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Grade of Gas

3660 Views 28 Replies 17 Participants Last post by  HandOverFist
I know, I did read the sticky. It says the 5.7 is tuned for 89 and can run fine on 87, however, I was reviewing the manual and it says recommended for optimum preformance to use 91 octane.

So I was just wondering what everyone is using for their 5.7? I was planning on filling up with 87, I just wanted to be certian that this will not effect the engine in anyway.

Thank You,
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There is such a wide variety of fuel that premium one brand runs worse that regular of another.

Try to find the least ethanol content and use gas stations that do a lot of business, as the gas is fresher and has less chance to absorb moister.

The 5.7 can run nicely on 87 but if it detects any kind of pre-detonation event, it pulls massive amounts of timing to protect the engine. That seriously degrades performance and mileage for a short period of time... unless it happens more often.

The "hemi" head provide pretty good performance, but the wave front of 89 octane is petter for it.

There are so many production variances that one engine will run just fine on 87, while others will not.

My personal experience in ~40,000 miles is that I see fewer drivability quirks running good quality 89 octane. But not all 89 octane is the same. There are may here that are happy with 87 octane.

You may want to run 91 every once in awhile just for the cleaning additives.
 

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Click on the link below to watch a 20 min video. CBC did a documentary on which gas is better. According to this video, 87 is good for most engines even if they say premium is required. Like Coldcase said, go to a good gas station to ensure you get what you pay for.

We have always put regular gas in my wife's Acura even though premium is recommended. She has close to 200,000 KMs and so far no problems.

http://www.cbc.ca/marketplace/episodes/2012/11/pumpfiction.html
 

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There is such a wide variety of fuel that You may want to run 91 every once in awhile just for the cleaning additives.
I've been told by multiple sources (some working on the chemistry side of the oil industry, specifically for Sunoco) over the years that this is a fallacy.

First reference I could find using google was:

http://chemistry.about.com/od/chemistryarticles/a/which-gasoline-to-buy.htm

Gasoline Factors That Matter
The quality of gasoline and the additive package usually affect the rate of engine wear more than the octane rating. Basically what this means is that it matters more where you buy your gas than which grade you purchase.

Regular Unleaded Gasoline
The recommended gasoline for most cars is regular 87 octane. One common misconception is that higher octane gasoline contains more cleaning additives than lower octane gas. All octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against engine deposit build-up. In fact, using a gasoline with too high of an octane rating may cause damage to the emissions system.
Here's another good reference:

http://autorepair.about.com/od/enginefuelgasolines/a/highoctanegas.htm

Will Higher Octane Gasoline Clean Your Engine Better?
As a rule, high-octane gasoline does not outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.
Run the recommended octane to maximize power.

But don't run it under some mis-impression that it is "better" for your motor or fuel system.

EDIT - Boyvan - good link! saving that...
 

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Discussion Starter · #8 ·
This is awsome information, thank you. So I now know the 89 is recommended but here in Utah we have 85, 87 and 91. I have read in other forums as well and they were mentioning that the higher elevation states have the lower grade because it does better with the higher altitude. And again thank you all for the information. I put 87 in last night and will listen for any pinging.
 

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Air is less dense at high elevations. For normally aspirated cars this is going to reduce the amount of compression pressure that the fuel is subjected too because there is a smaller air/fuel charge in the first place. This means you will have less of a chance of compression ignition, which is one of the factors that higher octane is used to prevent.

Ergo, you can usually run a lower octane at altitude (which is why they usually have lower grades available than they do at sea level).
 

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run 87. higher octane is for power only.

if you hear a "pinging" from the engine - then up the octane to the next level. Its rare though that you really need it.. (I had a 68 camaro that HAD to have high octane..)
Thats old school, went out in the 90s. I had a '70 340 duster that would not run at all, let alone ping, on low octane fuel.

You will never hear pinging in a late model engine unless there is something drastically wrong. The engine computer automatically pulls timing before any detonation event. A driver won't hear of feel a thing, but the engine will run sub optimum, if you care.

I tune my off road vehicles as a hobby. The only way to see what the engine is doing is to put a monitor on it and look for tell tale events. The seat of the pants can easily be fooled.

There are numerous experts scattered about the web, many with agendas, some without. Perhaps my comment on high octane was miss understood. I was just trying to say that the only reason to use a high octane premium fuel once in awhile is perhaps for the cleaning additives. But as was noted, even the value of that is suspect.
 

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Cold, I don't know that all modern cars have a knock sensor.

I know for certain that most motorcycles and marine engines don't, so it's still applicable.

Sooo the rule of thumb remains...use the octane recommended by the manufacturer unless you hear knocking, then increase octane level.

But yes, if equipped with a knock sensor you shouldn't hear it. Though if octane is low enough you might throw a code.
 

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I know for certain that most motorcycles and marine engines don't, so it's still applicable.
All Fuel injected Harleys since... oh.. at least 2000 have pre-detonation sensors, and all HDs have had FI for a few years now. Thats a lot of motorcycles. My 1995 Ducati does.... just about any bike or vehicle with an engine computer and fuel injection senses pre-detonation in one way or another, usually not the old style knock sensors however. Waiting for the detonation is to late, damage done. There are many vehicles still out there with old style knock sensors, however.

Anyway the WK2 detects pre-detonation and adjust accordingly. You wouldn't know its working. It will throw a code only when the adjustments go out of range.
 

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All Fuel injected Harleys since... oh.. at least 2000 have pre-detonation sensors, and all HDs have had FI for a few years now. Thats a lot of motorcycles. My 1995 Ducati does.... just about any bike or vehicle with an engine computer and fuel injection senses pre-detonation in one way or another, usually not the old style knock sensors however. Waiting for the detonation is to late, damage done. There are many vehicles still out there with old style knock sensors, however.

