91 OCTANE (BIG DIFFERENCE?)

[LJS30]

For that last two weeks I have switched to 91+ octane fuel in my 88 Mark 7. I was skeptical at first in regards to the extra power and less pinging which was supposed to occur. Well, I am no longer skeptical at all. My pinging has all but disappeared and I seem to have gained some extra power and life out of my 190,000 mile 5.0 HO. When these engines are brand new, does the 91 make that much of a difference? Or is it mainly because my engine has some serious miles on it?

[Nick]

When new, 87 octane was recommended. With age and miles, carbon buildup can cause heat pockets and thus pinging. You're probably experiencing that with your higher mileage engine.

[ekooke]

Sea Foam would be cheaper. smile.gif

[Bluegrass]

There can be a number of reasons.

Octane creep from combustion chamber carbon build up.

Colder weather causes the air intake to be denser resulting in higher cylinder charge that needs more fuel resulting in more power no matter the octane of the gas.

Gas additives are changed for colder climates making the gas a bit more volatile and evaporative for improved starting and vaporization.
The engine computer computes the resultant ignition timing from all these actions.

[MichiganTeddyBear]

yea, I agree.

What most people fail to realize or fully understand is, higher octane fuel actually burns slower, to reduce ping and detonation. therefore, unless you have an engine that can properly handle it, (higher compression, ignition timing), your not gonna see any MORE performance over 87.

yea, and seafoam is cheaper

[84mark]

well, it isn't any matter of an engine being able to 'handle' higher-octane gas- any engine that runs well on regular will run just as well on super without harm; you're simply wasting money...but conversely, an engine with higher octane needs, primarily seen due to higher compression ratios, will suffer both in performance and possibly in longevity from gas with insufficient octane rating...

[pro-five-oh]

quote:Originally posted by Bluegrass:
There can be a number of reasons.

Octane creep from combustion chamber carbon build up.

Colder weather causes the air intake to be denser resulting in higher cylinder charge that needs more fuel resulting in more power no matter the octane of the gas.

Gas additives are changed for colder climates making the gas a bit more volatile and evaporative for improved starting and vaporization.
The engine computer computes the resultant ignition timing from all these actions.


Clean your engine with Seafoam (or something like it, don't wanna sound like I'm married to Seafoam) and change the plugs afterwards. Odds are you'll never need 91 after that.

[LJS30]

Will do.

[Kit Sullivan]

quote:Originally posted by 84mark:
any engine that runs well on regular will run just as well on super without harm; you're simply wasting money...

Incorrect. High octane fuel in an engine not designed for it will eventually lead to far worse carbon deposits and pinging...the very problem you are trying to avoid.
Ford, GM and D/C have all made specific claims that high octane fuel useage in an engine not designed for it will void fuel system warranties.
Clean your system with something like Seafoam...it works great,is cheaper in the long run, and is the right way to combat this problem.

[Philip]

I've yet to experience an older Ford 5.0 without ping using 87 octane. Okay, so the manual says it's normal, but who wants to hear THAT. I always used premium in my '84 Cougar 5.0, the only way to avoid the pinging. No performance advantage that I could tell, but in '84 the V8 was only rated at, like, 140HP. (laughing) Like I'd have noticed anything with that. Ran my '97 4.6 Cougar with 87 and it was very happy and silent. My Mark requires premium, and I have yet to test the waters on that issue. There's not enough cost difference on a tankful to chance it on that complicated mess. Bottom line, avoid the ping but don't look for any real performance advantage other than a quiet motor.

[2manymarks]

I have had over a dozen Mark VII's and presently drive 5 or 6 on a regular basis. 95% of the time I use the recommended 87 octane and have never had any noticeable ping or preignition. Except for one, all are basicly stock. Most of my driving is in less than hilly terrain and I stay out of town and traffic lights as much as possible. I usually get 18-22 mpg in my LSCs and up to 24-26 in the 88-90 BB. Honest!

[Kit Sullivan]

quote:Originally posted by Philip:
I've yet to experience an older Ford 5.0 without ping using 87 octane......I always used premium in my '84 Cougar 5.0... No performance advantage that I could tell.... Bottom line, avoid the ping but don't look for any real performance advantage other than a quiet motor.

Well, I have three Mark VIIs, with anywhere from 90,000 to almost 200,000 miles on them.
I have an 87 Mustang GT, 120,000 miles, and I have an 89 E-150 with a 5.0 in it, well over 200,000 miles.
NONE of them ping...all run on 87 octane.

The fact that you claim you have ALWAYS used 93 in your Cougar only proves my point: High octane fuel used in a engine not designed for it leaves deposits, which leads to pinging!
And since you could not notice any performance advantage with the higher octane, you were clearly wasting your money.

Bottom line: Keep your engine free from carbon build-up, and run the octane it was designed to run on. Your engine will last longer, and you will save money on each fill-up.

[Philip]

I bought that '84 back in the day, but it was used, had 49,000 miles on it. That was my first decent car and I kept it maintained to a T. Used Regular for some time and began getting ping on long trips and hills. Switched to 93 octane and it disappeared. Always passed the smog test, couldn't have been too much carbon buildup I wouldn't think. My Grandparents had numerous Crowns over the 80's years and lastly an '88 Grand Marquis (now my "work truck") and an '89 Towncar. They all acted the same way. I think it has a lot to do with terrain (hills) and regional gas formulations have to come into play somewhere as well. Consumer Reports claims that using higher than required octane is wasted in the form of heat. But I hear ya on the performance and price thing: that old '84 had precious little performance when it left the factory and gasoline wasn't going to change that but it kept the engine from rattling, and when gas got so high this summer after Katrina, that required premium for my '98 Mark was painful, but had to have the stuff regardless. You've gotten some serious mileage out of your vehicles. That's getting your money's worth. Good show!

