I've got a question that's been nagging at me and I can't find any definitive answer to:

1) I know that the higher the octane rating of the fuel, the 'slower' the burn so it actually makes less horsepower under the same conditions as a lower octane fuel.

2) Advancing timing will increase power output, but it can cause detonation problems; ie, why higher octane fuels can be needed.

My question: does bumping up the timing to just below ping levels on high octane pump fuel make more power than what is lost by running the higher octane fuel itself?

I'm going to be doing the 6 litre tuneup this next weekend when my coil, plug wires, and timing light show up. I plan on only running as high of timing as 87 octane will allow since all 89 octane here is E10 blend; while it's cheaper than 87 I loose more money in the mpg hit than I do in the $0.10 difference in price.

However, since I'm on a traveling construction crew, I'm living in a 5th wheel camper which I will only have to move a few times a year. At those times, I would like to run either 91 or 93 octane fuel (whichever I can be sure to find along my whole route), and bump up the timing for the trip to boost my power levels. I'm not too concerned about the higher cost of fuel for those trips since I'm only looking at 6-7 mpg as is, but a boost in power would be nice for taking off and climbing hills that I encounter. I would then knock my timing back down to run 87 after the trip.

I'm hoping I can bump my timing up to 12*-14* above base timing on 87 octane since I'm usually driving unloaded; how far could I advance the timing on 91 octane under load? Will there a big enough boost in power to warrant the time to mess with timing before and after pulling the camper?

Edit: Also, does anybody have any good descriptions of what I should listen for to identify ping? I don't think my truck has ever suffered from ping and I've never heard it before (as far as I know anyway). Will running my truck up to operating temp and then doing some hard accelerations be enough to identify ping or will I need to pull something heavy like my camper for a longer distance to identify pinging problems?

 

I have the 4.9 in a F150 4x4 Auto, and have been struggling to get the power it should put out. After owning it a year, and changing about every sensor, and a complete tune, it ran much better, but I have never heard a ping on 87 octane. It still has this initial hesitation until it would get above say 1500rpm, almost like I was dragging an anchor. I have always believed in setting everything at factory spec., and I did make a TPS adjustment to get .96V at closed throttle. That almost cured the hesitation. Today, I checked the timing again, and it was right on 10BTDC where I had set it last month when I tuned it.
Today, I decided to experiment, and went to 14BTDC static timing, and my hesitation is gone, I lost the boat anchor I was draggin, and it made a world of difference! And no pingging! Im leaving it there, because I don't tow, but I would bet something must be worn like timing gears or the distributer gear.
But in your case, I would say, go to 14BTDC and try it. I am glad I did!

 

I remember that a buddy and I checked the timing a year and a half ago when the bodywork started, and it was either 11 or 12* already. I had to order my own timing light to check this out this time since I've moved away from home. I'm really hoping to push the timing on 87 even further with the higher voltage coil and better wires I have on order. I may even have to run a few tanks of E10 89 again to see if I can offset the mpg drop with a higher advance timing since a by-product of the 6 liter tuneup is supposed to be slightly improved gas mileage.

 

Octane rating only has to do with the "stability" of the fuel, or it's resistance to spontanious ignition due to heat & pressure. The actual rate of burn being slower in higher octane fuel is a common misconception. Burn rate & octane are two seperate characteristics. In fact, some high octane racing fuels actually burn faster.....it has more to do with the fuel blend, additives, etc.. Here's a good article about it.........

Racing Fuel - Octane And Burn Rates - Stock Car Racing Magazine

"Pinging" will sound like marbles in a coffee can. You're most likely to experience it during high engine loads and cylinder pressue and temperature....like pulling a heavy trailer up a hill or WOT acceleration (even when empty). My recommendation would be to bump the timing slightly to maybe 12*-14* BTDC. You should be good on 87 or 89 when unloaded and use 91 octane fuel (with no Ethanol) when you pull your camper. That should give the best combo of MPG and power. Switching to a 180* t-stat may also help keep things cool and ward off possible pinging. A Seafoam treatment to clean any carbon from the chambers can also help lower the octane requirements if you are having issues. If you want more power for towing, the best options are improved exhaust, cam, heads, gears, etc..

 

You can keep pushing the timing until you start hearing pinging. You should be safe to run 87, and the base timing for our trucks was 10° BTDC, so don't be too worried.

Burning slower might be a myth, but detonations aren't, and higher octane fuel prevent that, that's why racing aplications use it, so they can advance the timing without hurting the engine by having advanced detonations. Higher octanes can also be compressed futher with minor risks.

 

I realize that I can keep pushing the timing, but is it going to keep making more power? I'm asking because I don't know, but I thought there's only so much timing you can push before you also need to bump up the compression to see gains. I'm just wondering if I'll see a power increase on the low compression 460 by running a higher octane fuel and higher timing.

