I always seem to get slightly better MPG on Premium fuel than on 87. None of my vehicles require any more than 87, but the only explanation I can come up with is the additives and blend in the Premium. I've never really noticed they run any better. One other possibility is that I typically get fuel at discount stations & convenience stores. A lot of their fuel is generic from the terminal. When I buy Premium, it's usually at major oil places like Shell, BP, Texaco, etc., and I'm sure the over-all quality is better. I avoid the 89 Super (E10) because it reduces my MPG enough that my cost per mile is better with 87.

I think there is some truth to the notion that fuel quality differs and can make a noticable difference.

 

Ethanol sucks. It has less BTU's(energy output/potential) than regular gasoline and it takes more energy to produce it than it puts out.

 

Dude...who are you kidding...it may have less energy potential but you can make much more horsepower due to the cooler burn and flame spread and superior octane rating. That is why guys are tuning to run e85. Do a little googling. e85mustangs is one site or google Steve Shrader's "Brightmare"....Vortech 4.6 on e85 running 136 in the 1/4. Many other examples...it's the current performance fuel to run.

I know that my truck is MUCH faster when on e85.

 

I have been looking around threads for more info, and definitely a big debate on this subject, I own a 89 F-250 with 5.0, I've added long tube headers and an intake but aside from that (at least that I am aware of, I am the 3rd owner and the truck had sat for 11 years and I have pretty much gone through everything from the front to back of it) it's all stock, it's a great truck, here's my take on the fuel debate, sorry if it's a wee bit long, but this is just my opinion and experience, I have only owned one vehicle newer that a 1989, mostly because I can fix anything on them at home and they save me a truck load of money not having to put them in the shop like my wife's 2016 Acadia...... ugh lol

My truck absolutely HATES anything under 93 octane and absolutely loathes Ethanol, I starts hard, (normally I just tap the ignition and she would fire right up and idle clean and solid) idles rough, stalls out bad, misses, knocks, trash for power, (pulling a hill with no load is at best around 40 mph at 2500 - 3000 rpm loaded down is even worse from 65 to 30 mph very quick and that's with the pedal on the floor) I put 89 (nearly all of which contains some degree of Ethanol) in it once cause money was tight, aaannnndddd very quickly regretted that decision, and it would seem, the poor engine took some damage, still has a knock from the #8 cylinder rod or lifter, I'm pretty sure valves are going have to be replaced, very defined phu sound like there's a burnt out or close to burning out exhaust valve/valves and or valve seats, and from my experience, older engines are not tuned for Ethanol, it wasn't very dominant back in the day, most fuel was Ethanol free and so, engines were not built or tuned for the use of it, (not saying some of you fine folks dont have issues with it, but in my experience I won't touch the stuff with older engines, it will destroy them I had the same issues with my 63 dodge 330 with a carbed up 318, it wouldn't run for nothing with ethanol infused fuel and ultimately I ended up having to completely overhaul the engine due to burnt valves, pitted cylinder heads, warped rings and burnt valve seats,)
now I have heard that E85 is amazing fuel, (personally I am extremely skeptical about this claim with older engines, I think I'd rather spend the extra money to just put full on race fuel in my truck, we have a couple places here that sell both E85 and 101 octane) my 63 loved 101, and every couple tanks I'll put a gallon in before a full fill in my truck if I'm headed off to get firewood or hit the mub bogs, and up to putting Ethanol in it, I never had a problem with it, so naturally I am beyond hesitant to put E85 in it, perhaps there were modifications made to the engine I am unaware of that is causing this issue, increased compression or something of that nature that requires to higher rating causing it to spontaneously combust in the cylinder out of timing ( I know this can cause catastrophic damage to an engine) perhaps one of you with more experience has an answer to possible causes or something I should look over, and maybe it's all in my mind and the matrix is messing with me 🤷‍♂️🤣🤣

 

I have been looking around threads for more info, and definitely a big debate on this subject, I own a 89 F-250 with 5.0, I've added long tube headers and an intake but aside from that (at least that I am aware of, I am the 3rd owner and the truck had sat for 11 years and I have pretty much gone through everything from the front to back of it) it's all stock, it's a great truck, here's my take on the fuel debate, sorry if it's a wee bit long, but this is just my opinion and experience, I have only owned one vehicle newer that a 1989, mostly because I can fix anything on them at home and they save me a truck load of money not having to put them in the shop like my wife's 2016 Acadia...... ugh lol