[MichiganTeddyBear]

I don't think carbon buildup in the cylinders will affect emmisions too much, unless its really bad and really screws up the flame front.. you would likely even get pinging on 93 if it was that carbon fouled anyway.

you want a cheap way to help increase power??? its not a 'big' increase, but it does help a LITTLE... and is free, or nearly free! But it is a lotta work, takes a lotta time, and is a royal pain if the heads are on the engine... Index your plugs.. I don't know the exact placement of the ground electrode for max performance, and it varies by engine type, but it has been proven to add a small percentage if all your plugs have the ground electrode in the right place. Helps out on the 'flame front' thing too. Ya gotta remember, the air/fuel mix don't all burn at once when the spark ignites it.. it travels from the plug outward, and the shape/size of the combustion chamber, as well as plug placement in chamber, effects how the mix burns. (wow, what a run on sentence!)

[Bluegrass]

There are some other things that happen to these engines.
The undersides of the intake valves can accumulate carbon deposits upsetting the fuel entrance pattern. This carbon comes from among other things the intake of oil from the PCV system as the engine ages as well as deposits from the gas.
The EEC has no sence or ability about this for correction except what the oxygen sensors detect for air-fuel corrections fed back to the injection control. Usually the introduction of oil into the air-fuel mix results in a lowering of the final combustion octane. This by it'self could cause light pinging below the level of 87 octane fuels
Since the EEC calculates the final ignition timing and has the ability to change the spark and fuel tables over a plus or minus 10% range, there can be a drift in direction of the table values vs the actual physical conditions that exist.
Remember that the Speed Density system is a computer model program worked out for the engine design with allowences for minor changes that occurr.
This just shows some of the short comings of the EEC programing and hardware of the times.
The later PCM control is much better at this by several orders of magnitude.
The later ECM systems will detect any fuel that is out of spec more than about 10% for alcohol or octane content such as E85 fuels that the engine was not originally design to use.
The later control systems will detect the use of fuel other than 87 because the software method of tracking cylinder power contribution is very precise and based on a time base method therefore will detect a change based on fuel, bad spark plugs, bad coil, voltage leakage, valve seal and anything that causes a cylinder to fall outside the software 'EXPECTED' times built into the base programs tables "AND" modified over the long term by the sampleing process of engine wear, fuel quality and the like until or unless the ECM is powered down and results in rebooting back to base tables.
Very clever i'd say.
It is difficult to say precisely what caused the ping in any given 5L engine since it is usually load sensitive, subject to sensor tolerences, ageing process and the inital base ignition timing setting as well as fuel quality and time of year such as winter.
Well anyways i'm sure ya all understand. :D
Happy Holidays. ;)

[Kit Sullivan]

Carbon build-up in modern fuel-injected engines is one of the most prevalent problems that engineers face today. Many, many times worse than with a carbureted engine.
Tests have shown that in as little as 500-1,000 miles of driving with low-detergent, untreated gasoline that carbon deposits can result in as much as a 15% drop in economy. That's quite a difference.
As 'Blue' stated, the carbon build-up on the underside of intake valves is a big offender.
Almost all pinging on an otherwise healthy modern gas engine can attributed to carbon deposits. Running high octane to reduce the pinging is just a short term way to stop the symptoms, but in no way cures the problem.

[LJS30]

I still need to run SeaFoam in my engine.

[84mark]

where do you get seafoam?

when i changed out the head gaskets on my 86, there was a lot of carbon buildup on the pistons...i cleaned it all off, but i never thought about the underside of valves...why the carbon, and why worse with fuel inj...? and how can higher octane produce more carbon- all increased octane does is to raise the threshold for ignition so that it will only fire from plug spark.....? maybe you might mean that the higher octane gas simply permits the car to keep going despite the buildup, rather than that the octane causes it...

but i too have never had ping, or knock, in a 5.0, models ranging from 83-88...i did have a 3.8 from 83 that was notorious for it....

[88LSCinSW-FL]

I've been able to get SeaFoam at AutoHole and Advance. Not sure about NAPA.. never looked, and have only ever been in there once anyway.

I still need to change the plugs post-SeaFoam. Been running it way too long like that after the treatment. Also have to get some of it in my truck soon.. crankcase, gas tank, and vac line methods.. but that thing (like my Mark, pre-seafoam.. doh) just got plugs in it recently.

On a side note: This 91 octane you speak of is an oddity to me. We have 87, 89, and 92/93. (depending on station)

[Kit Sullivan]

Higher octane fuel requires more heat to burn thoroughly ,and burns considerably slower than low octane fuel. And engine that is not designed to use high octane fuel efficiently will leave a lot of unburned fuel in the cylinders leading to carbon deposits.
Think of the difference between trying to burn dry kindling vs. wet kindling. The wet stuff will burn, but slower and will leave more residue unless there is a LOT more heat and combustion going on than normal.

Modern engines are much hotter internally than the older style, which tends to bake fuel deposits quicker and harder than before.
When an engine is shut off, capillary action brings liquid fuel to the tips of the injectors and can drip, leaving more CDP.

[macx]

The only thing I notice on the popular Mustang boards is that
lots of guys say they pick up worthwhile power by increasing
timing to 14+ initial. They, then, of course have to use 91
to prevent pinging.