I posted a reply to a question in the street section about Idle Feed Restriction Location in that thread.
I will post my comments in the Holley section here so that the info is in a common location vs lost in the other thread.
Formula jg post #77:
"I know you like the way it’s running now and that you will be away for some time so I just want to share
my experience with tuning several carbs that had the IFR located in the upper section of metering block. Once i relocated them to the old school Holley position (bottom of the metering block) it made the carb much, much more responsive. It also made it easier to tune out any flat areas or hesitations.
The difference in location of IFR was explained to me several years ago and it made total sense but I can’t explain it properly today, however I’m sure another member here could."
My Reply Posts: (Post #78
The best location for the IFR (Idle Feed Restriction) was identified in carburetors and the results reported in NACA REPORT #49 (Part II on page 607) See link below.
http://naca.central.cranfield.ac.uk/...-report-49.pdf
In the conclusions part of the document, conclusion #4 clearly states that:
"Submerged Fuel Metering Passages (IFRs) are free from Instability and Irregularity of discharge when the head is very small."
You can not have a submerged Fuel Metering Passage when the IFR is in the "HIGH" Position, (only the "LOW Position").
There are 10 other conclusions and all of them are correct.
Many Carb Tuners have converted back to the Low Position IFRs even though the Holley Carb came stock with the High Position IFRs.
Hope this helps.
The Report #49 is available on the web and is well worth reading if you really want to understand carburetors.
Tom V.
Formula jg post #79:
I knew it could be better said than ever could, thank you Tom.
My Reply Post: (Post #80)
No problem, thanks for the reminder that the info is out there once you know where to find it. But without some incentive to post it, I tend to just state the conclusion and not where the knowledge came from. Some believe that because a company is a Carb Company they actually know something about carbs.
Many Years Ago, (mid 1970s), Holley Engineering had employees buy modified Holley carbs from over 25 modifiers. (I have posted this info in the past).
This way the Modifiers did not know the carbs would be taken apart by Holley Engineering and each modification analysed.
Of the 25+ Modified carbs, only 3 carbs actually were slightly better vs the stock out of the box Holley carb and the HP difference was never more than a couple of HP. Lots of cash spent and no real bang for your buck.
A lot of this deal is "Monkey see, Monkey do" vs actually having read data generated by some of the smartest people in the world who wrote the NACA papers on Carburetors like the Paper Report #49 mentioned above.
Look at any Rochester 2-BBL carb. Where is the Idle Feed Restriction? At the bottom of the Idle Tube in the cluster assy. Guess why it is there. Liquid Fuel (A Submerged Fuel Metering location). Same deal for a Carter AFB.
Easy to drill a hole in a different part of a fuel circuit and claim that it is a better location. "Send me the money for my "modified Holley carb".
Tom V.
So now the info is saved to this thread.
Tom V.