My truck absolutely HATES anything under 93 octane and absolutely loathes Ethanol, I starts hard, (normally I just tap the ignition and she would fire right up and idle clean and solid) idles rough, stalls out bad, misses, knocks, trash for power, (pulling a hill with no load is at best around 40 mph at 2500 - 3000 rpm loaded down is even worse from 65 to 30 mph very quick and that's with the pedal on the floor) I put 89 (nearly all of which contains some degree of Ethanol) in it once cause money was tight, aaannnndddd very quickly regretted that decision, and it would seem, the poor engine took some damage, still has a knock from the #8 cylinder rod or lifter, I'm pretty sure valves are going have to be replaced, very defined phu sound like there's a burnt out or close to burning out exhaust valve/valves and or valve seats, and from my experience, older engines are not tuned for Ethanol, it wasn't very dominant back in the day, most fuel was Ethanol free and so, engines were not built or tuned for the use of it, (not saying some of you fine folks dont have issues with it, but in my experience I won't touch the stuff with older engines, it will destroy them I had the same issues with my 63 dodge 330 with a carbed up 318, it wouldn't run for nothing with ethanol infused fuel and ultimately I ended up having to completely overhaul the engine due to burnt valves, pitted cylinder heads, warped rings and burnt valve seats,)
now I have heard that E85 is amazing fuel, (personally I am extremely skeptical about this claim with older engines, I think I'd rather spend the extra money to just put full on race fuel in my truck, we have a couple places here that sell both E85 and 101 octane) my 63 loved 101, and every couple tanks I'll put a gallon in before a full fill in my truck if I'm headed off to get firewood or hit the mub bogs, and up to putting Ethanol in it, I never had a problem with it, so naturally I am beyond hesitant to put E85 in it, perhaps there were modifications made to the engine I am unaware of that is causing this issue, increased compression or something of that nature that requires to higher rating causing it to spontaneously combust in the cylinder out of timing ( I know this can cause catastrophic damage to an engine) perhaps one of you with more experience has an answer to possible causes or something I should look over, and maybe it's all in my mind and the matrix is messing with me 🤷‍♂️🤣🤣

 

Most folks, when arguing whether to use higher or lower octane gas in their vehicle, or whether fuel additives that boost octane really help kinda miss the point about what makes premium gas actually premium....If you go to Mobil's web site, or Exxon or Shell , and I'm sure any of the other major petro-chemical companies, You will find that each company has a variety of additive packages for each of their respective brands and categories of fuels... octane level is only a small part of why my trucks run better when I put premium fuels into the tank. Two of my Ford trucks ( an 87 F-150 short bed and 2004 F-250 XL...) have easily surpassed the 300,000 mile mark with original engines/drivetrains . My Lil Ranger ( 2003, XL w 4.0 4x4) is shooting for the 200,000 mark, and I've lost track of my old 89 Crown Vic, which isn't mine any more, (my cousin's husband has it now...) but was over 350,000 when he got it... I'm a stickler for preventive maintenance and using premium gas ... not because I want to produce increased power, but because all the additives in that premium gas cleans and lubricate the internals of those engines,... premium gas decreases varnishing in the intake tract, lubricates injectors from the inside out... and a whole host of other unseen benefits that only and engineer could ever know and love... I've been driving Fords for the last 45 years...I take good care of them, and they repay the kindness... Using premium gas is part of that care and maintenance

 

Octane does absolutely nothing to make "more power" Period. End of story. If you're not getting detonation (pinging) on 87 octane, putting 91/93 in it is literally tossing money in the garbage.

Engine Masters just did an A/B test on the dyno, on a much hotter engine that any stock pickup engine, and it makes ZERO difference. I don't know if the video is out for anybody that's not paying for a MotorTrend On Demand subscription, but unless you've got detonation issues, don't bother.

 

These are always interesting discussions and, like with most things, the exceptions don't make the rule. We know that octane is simply a rating of the fuel's ability to resist combustion through compression. Premium gas has the same amount of joules, or calories as regular gas, the same energy content. I know people who feel their vehicle runs better, gets better fuel economy, etc., on premium over the regular fuel their engine is rated for. I wonder if one of the conditions that may provide that result is with computer controlled engines controlling ignition advance. They can optimize the ignition timing while the engine is running and some vehicles will respond enough to return better consumption and run characteristics. That makes sense to me and because every situation is different it is possible for some vehicles to respond differently than others of the same year, make and model. As the saying goes, "your mileage may vary".

