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Jetting in the real world may not be what it says

When you say "pin them",,,,are you measuring the orifice to determine the size?I use drill bits to measure because I don't quite get the number system some of them use.I prefer thousands,,,,
 
HEMI-ITIS said:
When you say "pin them",,,,are you measuring the orifice to determine the size?I use drill bits to measure because I don't quite get the number system some of them use.I prefer thousands,,,,
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Holley Main Jets vs drill sizes #40 - #100.jpg
 
We use these for checking, go no go, gauges at work.
 
I always look at the Holley jet chart which really makes no sense to me when the 91 to 93 jets all have the same .105 drillsize hole in them. They sure look the same to me as I always use my drill sizes when I jet and I dont take out a 91 thats .105 and put 92'or 93's in that are also .105 drill hole size. I will check them and if I am jetting up from 91's that are a .105 size hole I check them and will use a larger hole size jet like a .108 or depending on how much I want to jet up. I found out years ago that Holley jets are not all the size of the number on them which you would think they would be as it would sure make alot more sense. I have all the carb drills I need from .009 to .144 so as I said I always measure the jet sizes when I do any jet changing as I measure whats in the car and I make sure I use a jet of different hole size when jetting up or down. Ron
 
I wonder myself that's why I started this thread. Holley says there rated to the flow after being made. Makes sense to me yet I don't know how you can change the flow on a same size opening and pressure. Maybe a plus or minus factor
 
383man said:
I always look at the Holley jet chart which really makes no sense to me when the 91 to 93 jets all have the same .105 drillsize hole in them. They sure look the same to me as I always use my drill sizes when I jet and I dont take out a 91 thats .105 and put 92'or 93's in that are also .105 drill hole size. I will check them and if I am jetting up from 91's that are a .105 size hole I check them and will use a larger hole size jet like a .108 or depending on how much I want to jet up. I found out years ago that Holley jets are not all the size of the number on them which you would think they would be as it would sure make alot more sense. I have all the carb drills I need from .009 to .144 so as I said I always measure the jet sizes when I do any jet changing as I measure whats in the car and I make sure I use a jet of different hole size when jetting up or down. Ron
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I think you are wrong in your approach. I do believe Holley sizes their jets base on the flow number not the orifice size. I know the orifice size does not exactly determine the actual flow volume at a given pressure drop. If Holley does what they say, they will get a more accurate reading than just measuring the orifice size. I know what I'm saying. I hope they do what they claim. My experience from my old Holley jets seemed to confirm that.
 
66Satellite47 said:
I think you are wrong in your approach. I do believe Holley sizes their jets base on the flow number not the orifice size. I know the orifice size does not exactly determine the actual flow volume at a given pressure drop. If Holley does what they say, they will get a more accurate reading than just measuring the orifice size. I know what I'm saying. I hope they do what they claim. My experience from my old Holley jets seemed to confirm that.
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I'm sure I'm wrong. I started this post to learn and we all got some good information. I'm wrong a lot but I learn from it.
 
Canyon707 said:
I wonder myself that's why I started this thread. Holley says there rated to the flow after being made. Makes sense to me yet I don't know how you can change the flow on a same size opening and pressure. Maybe a plus or minus factor
Click to expand...
the flow changes by changing the angle of the chamfer on the exit side.
 
lewtot184 said:
the flow changes by changing the angle of the chamfer on the exit side.
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That is one of the things that affect actual flow. There are others. That is why actually flowing them makes sense. I hope Holley is still really doing that.
 
66Satellite47 said:
I think you are wrong in your approach. I do believe Holley sizes their jets base on the flow number not the orifice size. I know the orifice size does not exactly determine the actual flow volume at a given pressure drop. If Holley does what they say, they will get a more accurate reading than just measuring the orifice size. I know what I'm saying. I hope they do what they claim. My experience from my old Holley jets seemed to confirm that.
Click to expand...

I have hard time believing Holley's claim. Some jets like the 64 and 65 and many others are the same hole size as the jet number so it makes no sense to me why when they get to certain sizes the jets have the same size hole no matter what they say about the shape and how it flows. I cant see looking at a tiny jet like and intake port flow as the jet is just way to small. Yes they can alter the jet some to maybe give them almost like a venturi effect but they are just to small to make much difference to me. Maybe someone with an 02 sensor setup should try changing their jets to a different number size with the same size hole and see if it does run any richer. It seems that most jets match the number and hole size up to 66. By the number 70 jet it has a hole size of 73. Why would they not still match the number to the hole size after number 66 ?? I know I would still not want to change from 88 jets to 90's when the both have the same hole size of 104 as does the 89 jet. Until I actually know of someone taking 02 readings on the jets of the same hole size but up in number and proving they actually will let the eng run richer I wont change jets to one's of the same hole size. Ron
 
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To me if the flow really changes that much by the jet design then I would think the inlet size would need to be altered as much as the outlet to make sorta a venturi effect. But there is just not that much there to work with in as small as jets are. Ron
 
383man said:
To me if the flow really changes that much by the jet design then I would think the inlet size would need to be altered as much as the outlet to make sorta a venturi effect. But there is just not that much there to work with in as small as jets are. Ron
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Well think what you want. I know what I learned in the big school house, and have seen the math of hydraulics play out in real life. Small stuff works the same as bigger stuff. Believe it or don't. The hole diameter is not the only thing that contributes to flow. Small changes in radius and shape do make a significant effect on flow. Just think about how small the flow is and the pressure drop that creates the flow.
 
66Satellite47 said:
Well think what you want. I know what I learned in the big school house, and have seen the math of hydraulics play out in real life. Small stuff works the same as bigger stuff. Believe it or don't. The hole diameter is not the only thing that contributes to flow. Small changes in radius and shape do make a significant effect on flow. Just think about how small the flow is and the pressure drop that creates the flow.
Click to expand...



I know all about the hole diameter not being the only effect as thats why air flow speeds up in the carbs venturi which is one example. I just have a hard time believing it makes that much difference in the small carb jets. I actually agree with you about a hole diameter is not the only thing to affect flow through it but I just cant see it making much difference in something as small as carb jets. I may be wrong and maybe one of you all can prove me wrong if someone ever does a test on a dyno or on their car with an 02 setup. But until they do when I want to fatten up my car or lean it out I am chaniging to jets with a different hole size. Ron
 
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