85
to get the 1000hp. It can't do it on "normal" gas.
But, the gas we buy won't have higher than listed octane. The boosters in the
additive package all gas gets are expensive. The gas from the refineries has a lower
octane, calculated so that the ethanol brings it up to the claimed number.

When we first went the ethanol blend, the 93 in the system was still 93,
when it was loaded at the rack their would be some 87 mixed in to drop the octane to 93. Sheets uses the same principle for the cheap ass 91 they sell as premium.
Can't remember the amount, but it's line 15% 87. Good money for them, selling 87
for fifty cents extra. And few customers realize that they aren't getting what they think they are paying for

.

Don't look like a 63.

Dunno. All I know is that the premium coming off the tank farm in Poky is all ethanol free.

1966 Super Sports had the wrap around tail lights.

what happened after 175K ?

I have 2009 RX350

65 Impala SS's had round tail lights and the wrap around trim... i think? Evening Orchid was a one year only(1965) color, and very rare...

similar has probably already been set here. but I have an 08 Dodge 2500 with a 5.7 hemi somewhere in the book and under the hood it recommends premium fuel of 90 some octane I don't remember exactly but it runs just fine on 87. if you put the higher octane in it does run better and get about one and a half to 2 mi to the gallon better and definitely pulls a load better. but the fuel mileage alone generally does not cover the extra cost but it gets close. if I know I'm going to be pulling a lot with the truck I start putting higher octane fuel in a tank so ahead of where I'm going to use the truck under a heavier load.

Octane booster is a scam. A typical bottle will raise the octane in a tank of gas by a point or two. That doesn’t mean it turns 87 into 89.

It means it turns 87 into 87.2, you’d need a five gallon bucket of octane booster to make a meaningful difference

Then I apologize.

I do like that you at least at it you’re a cheap ass. 😂😂 most won’t admit it.

Wifeys Accura runs on mid grade, can’t use the cheap stuff

I run premium in four of my six cars, two are 70's "muscle cars" and two are a Porsche and an Audi, both turbocharged. They will all see premium fuel.

That's interesting. In Idaho Falls the premium at Costco and most other stations has 10% ethanol. There's only a couple of places that have premium ethanol free. Some mavericks have a mid grade ethanol free but I've been skeptical of maverick gas. I go out of my way to find ethanol free for all my small engines. The place I usually find ethanol freeran out recently so I filled my gas cans with the maverick mid grade e free stuff. So far my mower has been running the same as ever.

When I was trying to decide between the gm 6.2 gasser and the 3.0 diesel the dealer told me that premium is recommended for the 6.2 but not required. He said he runs low or mid grade all the time in his 6.2 but thinks it might get a bit better mileage when he runs premium. He told me this same story of how modern engines can adjust themselves a bit to the fuel you use but said it can lower your power output and your mileage to not use premium when recommended.

Bb

If we gots one People here, we's good

whats going on with that house in the background? Looks like the owner loves adding additions

Older Ford Coyote engines have 11.5 compression ratio. The newer ones have 12:1

All are "flex fuel". They run fine on 87 octane. I run mine at 93 octane. Much better millage and power. But, I think the flex fuel engines have "special" electronics as far as timing control.

Back in the day, my '70 Cuda had 11.5/1 compression ratio. It HAD to use premium gas. I put Sonoco 260 in it when I could find it.

91 here is corn free. YFZ is getting a 12:5:1 piston in it this winter, Wossner states it's ok on pump but would run 91 as "pump" not 87.

I run 87 in the Taco but now am curious. I'm about due to fill up, probably Friday as I head to the races. I'm going to do a tank of 91 and see if there's a change at all. Truck's been pretty steady of a 21/22 mpg average for the tank with mixed driving.

My wife has a RX 350 it runs great on 87. I run 91-93 on some long trips and it gets over 30MPG .

If it calls for premium use it .

It will not make a bit of difference on mileage .

If a man is opposed to spending a few hundred dollars more a year to power a premium compression/performance engine.

He should buy a brokedick compression/performance vehicle and put brokedick gas in it.

Like guys putting 5 year old brokedick gas in a chainsaw and bitching the brokedick gas messed up their chainsaw.

Probably not but we'll see. Can't hurt.

