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610 messages, Last post on Mar 17, 1999 at 6:57 PM

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#561 of 610 pinging vs. detonation by markbuck

Mar 09, 1999 (4:27 pm)

blight and stanford... here's my take.

pinging - caused by an uneven flamefront that propagates away from the spark plug towards the sides of the cylinder. Using excessively low octane fuel can result in compressive heating in front of the flame front with secondary flame fronts forming and causing the 'ping' noise. 'Low' octane fuel is more likely to burn unevenly when cylinder temperatures and compression is high and has something to do with more reactive sites on their chains of hydrocarbons.
Detonation is ignition from a hot spot within the cylinder head or piston before the spark plug fires and is very hard on the motor....

Guess these two definitions overlap as I read them.

I am not sure that burning rate is correlated with octane numbers. I have personal experience with reduced power using 100 octane LL aviation gas in 2-stroke motorcycles. Av fuel burns very slowly as it is designed for 2000 rpm air cooled aircraft engines.

I believe that you should run the minimum octane fuel that your engine will tolerate without ping. That fuel will produce the most power, best fuel economy, plus it's less expensive to boot.
Heck, I live at 7,000 ft and it's hard to get anything to ping up here no matter what the the octane rating. But when I tow in the low desert, I am very careful to run the minimum octane that the engineers at the factory recommend, or go higher if I detect a ping.

#562 of 610 stanford by stanford

Mar 09, 1999 (4:43 pm)

Well, I've done some more looking and I think that we're both equally wrong -- or as I prefer to think about it, equally right. Pinging is indeed caused by the multiple ignitions as you described, but is combatted by using evenly-burning gas rather than faster-burning fuel.

A great source of information is the gasoline FAQ.

A couple of excerpts:

  the octane rating of the fuel reflects the
  ability of the unburnt end gases to resist
  spontaneous autoignition under the engine
  test conditions used

  Flame speed does not correlate with octane

Doh!

#563 of 610 texaszach by texaszach

Mar 09, 1999 (5:07 pm)

Singer4 - Some posts back it was reported that the factory has responded to the bed height dilemma by mandating the two inch block as a standard production item. Can you get a clarification on this when you speak with the Ky. plant engineer on Friday?

#564 of 610 stanford - good website by markbuck

Mar 10, 1999 (12:08 am)

Here is more of the excerpt

The antiknock ability is related to the "autoignition temperature" of the
hydrocarbons. Antiknock ability is not substantially related to:
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons.
Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.)
Flame speed does not correlate with octane.

#565 of 610 moe7 by moe7

Mar 10, 1999 (2:21 am)

O.K. so which should i use in your opinion???

87 or 89? I live in New Hampshire and hate to hear any engine knock! I have been using mobil 89 octane gasoline.

moe7

#566 of 610 Tex.... by singer4

Mar 10, 1999 (4:21 am)

Yeah!! I'll be checkin' with Mark W. on Thurs. or Fri. Dlrshp in AZ is waiting on auth. kit for 2in drop...my first step...drop 2inches, then install hitch(Pullrite), then back it up under the 5th...see what the clearance is...if it isn't at least 6 inches...then the RV springs have to be flipped...no alternatives here!
By the way, just spoke to rep. at Pullrite...strongly suggest going with SuperGlide(400 # unit

$2200...best price I found)avoids the worry when turning---automatically moves unit back 18 inches, not just 9 in., and no need to get out and move levers!
Singer

#567 of 610 br1 by br1

Mar 10, 1999 (1:07 pm)

Just a overall height comment - I stopped and measured an F250 crew cab, 4x4, power stroke, auto, with trailer towing, short bed with LT265 A/T's and the overall height was 6'6". I also checked a F250 super cab diesel and an F350 crew cab V10 they were the same.

Note - someone put in numbers that add to 7' so something doesn't add up. I know this doesn't help with fifth wheel heights but I was concerned for garage entry (I have a std. 7' garage but door hangs approx 1 1/2").

By the way, how do you handle the "wait". I have a long way to go and am chomping at the bit already (just got VIN).

#568 of 610 stanford by stanford

Mar 10, 1999 (4:49 pm)

I wouldn't worry about the door -- do you have a garage door opener? The angled piece that hangs down is what would stop me from putting the truck in a garage if I wanted to.

The official height of my truck was 6'9". If its not exactly that (measured at the back of the cab) its really close.

#569 of 610 br1 by br1

Mar 10, 1999 (6:33 pm)

I measured the garage door (to the bottom of the width of the garage door) at 6'10". I have a double wide door so the "angled piece" I think you spek of is in the middle (between the wifes car and my truck) and doesn't come into play. The dealer also stated 6'9" but the trucks on the lot are not quite that high. As long as that is a max I'm completely happy. I guess I can nickname myself -"hate scraping swindows".

Thanks for the info.

#570 of 610 kcram by kcram HOST

Mar 10, 1999 (7:15 pm)

br1,

I am the Ram 3500 owner who measured his truck for stanford. My Ram stands exactly what the book says it does - 77.5". Assume that as your suspension settles, you may lose as much as an inch of height.

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