Gonna get to my injectors and ip finally!!

[bbjordan]

Specific Gravity and Cetane value

FWIW, the chart is incorrect. Higher Cetane fuel requires less advanced timing than lower Cetane fuel. So, either it should be BTDC instead of ATDC, or the numbers are in the wrong order.

http://en.wikipedia.org/wiki/Cetane_number

As for measuring the cetane value, from the Haynes Diesel Engine Repair Manual:

"Cetane value is determined by measuring the specific gravity (density) of the fuel with the fuel temperature between 75 and 95-degrees F."

The specific gravity is measured with a hydometer. Again, from the Haynes Diesel Engine Repair Manual:

Hydrometer Reading Cetane Value
.837 .......................... 50
.846 .......................... 47
.849 .......................... 46
.858 .......................... 43
.862 .......................... 42
.876 .......................... 38

You could also weigh the fuel to determine the specific gravity. Take 1000 ml (1 Liter) and weigh it. If it weighs 858 grams, the cetane value would 43.

* Users of the Imperial system of measurement are in for a whole lot more math. I love the metric system.

That being said, I don't know of anyone that measures the specific gravity of fuel except for racers. That is why it is best to have your own tools to do your own timing. That way you can time your engine for the type of fuel you are running.
With a little bit of trial and error, and some record keeping, you can have your engine running at its true potential.

 

[FORDF250HDXLT]

FWIW, the chart is incorrect. Higher Cetane fuel requires less advanced timing than lower Cetane fuel. So, either it should be BTDC instead of ATDC, or the numbers are in the wrong order.

the chart is correct.your correct as well.the higher the cetane,the less advance you need.however when timing via lumy,it's done at ATDC and the higher number values = retarded and lower values = advance.
so when your adjusting timing,and as you move towards 1 ATDC timing would be overly advanced with 10 being overly retarded.

when most of us time via the pulse method today at 2k rpm,our timing lights show the lower number means more retarded with the higher numbers meaning more advanced when timing BTDC.

 

[bbjordan]

I stand by what I say. The chart is incorrect. Look at the chart again.
Why would a high cetane fuel of 47-50 require more advance 4* ATDC compared to a lower cetane fuel of 38-42 at 6* ATDC?
The chart goes against logic and makes no sense.

When I first looked at this chart years ago, I was scratching my head over it. I've scratched so much, I only have about half my hair left. I finally came to the conclusion that the info in the manual was incorrect. It wouldn't be the first time. Probably won't be the last either.

 

[bbjordan]

Sorry to have killed your thread Gavin. I'm not trying to cause trouble.

But seriously, get your engine pulse timed to 9.7* BTDC (that seems to be the best number the collective has come up with, and I concur). I think you will be very pleased with both the performance and mileage.

I would offer more info regarding the relationship between pulse timing and luminosity timing, but unfortunately my timing light only goes down to 0 then jumps to 90. So, I need some timing tape to do this. That, and I'm just too damn busy to do it.

 

[gdhillon]

No no your not starting any trouble, i appreciate you guys taking time out of your days to give me info. Now I am all excited, ill make it my mission to find someone in town with a pulse meter that can time it to where i want