In 2011 bought a new Silverado with the 6.2 premium gas motor and started running 89 octane gas when my inlaw, who managed the emergency division for the tollway, said all their trucks and wreckers had the 6.2. and they ran on 89 octane gas with no problems. Tollway would put out a bid every couple years for the cheapest priced 89 octane.

that's too much dick talk for me to read

Always some DA wanting to cut corners! Gets lots of folks dead in the aviation industry!!

People who run high compression pistons and/or cylinder heads without understanding why they are needed in some extremely rare circumstances are window-licking idiots. Unless there's an extremely radical camshaft installed to go with them, the fools are building an "almost-Diesel" that will break piston rings and detonate holes in the pistons in short order.

LSPI (Low Speed Pre-Ignition) has become a thing in current high pressure injection turbocharged engines, that the engineers are struggling to solve. High calcium content oils, and premium fuel seems to be their current recommendations to minimize the issue. Detonation on sudden wide open throttle at low RPM’s is very destructive, with cracked/broken pistons a common problem. So yes, if you’re running one of these engines that has forced induction and makes 100+ hp/liter, be my guest and try regular fuel. The knock sensor may save your ass, but then again, it may not………….

No brainer. If the manufacturers says premium gas and your can's compression ratio validates that, then use it. It's that simple. We have a last year of production Z-28 (2002, 35th Anniversary) that requires it and all we;ve ever used is 93 octane and once in a while 92.

Bought an Acura RDX for my wife to drive. 2.0 liter twin turbo four cylinder that produces 275 HP.

It only gets about 23 MPG out on the road. I don't know why they didn't just stick a 3.5 liter naturally aspirated V6 in it and call it good. I have a 2010 Acura TL with a 3.5 liter naturally aspirated V6 that makes about the same HP and gets better MPG.

Also, I don't understand why the twin turbo RDX requires high octane fuel. It's only 9.8:1 compression.

I recall the old days when people were putting turbos on those small block chevy engines that came from the factory with 8.5:1 compression. One of the big reasons was because 8.5:1 compression was about perfect for a turbo application and you could get HP out of them on regular fuel.

IIRC turbos boost the calculated compression ratio.

When the knock sensor retards the timing you've already had preignition. Buy premium if you don't want engine damage.

Another thing, all mfg. no matter what make you buy are looking to void your warranty for anything if it cost any big money, how do any of you that has new cars that have all this computer stuff on them say after 2018, are not throwing codes to mechanics when they hook your car up when you take it in with gas related repairs.

Supposedly to help address LSPI, the API recently published a new classification known as SN PLUS for oils, however, no one currently has a SN+ oil certified. Again, supposedly, BestLine claims their additives help reduce the risk. I use their products in every vehicle for $hits & grins.

I've never, in my life, had a gas related issue with any vehicle. (diesel gelling not included). I've had EVAP codes and I fixed those myself with a new gas cap. 12 bucks. Done - not warranty.

The code thrown would need to cause a technician to have the fuel tested for octane if the idea is 87 in a 91 causes the issue and not something else. I've never heard of a dealer doing that.

I don't even know if it can be done to a certainty.

Yeah, I've been running 93 in my cars for years. Current daily driver is a Saab with turbo and 5-speed manual. The book states "91 octane" but at the local Sunoco pump 93 is only 2cents/gallon more so that's what I run. The car gets mid-30's mpg highway (and is an absolute hoot to drive) so in the end I figure I'm not spending any more for gas than if I drove a mid-20's mpg car that ran on regular gas. If I drove a pickup or SUV that only got mid-upper teen's gas mileage I'd shoot myself!

I also have a vintage MGB with a high compression head, larger carbs & valves, and fast road cam. Of course I feed it a diet of 93 octane but on a sweltering hot day while hammering it up a mountain I get a faint whiff of knock, even after playing with the timing. No big deal, hammering up a mountain on a hot afternoon is a pretty rare occurrence, but I sometimes wish that Sunoco still sold 96 octane. Back in the day when I campaigned an MGA Twin Cam with 10.5:1 compression I burned nothing but high octane leaded in it, and I was probably the last guy to ever buy any of that stuff from Hess gas stations - I cried when they discontinued it.