 

Higher cylinder pressure = more force = more power. The higher the compression ratio, the more power you can produce. Think of ignition timing as more of a tuning technique. The point is to adjust the ignition of the fuel mixture so that complete combustion and peak cylinder pressure is achieved at precisely the perfect point in the stroke process so as to exert the maximum amount of force on the crankshaft. This point is based on the angle of the rod & position of the crank. By advancing the timing, you start the ignition process earlier. Most engines will experience pinging when you start to advance the timing and approach close to this "sweet spot". Hense, higher octane can allow you to achieve the advance required for MBT. The actual amount of advance required depends on the actual engine design. If you can actually get to this point, advancing it further will only hurt performance. Where this point is on your engine....I have no idea.

 

OK. That makes sense. So essentially, 87 octane, when tuned to it's maximum potential, might not be the maximum potential of the hardware in my engine. So to reach the advance I need for optimum power, I may need to upgrade to higher octane fuels. Thanks for clearing that up.

Now, is it safe to assume that on pump gas (up to 91 octane for instance), I can push the timing as far as I can before ping becomes a problem and still stay on the upward trend side of the power gains curve. I don't want to advance the timing too far and start falling backwards and making less power. I'm only guessing this is a possibility based on dyno pulls of motors on Horsepower TV (FWIW) and how they start to loose power when advancing timing too far, but most of their builds are more performance oriented than a stock 460.

 

On and unrelated note, Brian, do you have a bigger picture of truck in your signature?

 

on 87 octane and your low compression 460, you'll ping long before you lose peak power. it is possible (albeit slight) that you reach the point where you lose low-end torque in exchange for higher rpm power, but that really shouldnt be an issue on factory tuning and the particular motor in question. however, higher octane in an application that doesnt REQUIRE it, will cause a loss in low end torque production.

all that bein said, the gains achieved from running higher octane will not be worth it on your big 460. the thing makes gobs of power down low (relatively speaking), and thats where you'll wanna keep it. running higher octane will just drain your pockets faster, cuz if you push the timing to the point in which the higher octane will be a necessity, youll more than likely move the power band up in the rpm range for the above said reasons (also, the heads/cam cannot support power high in the rpm range). in addition, the gains will not justify the means. youll increase the pedal feel a good bit by bumpin the timing to a degree that 87 octane will tolerate, you wont work miracles by goin any further and increasing the octane (gains will be minimal, if at all).

moral of the story : tune for 87 and dont look back. you dont have a high performance motor, and 87 is what it likes.

you may notice that ive "timed" my 302 to run on 89 (pings on 87). "so '89f2urd, why do you not preach what you practice". . .the 302 is a joke, thats why. it needs to spin 3000 rpm to go anywhere, it cant tow anything even at peak power, and i dont care what the fuel mileage is (not my DD). that bein said, i'll take whatever i can get, and just keep the motor singin for help as i drive around.

 

I can't truthfully answer that.....Intuition tells me that the lower the VE of the engine, the better chance you have of going past the point, but I would GUESS that your engine will be "knock limited" before ever even achieving MBT timing. There are a ton of design and real world variables that effect all this, so it's really only something to be concerned about on a dyno or in a lab. Plus, once you get out in the real world and actually drive, you'd have to back the timing off anyway to adjust for differences in air, load, temps, etc.. The best thing you can do is play around with it and keep a timing light in the truck so you can adjust "on the fly" if needed.

Yeah, I have a bigger picture of the tag-axle F250, but I can't access Photobucket from work. I can PM you a pic later tonight if you want.

 

on the E10 blend, a higher CR than the 8:5:1 or whathave you is needed...Thats where your MPG is going...Wrong octane (A LOT higher than 87....IIRC, Ethanol runs around 120-ish...But is Alcohol based, therefore giving a cooling effect....And in a factory engine that uses heat for effeciency....Then it causes issues..)

So a set of pistons, shaving the heads, SOMETHING needs to be done to run it EFFECIENTLY on E10.....The higher CR, you'll retrieve some the peformance you've lost, and get it with cheaper blended fuel....

Just my .02...

If I'm wrong, someone please correct me...But ^ is my research findings....

That the alcohol based ethanol needs a higher compression ratio to burn EFFECIENTLY....Therefore is an asset in Forced Induction engines...higher CR, octane rating, etc.....

 

E10 (10% Ethanol blend) is typically 89 octane. E85 (85% Ethanol) is around 104 or something like that, depending on the blend. Pure Ethanol is around 113, I believe.
The biggest problem is that Ethanol blends contain less energy than pure gasoline (approx 15% to 20%)....so you'll never get the same fuel efficiency as a straight unleaded fuel, be it 87, 91, 93 or whatever. Consequently, the slightly cheaper price of E10 or E85 is usually offset by the increase in consumption. You also need to adjust the fuel map to burn E85 effectively. The performance potential for E85 is tempting, but there are many forced induction Mustangs, Camaros, civcs, etc. putting down incredible HP on 93 pump fuel.

 

D'OH....I was reffering to the E85 then....

E10 Sucks....Got it...

 

Exactly the information I was looking for! Thanks!

Looks like I'll stick to 87 octane and tune the timing there. I avoid 89 in both my Focus and my truck since both have proven to run cheaper per mile on the more expensive 87 octane fuel.

I guess I'll have to save up for headers and possible gear swap to get that extra bit of towing power.