October 11, 2018, 09:46 PM
EmanCarburetor jet question
I guess that will work, I've got the Moroso style that fits around the jet and in the slot.
November 05, 2018, 05:42 PM
EmanHolley got back to me, I asked about the differences in the jets they sell, they list Holley,QFT and Demon jets. They said they are all the same some people just want to buy them under certain brands. Makes you wonder.
https://www.holley.com/product...ds_bleeds/main_jets/ #78 jets and the Holley says .089 and the Demon and QFT say .078.
November 06, 2018, 09:22 AM
TOP38[QUOTE]Originally posted by nomad:
Holley jets are rated by flow. The flow is determined by the length of the orifice and the diameter of that orifice (L/D ratio). While two different numbered jets can have the same orifice diameter the length can be different. Thus different flow amounts. A chamfer on the leading and trailing edge of the orifice alters flow also. This was all worked out in 1919 by NASA, then NACA. in TR-49 available on line.
QUOTE]
The diameter and length of the jet hole do matter however the entry and exit shapes matter MUCH MORE that either of the above two with regards to flow quantity. This why the injection folks instruct you not to stick a pointed tip in the bypass pills to pull it out as you could alter the entry shape or exit shapes! A small chamber added to sharp edge can make a world of difference!
This is why it's recommended to go at least two jet sizes when making a change as you could be thinking your richening the motor when in fact your leaning it! Also it pays off big time here to have a data logger with O2 readings to confirm what you want to do vs what you really did!
November 07, 2018, 06:48 PM
jmarkaudioquote:
Originally posted by TOP38:
[QUOTE]Originally posted by nomad:
Holley jets are rated by flow. The flow is determined by the length of the orifice and the diameter of that orifice (L/D ratio). While two different numbered jets can have the same orifice diameter the length can be different. Thus different flow amounts. A chamfer on the leading and trailing edge of the orifice alters flow also. This was all worked out in 1919 by NASA, then NACA. in TR-49 available on line.
QUOTE]
The diameter and length of the jet hole do matter however the entry and exit shapes matter MUCH MORE that either of the above two with regards to flow quantity. This why the injection folks instruct you not to stick a pointed tip in the bypass pills to pull it out as you could alter the entry shape or exit shapes! A small chamber added to sharp edge can make a world of difference!
This is why it's recommended to go at least two jet sizes when making a change as you could be thinking your richening the motor when in fact your leaning it! Also it pays off big time here to have a data logger with O2 readings to confirm what you want to do vs what you really did!
That is why I use BLP jets in all new builds, most reworks unless it's a simple rebuild. Jets come in .001 increments, and are not sensitive to irregularities if you have to ream them because they are deigned with a chamfer. With anything that is sharp edge the slightest chamfer or nick in the edge will alter the flow significantly, if it starts off chamfered the size of the chamfer has only a small impact.
