Interesting Math

E

EPA Violator

CR Wrencher
Joined
Mar 8, 2008
Messages
560
Been doin' some figurin' It turns out that with 03-04 injectors, 143 deg spray pattern you actually spray outside the bowl at about 12 deg or so before TDC. I am sure Smarty and all the others advance the timing more than this even with the mild timing settings. This kinda dispells the hypothesis that timing advance is melting these things, because if that was true we all would have melted pistons.

Found something else out, 1 deg equals about .026 in., so worrying about pulling the injector up too much with thicker gaskets and spraying out of the bowl is unfounded. With .052 thicker gasket you only artificially advance the timing be 2 deg. Well, back to the calculator. Jay
 
Gonna measure an 04.5 bowl and figure it up, but looks like it will stay in the bowl till about 16-18 deg. All of these figures are assuming the injector tip it at the piston at TDC, it is actually up some, haven't measured that yet.
 
Forrest Nearing said:
at what RPM? :confused:
Click to expand...

I don't know much about this at all but spraying on the edge of the bowl with stock timing?

I guess it makes cents making the most as far as spray pattern goes on cummins part.

But that would mean that any advanced timing even say smarty TNT on 4 would be outside bowl then right?

Again I am a rook as far as this kinda talk goes.
 
shouldnt matter what RPM, a degree is still one degree...
 
^^^^True but don't C rail's have dynamic timing and with rail pressure added in wouldn't that effect things?

again i'm a c rail rook please explain.
 
why do you aim farther ahead of an animal the faster it's traveling?

could it be because it's not going to be in the same place when you pull the trigger as it's going to be when the bullet arrives?
 
dang like birds that must be my problem.

But seriously can i get a charles type explanation on this one?:hehe: know what I am saying?

I find it odd that anything over 12 degrees is outside the bowl.
 
EPA Violator said:
Been doin' some figurin' It turns out that with 03-04 injectors, 143 deg spray pattern you actually spray outside the bowl at about 12 deg or so before TDC. I am sure Smarty and all the others advance the timing more than this even with the mild timing settings. This kinda dispells the hypothesis that timing advance is melting these things, because if that was true we all would have melted pistons.

Found something else out, 1 deg equals about .026 in., so worrying about pulling the injector up too much with thicker gaskets and spraying out of the bowl is unfounded. With .052 thicker gasket you only artificially advance the timing be 2 deg. Well, back to the calculator. Jay
Click to expand...

You can not divide 4.72 stroke by 180 degrees to get .026=1 degree, it does not work that way.Injector angle is combined angle not 143 deg each way.You can go alot more than 12 degrees and still be in the bowl.
 
What combined angle? If you take half of the 143 to make a right triangle, one side of the triangle is radius of the piston top, one side distance from injector tip to piston top and the other the hypotenuse. use tangent 71.5 and 0.55 in. radius of bowl give distance from injector tip to piston top.

How is .026 in not 1 deg. You do agree there are 180 degrees in the travel of a piston either up or down once, right? Stroke is 4.720 in., right?
 
Your math assumes direct linear motion, but crank throws rotate around the mains' axis - thus piston speed (and therefore thousandths/degree) is much higher mid-stroke than while approaching TDC.
 
XLR8R said:
Your math assumes direct linear motion, but crank throws rotate around the mains' axis - thus piston speed (and therefore thousandths/degree) is much higher mid-stroke than while approaching TDC.
Click to expand...

Just what I was going to say...He is assuming the crank travel is fully vertical and is leaving out the rotational effect completely. IIRC my 12 valve engine has around 4 or 5 degrees "dwell time" within a few thousandths of TDC. Even though it's a 12 valve the rotational crank motion has the exact same effect on any internal combustion motor. Common rail included :Cheer:

Roughly looks like this...
untitled-1.jpg
 
EPA Violator said:
Been doin' some figurin' It turns out that with 03-04 injectors, 143 deg spray pattern you actually spray outside the bowl at about 12 deg or so before TDC. I am sure Smarty and all the others advance the timing more than this even with the mild timing settings. This kinda dispells the hypothesis that timing advance is melting these things, because if that was true we all would have melted pistons.

Found something else out, 1 deg equals about .026 in., so worrying about pulling the injector up too much with thicker gaskets and spraying out of the bowl is unfounded. With .052 thicker gasket you only artificially advance the timing be 2 deg. Well, back to the calculator. Jay
Click to expand...

Even though the 555 motor's bowl design helps them reliably withstand additional fuel timing compared to 600 series, the main problem - thermally speaking - is the aluminum alloy's increased heat soaking during a longer, larger combustion event(s).
Add RPM to the equation (powerband usually goes up with HP), and the pistons' effective cooling window is shortened - which further promotes excessive crown temps.

Also, thicker head gaskets or injector washers don't advance timing - but they can force timing retard, since placing the injector tip further away from the bowl allows fuel to impinge the crown/ cylinder wall at lower total timing.

To accurately model the effect of injector position on the combustion event, you have to consider the relative location of the tip & bowl at SOI.

We build to drop the injector down the bore - allows more fuel timing before bowl containment is compromised. :Cheer:
 
OK, thanks guys. But, the calculation of the injector spray angle is right, correct? Has anyone looked at how early you can start spraying without being outside of the bowl on the 03 and late model CR's? I know the timing is dynamic but I am just referring to the max limit.
 
Just found the formula for piston travel vs. crank rotation. gonna see what that comes up with.
 
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