I run 93 octane fuel in my 66 Fairlane. 302 engine 10:1 compression ratio

You oughtta hear all the gm guys running 87 in these new 6.2 engines, then they complain when their engines fail.

most folks dont have a clue what their compression ratio actually is... especially on the old school stuff... unless you do your own engines and measure everything yourself, you dont know!... most of them engine builders are full of schit... and most old school Muscle Cars were rated higher than they actually were... so most guys claiming that they run 91-93 octane with 10+ to 1 compression are just guessing... old rule of thumb still holds true... 87 octane safely supports 8.7-9.0 comp, while 91-93 octane safely supports 9.1-9.5... of coarse, new electronically tuned multipoint fuel injected stuff can get away with more...

Frontal area and drag coefficients are vastly different. I’ll bet if they both had the 4 cylinder, the TL would be leaps ahead instead of just marginally better.

BEAUTIFUL car Sbrown!! Wow!

My previous Audi (supercharged), current Audi (turbocharged) and my Porsche (turbocharged) all see premium as do my Mach 1 (427) and Dart (360). The others don't.

I burn premium in everything.

Get delivered 500 gallons.

My Wife's daily driver is a 2009 Lexus RX350 and we run 87 octane fuel without any issues.

Toyota 5.7l’s are designed to run 87oct in the tundra and cruiser. Diesel otherwise.

I had a C5 Corvete with 5.7L LS1 engine. I could not run standard grade, and even on mid grade octane it would ping a bit under load. It ran well on high obtain.
Nice car, but a classic money pit.

Non ethanol comes only in premium locally, so that's what I run, in everything that uses gasoline.

No ethanol in any engine of mine, Not ever.

Communist mandated watered down crap.

I bought a 2021 Ram with the 5.7 engine..There was no octane label on the fuel door and no mention from the dealer on what to run on it. I put in 87 and it ran fine for about 2k . I was visiting my brother and had to take him to an appointment and while sitting there broke out the owners manual and it said 89 . I filled it up with 89 next tank and noticed not one bit of difference in performance, mileage etc. In short if the owners manual calls for 89 run 89.

Won't repeat it and it is from experiences gained at least 65 years ago, but somewhere back there is a detailed post about octane ratings, octane blend pumps (Sunoco in the late 50s), and the use of tetraethyl lead as ICC (no longer available as such) - all gained while working R&D in a refinery. When a kid, the reason hot rodders were working to increase compression ratios had to do with higher performance in certain situations - had nothing to do with normal driving. Such increased compression brings challenges - pre-ignition being a big one, and spark timing can become quite critical. Fuel aspects of such control were expresed in octane language.

Repeated pre-ignition eventually will cause damage. Modern engine tech has compensated for a lot of the variation in available fuels, sensing control and component timing being prime. Yet, prolonged operation in such "adjusted" conditions can still bring problems. The earlier comment about heat build-up in the sensor retarded Audi is an example.

There always is a price to pay for enhanced bhp performance - usually at purchase, some in fuel and some in mechanical terms. If you like using it - buy it knowing that. If one simply likes impressive data about his ride, it may not be worth the cost.

KWFA,

You ask some really stupid schit.

LOL

I run 93 in my countach. I can’t read Italian, so I just play it safe. You should see the sparks fly when I let her rip with the studs on

Yes, it is possible up to a certain point - specifics depend on engine-type factors, especially when computer issues come into play.

Seems completely impractical to do so by reducing compression ratio - earlier suggested by another poster.

I haven’t read through all of the comments and I’m not a car guy. What is the intent behind building engines that require high octane?

It’s obviously generally more expensive vehicles but not necessarily high performance sport car type vehicles that require it. What is the purpose of a high octane gas engine in a non high performance luxury sedan?

Turbo charging is one issue. It allows the engine to have smaller displacement and thus higher efficiency during routine operations, and still have lots of additional available power when you step on it. So improve fuel economy, but need slightly more expensive fuel.

Higher compression ratio requires a more knock resistant fuel ie higher octane. Higher compression generally results in higher power/performance.

My man has spoken!



Corn is for making feed, not chit gas that'll wreck the carbs on your old trucks!

Nothing but the best for the beast…

👍

Is that a Malibu? Sweet car.

Wasn't someone on here talking about how to get the alcohol out of gasoline?
....but is it worth the effort?

In a normally aspirated engine, what re-tuning method do you use to lower the compression ratio?

That's a big 10-4!

