changing q-jet secondary rods

[Xbody]

Originally Posted by Mark Yacavone

I'd say 5-6 thou, depending on what's available..
If you're still foot braking, you might see a change with the hanger too.
Try to stay in the median alphabet range
It your carb won't run that way, there's always the seat of the pants method..Almost lost in this day and age.

Mark,please define median alphabet range

thanks john

[Mark Yacavone]

Originally Posted by Xbody

Mark,please define median alphabet range

thanks john

Hangers are lettered A-V I think. Each letter down the alphabet will pull the sec. rod out of the jet .005 later.
Starting with say a K, L M will give you room to fine tune in either direction.

[Dave1695]

Had 57s on a J in it last night, switched to 55s on the same J, no difference. Don't have too many rod sizes, just put 44s on the J for next week. Have an H and I that could go in too.

[Mike Pearson]

Originally Posted by Dave1695

Had 57s on a J in it last night, switched to 55s on the same J, no difference. Don't have too many rod sizes, just put 44s on the J for next week. Have an H and I that could go in too.

My car is a super stock car. I never run anything smaller than a .057 rod. In the heat I usually run .066 rods. J or K hanger. That’s what I had in at Atlanta last weekend and it picked up from the .057 that I had in for the first Q pass.

[Dissident]

Easiest thing to do is calculate the square inches of area of the main secondary jet which is fixed (I use 0.135" diam = Area of 0.014313915 sq in) then subtract the area of the secondary metering rod tip so the difference is the functional area of the secondary jet with that metering rod. As an example, the guy that raced his SS in Atlanta said he used a 0.057" and a 0.066" tipped rod so that is a change of area of 30%.....wow. Normally one would want to change only about 5% or so at a time, but that is just a suggestion. Whatever works for you.
Best thing to do is to make a chart or table of whatever your metering rod tip selection is and do the arithmetic.
Regards to all that like this kind of stuff.
Otherwise just put your mask on and change the channel to reruns.
HB2
Dissident

[James Perrone]

You want to see a difference ?
Go from a 55. To a thin 34 Rod.
It’s basic tuning. Throw a bunch of fuel. See what happens
It’s probably too much but then try something in between
It’s seat of the pants Tuning it works for me.
Hangers. Same thing B hanger is most aggressive. Then D. E. F
You won’t know unless you try

[Stan Weiss]

Can someone post up what the weather is when they run a 0.057" rod and when they run a 0.066" rod? Looking to see how far off my math is.


Stan

[Stan Weiss]

Originally Posted by Dissident

Easiest thing to do is calculate the square inches of area of the main secondary jet which is fixed (I use 0.135" diam = Area of 0.014313915 sq in) then subtract the area of the secondary metering rod tip so the difference is the functional area of the secondary jet with that metering rod. As an example, the guy that raced his SS in Atlanta said he used a 0.057" and a 0.066" tipped rod so that is a change of area of 30%.....wow. Normally one would want to change only about 5% or so at a time, but that is just a suggestion. Whatever works for you.
Best thing to do is to make a chart or table of whatever your metering rod tip selection is and do the arithmetic.
Regards to all that like this kind of stuff.
Otherwise just put your mask on and change the channel to reruns.
HB2
Dissident

Yes a large change in metering rod area but a much small % change in total flow area.


► ((.057/2)^2*pi)/((.066/2)^2*pi) = 0.7458678
► ((.066/2)^2*pi)/((.057/2)^2*pi) = 1.34072022



Stan

[GTX JOHN]

Originally Posted by Stan Weiss

Yes a large change in metering rod area but a much small % change in total flow area.


► ((.057/2)^2*pi)/((.066/2)^2*pi) = 0.7458678
► ((.066/2)^2*pi)/((.057/2)^2*pi) = 1.34072022



Stan

You lost me on this one = If the metering rod is inside the jet and
displaces a segment of the jet area does it not proportionately
restrict the volume or Air Flow?

Sorry I am OLD and not particularly sharp anymore!

[Mike Pearson]

Originally Posted by Dissident

Easiest thing to do is calculate the square inches of area of the main secondary jet which is fixed (I use 0.135" diam = Area of 0.014313915 sq in) then subtract the area of the secondary metering rod tip so the difference is the functional area of the secondary jet with that metering rod. As an example, the guy that raced his SS in Atlanta said he used a 0.057" and a 0.066" tipped rod so that is a change of area of 30%.....wow. Normally one would want to change only about 5% or so at a time, but that is just a suggestion. Whatever works for you.
Best thing to do is to make a chart or table of whatever your metering rod tip selection is and do the arithmetic.
Regards to all that like this kind of stuff.
Otherwise just put your mask on and change the channel to reruns.
HB2
Dissident

I have been racing my car for many years so I know what it likes in certain air conditions and I set the carb according to that. I run the .066 rod when it is hot and humid. In Atlanta it was almost 90 degrees and the humidity was near 80% most of the weekend DA about 3500 ft. The first couple of passes I still had the cold weather set up in the carb. That was the .057 rods. I had that in from the Baby Gators just before the shut down. The DA there was below 1000 ft and the humidity was about 30%. I don't know anyone that runs rods richer than a .057 unless you are trying to air leak the carb. Personally I have never tried that. I have 2 good Q jets that were built by well known builders. They both respond the same to similar changes. My car always runs best on the lean side.