How much RPM drop from park to drive with stock type 340 convertor
Mix of terminology...
I knew what the Transfer Slot is but how does the word 'sync' apply ?
Isn't the transfer slot part of the 'off idle' circuit and feed air from the 'air bleeds' ?
I also know with a '4 speed cam' you don't need to drill the primary butterfly... but .. when do you need to drill that 'bleed hole'?
Can only assume it is needed with long duration 'full race' cams.
I'm running a 340, loose convertor, with 484 Hyd Purple (3/4 race ..lol) and a Holley 750 DP 2 port idle adjust ... and don't have or seem to need the drilled butterflies.
So when do you need to drill the butterflies ?
AFAIK 'sync' is AJ's term.
Yes the transfer slot provides most of the fuel in 'off-idle' but also low speed cruise.
As far as being a part of the 'off-idle' circuit yes and no; it's an intergral part of the idle circuit. It shares the fuel in ht eidle down well with the idle port.
Drilling butterflies is what was done when the throttle position at idle is too far open. Drilling allows the throttles to be closed further with the same amount of air as if htey were further open. Holley even supplied some carbs from the factory with holes in throttle plates.
On an old school Holley 4150/60, greater than .040" of transfer slot exposure at slow idle would generally cause problems as the throttle was opened.
The sidebar Urich and Fisher's
Holley Carburetors and Manifolds covers proper throttle to transition slot relationship. (pp. 121-2 in the 1987 edition [Holley Part No. 36-73, HP Books])
The section is called
Special Procedures for Wild Camshafts
I've linked it above but the links to copyright material are often temporary.
Chrysler also explained the carburation circuits in several Master technician's reference booklets. Although the general ones are more oriented toward Carters, there's a lot of overlap with Holleys.
Master Technician Service Conference - Chrysler's Training for Mechanics
Go to the pre-emissions Carburetor Fundementals from 1966 to start with.
The one from 1970 covers a few of the differences on the Holleys along with some of the emissions related changes (such as leaner idle mixture and controls).
Can't the original poster also use a vacuum gauge to see if it drops off too much when dropping it in gear which then disrupts the idle fuel/air mixture. ?
Yes. especially if using a tach thats hard to read rpm drops finer than 250 or 200.