[quote]ORIGINAL: mopartodd


I don't have the hemi tick and I'm jealous, so I'm trying to duplicate it with pinging. I realize the computer will reduce the timing IF conditions are right for detonation knock. If it's doing it on mine it's unnoticable. I still loose all steering control as I pull the front wheels off the ground at WOT launches.

 

Sorry guys if I didn’t explain my self good, my dad has a 05 hemi same truck as mine but red, he runs 87 in it since day one, he does not think that it makes a difference, I drove his truck around for about 2 weeks before I got mine and there is a little bit of a difference, and to touch up on my truck yes I do have the smaller tank, and I always get over 300, granted it is always freeway miles, but I only ran one tank threw it before I lifted it so I really don’t know if that is good or not.

 

very interesting post.... damn, im learning.................................

 

Mopertodd,

That info I did not know. Cool if it's accurate. How does it detect engine knock?

And your right, if the computer can adjust for engine knock and the engine is designed for 89 Octane, then 87 would make a difference in power and efficiancy. What about these guys that are getting some engine knock with 87 octane?

 

This is nothing new. Computer controlled vehicles have used this system for years. For it to work, the system must first detect a knock. If you truck is going to knock, you'll usually hear it for a short time before the system retards the timing. I'm sure I'm not loosing performance from 87, but those who hear the knock probably are.


From the 04 service manual.

KNOCK SENSOR
DESCRIPTION
The sensors are used only with 3.7L V-6, 4.7L V-8 and 5.7L V-8 engines. On 3.7L V-6 and 4.7L V-8 engines, the 2 knock sensors are bolted into the cylinder block under the intake manifold. On 5.7L V-8 engines, 2 knock sensors are also used. These are bolted into each side of the cylinder block (outside) under the exhaust manifold.
OPERATION
3.7L V-6 / 4.7L V-8 / 5.7L V-8 Engines Only
Two knock sensors are used; one for each cylinder bank. When the knock sensor detects a knock in one of the cylinders on the corresponding bank, it sends an input signal to the Powertrain Control Module (PCM). In response, the PCM retards ignition timing for all cylinders by a scheduled amount. Knock sensors contain a piezoelectric material which constantly vibrates and sends an input voltage (signal) to the PCM while the engine operates. As the intensity of the crystal’s vibration increases, the knock sensor output voltage also increases. The voltage signal produced by the knock sensor increases with the amplitude of vibration. The PCM receives the knock sensor voltage signal as an input. If the signal rises above a predetermined level, the PCM will store that value in memory and retard ignition timing to reduce engine knock. If the knock sensor voltage exceeds a preset value, the PCM retards ignition timing for all cylinders. It is not a selective cylinder retard. The PCM ignores knock sensor input during engine idle conditions. Once the engine speed exceeds a specified value, knock retard is allowed. Knock retard uses its own short term and long term memory program. Long term memory stores previous detonation information in its battery-backed RAM. The maximum authority that long term memory has over timing retard can be calibrated. Short term memory is allowed to retard timing up to a preset amount under all operating conditions (as long as rpm is above the minimum rpm) except at Wide Open Throttle (WOT). The PCM, using short term memory, can respond quickly to retard timing when engine knock is detected. Short term memory is lost any time the ignition key is turned off.

 

That is some cool info. Sure would be nice to be able to easily access the long term memory for graphing purposes and knowing what's been up.

I still wonder about the guys who experience present knowcking. Could it be that the retarding of the spark by the PCM only goes to so many degrees?

 

That's right. It's set to run optimally at 89, but can retard timing several degrees to compensate, and prevent, pre-ignition.

 

Just because an engine computer can decrease timing from the base setting does not mean it can increase timing, too. Most factory computers do not do the latter. In fact, it is doubtful any do; this is an issue of regs, liability, etc. It would depend on the program and system.

Bottom line... more octane than you need is not only a waste of bucks but counter-productive because it takes more to make it burn, all else being equal--that's why it doesn't pre-ignite so easily--it is less combustible, in a sense.

We use the equivalent of 118 octane in our turbo- and supercharged Salt Flats racers, but only because we use a bunch of boost (40# in one car). However, this racing fuel (supplied by the Torco distributor) is no longer sold by octane number but by a different designation. It's also $10/gallon, or was last year. This year it may be $15! We'll see.

 

You all talk about performance and the octane you are using, and while it is true that I bought my Hemi with the performance factor in mind, what is the truth in using too low or too high an octane can damage your fuel injectors over time?

 

This is for Jeff 17. I don't know what book you got this information on Heptane came from, but nobody uses heptane in there Gasoline. I ran an Octane facility for a major gasoline producer on the East Coast for many years.We only used heptane in our test engine's to lower the octane below 80 octane range. Heptane has the same octane rating as water ,Zero. And you know that you can't blend water to any fuels, so they use Heptane. As for 119 octane Lot's of luck on that one. That's a researh test method only. Motor testing can't rate that high an octane. The best ,safest test is 113. on the research Method .R+m-div-by-2= Your outane,That's what it says at every pump in this country. The oil industry uses two test fuels to run a octane sample, 80 oct and 100oct. 80 is made of 20 percent Heptane and 80 percent Issoctane. Issoctane is 100 per pure by it self. Gasoline that we burn in our Auto's has no Heptane in it.