Anyway the WK2 detects pre-detonation and adjust accordingly. You wouldn't know its working. It will throw a code only when the adjustments go out of range.
Uhhhhh NOPE, well maybe not a nope, but a bit of a qualified nope, you touched on it toward the end, but your statement is still too broad.

Harley does not use a piezoelectric knock sensor.

They DO, on some of their big twins, use a detonation logic where the ignition coil and ECM have some way of determining if it's going on. Some sort of feedback through the actual secondary ignition circuit (ION sensing, something to do with the ECM determining changes in resistance to the secondary ignition circuit that provide it info on knock).

But that logic is not enabled on EFI Sportsters (2007 to present).

EDIT - looks like you're right about when it appeared on Big Twins - I did some poking around and it looks like it debuted (supposedly first time used on any motorcycle - on the 2001 Softails with the Delphi EFI system)

I'd also have to check the schematic on our Ducati (696) but I can't remember off the top of my head if I've ever heard it ping.

I know most Moto Guzzis haven't used any system sensor based or ION based - as I've gotten all of th ones I've owned to ping (2000, 2006, 2013).

As for the WK2 I don't have a factory manual yet. EDIT I assume it uses a something more like ION sensing then? So IS there a code for prolonged pre-detonation detection/or long term timing retard - something showing the system is constantly active?

No matter - you are correct, that WHEN equipped with logic to deal with knocking it's unlikely the owner will hear it. We just disagree on the scope and breadth of what vehicles are so equipped. EDIT - but I could be wrong on the breadth now that I think about it. I guess if an ION based knock detection system may have become more common it would be harder to notice just from a wiring diagram, I guess you'd at least have to go through the trouble-codes, so you could be right, it could be much more common these days.
 

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I think we have a failure to communicate. :) You seem to keep wrapping your head around a knock sensor an that was not what I was saying. Knock sensors are old school. While I did not mention knock sensor, I was refering to what is commonly called a predetonation sensor or prediction algorithm.. Nothing like a knock sensor. Harley users a what the call an ion sensor system.... That is also used in many new sportsters. There are sure a lot of big twins out there, most of the bikes I see on the road are HD big twins.....

Bottom line is that, for the WK2, listening for ping and hearing none gives you false information.
 

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I think we have a failure to communicate. You seem to keep wrapping your head around a knock sensor an that was not what I was saying. I did not mention knock sensor, but a what is commonly called a predestination sensor or prediction algorithm.. Nothing like a knock sensor. Harley users a what the call an ion sensor system.

Bottom line is that, for the WK2, listening for ping and hearing none gives you false information.
My bad - I came back from a run and did some research. You caught me as I was trying to edit my post.

You might be right - or at least more right than I thought.

My switch from the automotive to the motorcycle and marine industries has left me a little lagging behind in that tech. I'm still seeing pezo knock sensors used, at least in the marine industry. I had forgotten about the Harley ION sensing systems on BTs (and didn't realize they went back as far as they do).

So you're right, it might be far more widespread.

That said, IF IT IS, that makes octane a much less important issue, since those systems are much more sensitive and better at preventing knock before any damage can occur. Yes?
 

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Harley users a what the call an ion sensor system.... That is also used in many new sportsters.
Well, a year or two ago, last time we checked into it on the XLforum that logic was NOT used in the Sportster ECMs. That might have changed by now, but I haven't heard of it.

Certainly I know for certain it was not used at LEAST 07 (introduction of the EFI Sporty - we have one) through 09 or 10.

I'd have to check with someone who has data-logged or gotten into the OEM maps of a later model to tell you for sure if it's still the case.
 

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I believe the reference to 91 octane in the manual is a mis-print...I seem to remember this coming up several times in the last year.

FYI, I run 87 exclusively...and average about 16-17 in normal rural driving and 20-21 on the highway for distances.
 

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Running the 87 at altitude is the same as running the mid at sea level. OP, you'll be fine. I lived in Denver for 7 years and even the dealers would say 85 is fine when regular was specified and 87 was fine when mid grade was specified.
 

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Gasoline is gasoline, and contains the same explosive power, no matter which grade you use. Octane controls the burn (flame-front).

Too little octane for that engine-type means the gasoline may self-ignite from the high temperatures in the combustion chamber, pressure of the rising piston, or a hot-spot deposit on the piston or in the cylinder. This is called pre-detonation (ignition before the spark plug fires). When the spark plug finally ignites, you'll have two combustion wave fronts. When the two wave fronts collide, you'll get knocking. The PCM will retard the timing, lowering your optimal performance. This happens so fast, you won't even know it.

Too much octane for that engine-type means when the spark plug ignites the fuel mixture, the flame front is so slow that your don't get a complete burn, lowering your optimal performance. This unburned fuel goes out through the exhaust, affecting your emissions systems, specifically your catalytic converter. Also, because the exhaust stroke of the 4 stroke engine doesn't completely evacuate the cylinder, unburned fuel molecules remain in the combustion chamber, and will be deposited onto the piston, eventually building up, raising your compression ratio, requiring you to burn premium gasoline to stop pre-ignition.

Higher compression engines create more pressure and heat in the combustion chamber, just before top-dead-center. That's where your power comes from. Remember 13.5:1 compression ratios that required 104 octane? I know - I'm old...

Engineers have designed their engines for a complete burn, and recommend a specific octane to accomplish that. It's that complete burn that will give you the most power and mileage.
 
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