I don't know, I wouldn't do it. You'd need to put a spacer or something between the block and head (to increase fixed volume), longer cam chain/pushrods and whatever else resultant problems there would need to be addressed. My response was more to identify the issue and broad treatment rather than any practical way to address it. I'd just use the recommended fuel for it or not buy the vehicle in the first place if getting the correct fuel was going to be problematic or too costly.

Same here.

Hahaha!

Shrapnels crate would run on 80

But, do they bring you Slim Jims and your favorite brew?

Had two Acuras that "required" 91 Octane. I used regular instead.. out here 91 oct isn't 20 cents or so more 'a gallon',
its more like 60 to 80 cents more a gallon...

but using regular, gather I'm not that hard on the gas pedal. Never was an issue and I'm the type that will listen for that type of thing happening in an engine.

Out west here, all we can buy is crap gas anyway....

have paid for high octane, " non ethanol" fuel ( as high octane is the only way to get it ), and just running it in my lawn mower. Lawn mower starts missing and I take out the carb and look at it, and it has water in the bowl.

So you pay for high octane, non ethanol, and what they give you is lower octane with ethanol in it... and they get away with it. This is in states ran by DemocRATS.. what possibly could go wrong? were busy "saving the environment" their way..

to avoid ethanol, I've gone back to the old upper midwest use of "HEET" in the gas thank, to prevent winter icing.
But it is soaking up the water that ends up quickly in ethanol.

This is a pain in the ass to me.. since I grew up with VWs in college, which would run on anything and you never had a problem. Nowadays I pay for a gallon of gas, of what I use to pay to fill my entire gas tank.... and all we can get is schitt fuel, regardless of what the octane is suppose to be. out here they sell ya what ever they want and get away with it.

Rather you would replace the pistons.

I would love to have a lift in my garage (and a high enough ceiling to use it)

The quickest way to reduce pinging is to retard the spark. This will also reduce your power . Kind of a no win situation.
Newer vehicles usually say for best performance use premium fuel. Not required but if you are going to run it hard or pull it hard put in premium. My 6.2 chev and 6.4 dodge both said this in the operators manual. These were 420 hp and 485 hp.
I’m sure some vehicles require premium. Edk

Caprice.

Wah wah... ahwah wah wah wah wah... yeah yeah little --- ...

It was a long time ago, but when we were building/gearing/tuning for various racing situations (or even just the fun and experience) we had the luxury of buying straight Sunoco 260 at the pump - no octane rating worries. Then too, there were exotics and nitrous. A different world.

When I bought a truck last year I was looking at the GM 6.2 but when I researched it and saw they recommended High Octane I went with a.5.3.
The 5.3 will pass easily going up steep hills towing my heaviest trailer.

I run 50 Cetane (typically) in my diesels... and an additive.

I am convinced the cost is offset by the savings.

Smoother power... IMHO

I fired up the pressure washer today (been sitting with old fuel for a YEAR).

Pumped out the old fuel...

Added ethanol free 93.

She was pissy as hell for 5-10 minutes (as she flushed the bowl and de-varnished)... THEN RAN LIKE A TOP.

FUEL FUGGING MATTERS...

Amazing "some folks" don't get this.

Wifey had a BMW that had to have premium fuel, was expensive

I dunno, maybe, if that could be done to reduce the compression ratio, probably comes with other issues to solve. Why bother, just use the correct fuel in the first place.

Just to be clear. I asked the question because it seemed incomprehensible that someone would state the idea of undertaking mechanical engine alterations to reduce cylinder compression in order to avoid pre-ignition.

A custom tuner can adjust the knock sensing parameters of the ECU ta avoid all knock.

But that would just mean the engine wouldn't have the power expected, on occasion.

And ya ain't gonna know when that occasion is.

Pre-ignition and knocking are 2 different things. Pre-ignition happens before the spark, knocking occurs as a result of the spark.

I did not see anyone question those aspects, although they could. Cause and effect are not rare in these discussions. However, one could debate your comment there about spark being the cause of knocking, but not worth the effort. Ponder - combustion/detonation prior to top of piston stroke?

Pre-ignition is caused by something other than spark igniting the fuel, could be carbon or lead build up that creates a hot-spot and acts a bit like a glow plug.

Knocking or pinging is related more directly to incorrect (low) octane rating fuel, which is how this thread started. You mentioned pre-ignition so I responded to that. Other issues can cause pre-ignition while using the correct octane fuel.