 

There is a distinct difference in the way EFI system in these trucks operates compared to more modern vehicles that directly relates how the engine responds to fuel octane. Newer motors have a more sophistocated spark advance strategy that constantly searches for the maximum amount of ignition advance to apply and fuel octane can affect how much that is, because higher octane fuels have a higher flashpoint they produce more detonation resistant in an ICE so more timing can be applied and that will produce more power. In these trucks the total amount of timing advance is preset and is referenced to the base timing setting at the distributor, and these motors don't have any way to detect detonation so without user intervention to manually add base timing the motor won't automatically take advantage of high octane fuel. That means the motor can be setup to better perform with higher octane but that also means it would then ping badly if regular gas was used.

 

I know people who's illnesses go away when you give them a sugar pill but that doesn't mean that a sugar pill makes them better.
I'd put dollars to doughnuts that you can't reliably measure a difference between good 85/87 and good 91/93 in an engine designed for regular.

It's a pretty common phenomenon that when people pay more money for a thing they tend to think it's better. How else can you explain BMW ?
The science on petrol is pretty well understood.
You've got a mix of dino* juices with cocktail of additives that do a variety of things.
Buying an octane rating over what your engine is designed for will not improve performance, UNLESS you've got some other issue that is causing preignition, aka: knock.

Change your spark plugs, wires, button/rotor, coil, O2 sensors, oils, filters etc. (Do a tune up). And see if you get better performance, at least those things actually make a difference!

.*fyi: typically plant matter, not dinos but dino juice is fun to say.

 

That is exactly right, the science is clear. The reality is that the manufacture and operation of our vehicles is not an environment of scientific control, there are tremendous amounts of variability in the real world to cause the odd situation to fall outside the expected, or intended parameters. I understand and expect that an engine designed to run on regular fuel will perform as intended and expected on regular fuel. I concur that if it does not perform as expected, then that means something with the system is not as intended, or expected; compression, timing, etc., etc. Around here the premium for Premium is 25 - 30 cents per litre, which would mean around $18 - 20 per tank, on my truck. I can get an 8 pack of my current favourite IPA for that, so that is where I'd rather put that money. I'm confident in knowing what the beer will do for me, so no need to run higher octane fuel in the vehicles. However, if someone wishes to experiment with higher octane fuel I will raise a hoppy glass, wish them well and look forward to hearing the results.

 

As stated above, higher octane fuel doesn't have more energy or btu's, but is more resistant to burn. Only time that should come into play is if an engine pings/detonates on lower octane, then higher octane will usually improve or eliminate that condition - which in turn does make engine run better. Newer computer systems will pull or advance timing (as mentioned above) to accomodate differences in fuel octane level, which may or may not create a noticible performance difference.
I like my carb'ed 460's initial timing set at about 14 BTDC. By doing that they will ping (especially in hot weather) on 87. 91 seems to mostly alleviate that. Since they rarely get driven anyway, I leave timing there as they are slightly more responsive at part throttle than if set at 10 BTDC.

 

Have you looked at re-curving, or modifying the mechanical advance in the distributors? When I rebuilt the 351W in my 1970 XL I installed a mild cam, Performer intake, 4V carb and headers and the engine is happier with 14 - 15* initial timing, like your 460's. My distributor had 26* of mech advance and 40* is too much total mech advance. The plates in my distributor were 13 - 15 plates, unfortunately, not 10 - 13's, so I didn't have the opportunity to flip the plates to the 10 side, which would give 20* advance, instead of the 26* from the 13 side. There are limiter pins to stop the advance plate and I added some heat shrink to enlarge the pin diameter, which effectively limits the travel and reduces the advance. I can have the initial where it is better and keep the total in the 36* range which avoids pinging on regular fuel.

 

94ZR580 no I have not. Just laziness on my part. I have a dial-back timing light and haven't used that either. On my 92 460 still factory in an F250 it is happiest set at factory recommended 10 BTDC with SPOUT pulled. Tried 14 and then 12 but not as happy. The other two are both EFI engines converted to carbs in 79 Broncos. Those along with quite a few 400's I've had in the past seemed to run really well at 14 BTDC, just need the 91 fuel not to ping. Even the 92 if towing close to 12K in summertime is happier with 89 or 91. It also is getting close to 300K miles.
Thanks for suggestion, just haven't ever bothered to do that.

 

You sir ARE correct!