Jetting area calculator

Well,

I've finally got the truck back running after the fire (work-related drama taking up my time)...

Went for another cruise; seems like it's too lean off-idle. Have .073/.047 metering rods in it.

Have decided to go thru my stash o' rods and maybe change jets, too.

But, being one of those 'semi-educated' types, I decided to actually 'mathematic' out the areas. Then, I decided to put my newly acquired excel skills to use, and make a spreadsheet so I don't need to break out the calculator every time.

And then I thought, "gee, I should post the spreadsheet on moparts, so others won't have to break out the calculator".

So, here it is (download the attached .xls file)...

You can enter up to four steps of metering rod size. Helpful if you want to a) calculate a 3 step rod, or b) calculate TWO different metering rods.

I have already entered values for a .070X.037 and a .062X.045 rod and ..098 and .104 jets. These are the values you change for your application - they're green and bold; the areas of the jets minus the area of the metering rod is found in the 'effective area' column.

Hope this helps someone else, and enjoy!

-Bill

ain't tuning fun Good job on the help

Hey Cab, I think tuning is fun.

But then again, Lulubelle seems like she's going to be needing a bunch of that fun.

I get the feeling that the engine isn't really making all the power it should - yet.

If I can dodge (pun intended) the rain showers, I'll have to see if there's an oddball jet or rod in the rear carb pass side primary; the #6 & 8 plugs looked nice (light tan), while all others were very pale. Maybe that's just an idiosyncracy of the M1 tunnel ram.

-Bill

Update: I got the truck into the carport... staying relatively dry. And, I realized that the description of what the spreadsheet does and how to use it might not really be detailed enough to help everybody.

So, I'll do a little 'show and tell'...

Since I just ran her for ~60 sec to pull her in, the plugs are pretty wet and hard to read.

Heat range is probably okay; a couple threads show some color.

So I've read on the internet...

I didn't check 'em all, since they were wet, but it looked like #6 was a little darker than #5. I'll re-check after running up to fully warm. But, they seem to match the last set of plugs I had in her.

All 4 primary barrels have .104 jets and .075X.047 rods; this gives an effective area of .0041 and .0068 square inches at cruise and power settings. Since almost all the driving I've done is at less than 1/4 throttle (all on the street, ys' know), I'm not sure I even get into the power portion of the metering rod often and long enough to color the plugs at all.

I'm going to change to .101 jets and .068X.042 rods, which will give me effective areas of .0044 and .0066 in/sq. So, about 7% richer at cruise, and about 3% leaner at power settings.

If the screen capture of the chart shows up, it'll show how I came up w/ this.

Now to try it out.

If anybody has any ???'s about how to use this, or needs any kinda' help, just shoot me a PM.

-Bill