For a time I lived in Durand Mi., was near a small airport. Yamaha XT 500 was my ride to work most days( 57 mi one way).
Occasionally would stop by and grab a tank of av gas, for the 100+ mi. trip.
Noticeable difference in felt horsepower,w/ no long term damage, of course as I said occasional fill ups, then some sumbitch stole it off my front porch!

buntingmiester

Above, you posted that "knocking occurs as a result of the spark". If by "spark" you mean the firing of the spark plug in a normally timed engine, experience says that is not the case. The pre-ignition normally is driven by other factors (most of which can be controlled) and the ping/knock noise is produced by the nature of the pre-ignition (before spark plug firing).

In a 4 stroke engine, the sounds of pinging, or worse knocking, are caused by the uneven and sometimes violent combustion of fuel - sometimes referred to as detonation - before the piston has topped its intake stroke and started its down stroke. Desired fuel combustion is an evenly increasing/expanding flame front which exterts an increasing/expanding pressure force as the piston begins its down (pressure/power) stroke. Several factors can contribute to the pre ignition which brings about the ping/knock and detrimental physical forces affecting the mechanical components of the engine. Those are independent of normally timed spark plug action.

Pinging typically refers to the detonation that occurs in a remote of the cylinder as a result, and in addition to the spark ignition. Pre-ignition is a different thing all together and happens before the ignition spark.

I explained specifics of the pre-ignition process, and its distinction from the firing spark plug, rather thoroughly in the above post. Why then your attempt to re-explain it in odd terms - or a need to resort to that You Tube stuff?

What do you mean when you say that detonation "occurs in a remote of the cylinder"? Remote what? Is there supposed to be an area of the cylinder, remote from the combustion chamber, where pre-ignition occurs? Or, are you saying that the pre-ignition occurs in some remote area of the combustion chamber itself? Where is that "remote" of which you speak there?

You talk about pinging - must there be actual detonation to create pinging? Is there a functional difference between pre-ignition and detonation? What would be the difference between pinging and knocking?

How do you relate/explain creation of an octane rating and its subsequent effect on reduction/prevention of pre-ignition? Or, does it just affect pinging?

Your post seemed blessed with some confusion.

You'll need to speak to your mechanic if you are having issues understanding it. Maybe even look to see what might already be on the web.

Pre-ignition has nothing to do with the original post in this thread. You initiated the pre-ignition idea because you have no idea what you are talking about, figuratively speaking, or typing.

You’ll have to excuse him CCCC. English as a second language for him and everything doesn’t cut and paste very well through Google translate.

That’s a whole lot of words just to say “I don’t know.”.

It was a long time ago but I thought you could buy Sunoco 190 economy all the way to 260 racing fuel just by turning a lever on the pump?

Sunoco 106 was the most I ever saw at the pump. I used to mix it with Xylene and Marvel Mystery Oil to feed my Buick Grand National when I adjusted the wastegate to produce more boost.

I had a 63 Super Sport, Midnight blue it took ethel gas. Not mine but.

The single most bad assed color chevy ever produced. And car IMO

From late 50s onward you could buy a range of octane rated gas by turning a selector on the pump at Sunoco stations. Sun labeled them 190 through 260 - in degrees of 10 at slightly increasing prices.

260, the highest octane concentrate was stored in one tank, and 190 was the basic gas stored in another. The pump blended the two accordingl to selection. I was a HS kid working a summer job in R&D at the Marcus Hook refinery with the engineers who developed and were assessing performance of that blend pump. I ran quite a bit of 260 in those days.

The problems with understanding your posts will never be solved by any mechanic. There are a lot of knowledgeable engine guys in this thread. Not one of them can make any sense from your posts.

At first, I asked something rather vague because it looked as though you did not know what you were posting about, but gave you the benefit of the doubt. From there you simply replied with fakery and stuff you tried to repeat from the internet. But, you bungled that info and gave yourself away. You have not sensibly answered a single tech question that was asked of you in this thread - not one.

One classic example is your comment "Pinging typically refers to the detonation that occurs in a remote of the cylinder as a result, and in addition to the spark ignition." That gobbledygook seems inexplicable, and you declined to even try to explain what you wrote. Then, you are vapid enough to claim that pre-ignition has nothing to do with the OP.

