David Vizard":2633gout said:
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Carb Boosters
- Thread starter Pinhead
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Pinhead, booster designs can make large carb seem small.
I had a 4412-500 carb i sent to holley & had the stock down leg boosters replaced with annular discharge boosters.
The part throttle & general drivability of the carb was much improved, however since the venturi diameter was not bored out, the full throttle performance did not match the performance of the stock boosters on the 4412.
Hence since the annular boosters improved the signal but the lack of total CFM air flow caused a loss of top end power compared to the stock downleg boosters.
The main jet went from 69 on the downleg boosters to 63 on the annular discharge boosters.
All the air fuel ratios were optimized using an innovate wideband air fuel ratio tester.
If i had to do it over again i would bore out the main venturi to regain the air flow lost from the more restrictive annular discharge nozzle.
This carb would be perfect on a mild mod engine, the performance is between the 7448-350 & the 4412-500.
For what its worth, Bill
I had a 4412-500 carb i sent to holley & had the stock down leg boosters replaced with annular discharge boosters.
The part throttle & general drivability of the carb was much improved, however since the venturi diameter was not bored out, the full throttle performance did not match the performance of the stock boosters on the 4412.
Hence since the annular boosters improved the signal but the lack of total CFM air flow caused a loss of top end power compared to the stock downleg boosters.
The main jet went from 69 on the downleg boosters to 63 on the annular discharge boosters.
All the air fuel ratios were optimized using an innovate wideband air fuel ratio tester.
If i had to do it over again i would bore out the main venturi to regain the air flow lost from the more restrictive annular discharge nozzle.
This carb would be perfect on a mild mod engine, the performance is between the 7448-350 & the 4412-500.
For what its worth, Bill
Since when did amplifiers start getting called boosters?
Of course the carb can be too big, or at least the throttle/choke plates can be. There's a basic control function called throttling range that needs to be accounted for, which usually means the plates have authority over the flow, not the inlet tract and intake valves.
Of course the carb can be too big, or at least the throttle/choke plates can be. There's a basic control function called throttling range that needs to be accounted for, which usually means the plates have authority over the flow, not the inlet tract and intake valves.
Well done
Yes, IF adjusted properly a big 4v will work on a small engine...IF. Even in stock form our engines will probably have no problem of handling the 400 cfm primaries of a 800 cfm carb at the rated 1.5hg. The problem comes when expecting our engines to handle 800 cfm. That is why the secondaries must be adjusted so the engine determines...based on flow...when it can handle more cfm and IF this adjustment is correct the engine may never actually draw the full 800 cfm. That same principle applies to AFB/Edelbrock, Qjet and Holley carbs...it's all in the adjustment of when and how much the secondaries open. Holley Tech Service advised me that my 450 cfm spread bore flows 200 cfm through the primaries. That leaves a 250 potential cfm in the secondaries (mechanical...not much adjustment there) and if I go WOT aggresively at too slow a speed I can get hesitation or even bog until there is enough flow/signal in the carb to draw fuel through the secondaries. When I am less aggressive going WOT allowing a stronger signal to build it goes like a raped ape as vacuum rises which brings up another point. When vacuum rises above the rated 1.5hg the carb is no longer flowing at the rated cfm but is flowing less. On the other hand, if vacuum is less than 1.5hg say 0.5hg the carb may be flowing more than it's rated cfm. Correct A/F ratio throughout all this must be maintained.
An interesting study is Holley's charts on "Numerical Listing And Component Parts" where carbs with 1 9/16 throttle bores and 1 11/16 throttle bores can both be rated at 600 cfm the difference being in the venturi diameters and boosters. Main jets may be any where from 62's to 69's. Secondary jets/metering plates are just as varied...Tons of variables and combinations.
And thanks for the OZ English/American English Thesaurus
.
An interesting study is Holley's charts on "Numerical Listing And Component Parts" where carbs with 1 9/16 throttle bores and 1 11/16 throttle bores can both be rated at 600 cfm the difference being in the venturi diameters and boosters. Main jets may be any where from 62's to 69's. Secondary jets/metering plates are just as varied...Tons of variables and combinations.
And thanks for the OZ English/American English Thesaurus
.
There are five boosters Holley uses for its 2300/4150/4160/4165/4175/ 4360 and 4500 carbs, not all interchange.
The annular discharge ones are very good at creating signal, and if all is gasflowed to the carb, they should give no major cfm drop than the worst of the Economaster and Truck style boosters (as used on the rare 1976 350 cfm Holleys which were actually 320 cfm, and the IH Truck Holleys). These drop cfm at 1.5"Hg by 35 cfm on a 750 Holley, and 30 cfm at 3.0"Hg on a 350 cfm Holley.
The stock booster is as good as the best item. When used in independent runner set-ups, 4500 series carbs use long boosters which allow fuel standoff to be contained. These flow brilliantly, but are not transferable to 2300/4150 carbs, and are too sensitive for a stock single carb I6 or V8 application where the carb is under very high vacuum. 3.0"Hg is a realistic wide open throttle pressure drop for an I6 with a 350 cfm 2300 series carb.
Its all a delicate balancing act. The key is creating the right adjustable mixture without loss of wide open throttle CFM.
The annular discharge ones are very good at creating signal, and if all is gasflowed to the carb, they should give no major cfm drop than the worst of the Economaster and Truck style boosters (as used on the rare 1976 350 cfm Holleys which were actually 320 cfm, and the IH Truck Holleys). These drop cfm at 1.5"Hg by 35 cfm on a 750 Holley, and 30 cfm at 3.0"Hg on a 350 cfm Holley.
The stock booster is as good as the best item. When used in independent runner set-ups, 4500 series carbs use long boosters which allow fuel standoff to be contained. These flow brilliantly, but are not transferable to 2300/4150 carbs, and are too sensitive for a stock single carb I6 or V8 application where the carb is under very high vacuum. 3.0"Hg is a realistic wide open throttle pressure drop for an I6 with a 350 cfm 2300 series carb.
Its all a delicate balancing act. The key is creating the right adjustable mixture without loss of wide open throttle CFM.