FAIL - proof of fakery. Your pants are down around your ankles.

It is no wonder that the folks over on the prayer thread express such disdain about your trolling. Over there you try to fake being a knowlegeable atheist, and those folks eventually noted your silly shtick. Over here, you blew your cover immediately. I know some smart and very ethical young kids who know better than to spout fake stuff in order to seem important. Seems like your parents missed giving you that lesson.

Evening Orchid... Unique and Rare... But, bad assed?... no, just no!... love me a 65 Imp SS though... 409 or 396...

My BUILT 57 Chevy barely got by on Sunoco 260. On a hot day I had to keep the RPM's higher to prevent PINGING.

The pretty blue car that recommends premium gas gets it. At a couple thousand miles a year it costs me about $100 more a year to fill up with the non-ethanol good stuff around here. Given that Holden won't be making any more rebadged Monaros any time in the immediate future that's cheap engine performance insurance for me.

Well you are wrong about many other things, so it's no surprise that you'd be wrong here too, and defensible about it.

You give no answers to those key questions - but offer another of your empty defensive attempts to deflect from the embarrassment you brought to yourself in this thread. A pretender, you like to accuse, but that does not work because you don't know wrong from right.

Although completely defensible, my posting in this thread is simple and needs none. Those questions revealed your fakery and all here have seen it. Try the prayer thread some more - those guys may be more mauser9mm tolerant.

Death once had a near-Chuck-Norris experience

Longest 2nd gear in the history of 3 on the tree. Was it the original 283 that was built, or did you go to another block/heads?

You are on the mark. For the oldies here, I simply went to using av gas to protect them. Well worth it.

You unnecessarrily brought the irrelevant pre-ignition idea into the conversation. If you are that old and confused, and indignant about it, maybe you shouldn't be driving a vehicle on public roads. Just saying.

🤡

Sure he does.

He just doesn't know shat from shinola.

Somebody at Fort Sill like my wheel covers, they stole them.

For classic muscle, high octane and non-ethanol (with a stabilizer) makes sense. Like trplem eluded to, there’s only so many miles put on a toy.

My experience with my 2020 Gladiator (factory recommendation for high-octane) is it sounds like a sewing machine at idle. Sunoco 96 rectifies that. Would I be eating up my piston caps if I ran low octane and pushed it a lot? Maybe. But so few of these new cars die from internal failures anymore. Ancillary mechanical issues, ECM and sensors are what do you in these days. A darn airbag can total you.

To the OP, if you don’t push the car for performance and value money as much as you say, go 87 octane. My 2 cents.

My '97 Saab 900 turbo needs 87 octane minimum.

You just can't stop showing your crass idiocy, can you? You should have quit when you had only soiled yourself once. Now you are repeating the crapola.

If you think that the matter of pre-ignition is not germane to the OP and that a discussion of needed octane rating does not involve that, you have revealed your total ignorance of the topic. Even in that ignorance, you were compelled to jump in and make irrelevant nonsense posts - apparently trying to look important. No one made you post in this thread - you pulled your own britches down. Congrats on the poor show. Have you learned yet?

2012 RX350 was designed to run on regular gasoline, and I'm guessing the previous few years were too. 2013 RX350 specified premium (and I think all subsequent years do, too).

Good comments and advice.

You are just as wrong as ever. I corrected the error in my wording above.

I'll bet you sometimes have trouble remembering which pedal does what but will write a few paragraphs describing the excuses that you have in your defence.

No, my wife has a 2022 and it runs on 87.

Wow - you corrected one among your multitude of errors, but the other guy is wrong. That is rich.

Your vapid posting is getting weaker and weaker - soon you will run out of senseless ad homs and then what to do? You simply run to Google or You Tube to copy and paste stuff - ever seeking some mere significance.

My bike only has two pedals and they both do the same thing. Try some other "bet" - you will be a loser at that as well.

It's probably the safest thing for the community that you don't drive a vehicle anymore - your belligerent ignorance could easily lead to a dangerous situation. I just worry for the day that you appear in police Axon body cam footage on the Donut Operator channel.

What a nerd - try to change the subject and run an ad hom to deflect from your self-embarrassing posts in this thread. So you saw Axon on You Tube and you want to pretend that you know all about it. Make the internet community safe - don't post again.