Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Which Recipe Best For My Setup?
old cars:
You can calculate the LSA using the centerlines of the intake and exhaust lobes.
Intake Centerline + Exhaust Centerline - divide by 2.
106 + 114 divide by 2 = 110 LSA
"Valve lift is 0.470" Intake and 0.480" Exhaust using 1.6 ratio pushrods"
I assume you meant rocker ratio. Stock rocker ratio is 1.5
"I am trying to figure out what I would have for manifold vacuum at idle. I am thinking 12-15 psi but not sure."
110LSA / I would think between 12 and 14 in/vacuum
Cliff Ruggles:
It's difficult to predict vacuum at idle as there are a lot of things that effect those numbers beyond the camshaft choice.
The true static compression ratio is a big player there, as is where the initial timing is set at idle speed.
I'm not a big fan of adding a butt-ton of timing at idle and consider having to do so to offset the negatives of a poor cam choice more of a "crutch" than anything else.
Carburetor tuning will also have an impact on vacuum production, especially with larger camshafts that lower the signal to the carb at idle speed. Simply bringing in adequate fuel to the mixture screws does wonders for idle quality and vacuum production with many of these engine combo's........Cliff
old cars:
Going to need idle bypass air?
Tinkerman:
--- Quote from: old cars on August 27, 2021, 03:59:46 AM ---Going to need idle bypass air?
--- End quote ---
Idle bypass air is at 0.075". That is probably borderline but should be enough.
Cliff Ruggles:
Yes, with 110 LSA I'd start out with about .090", fine tune, and see if you have good sensitivity from the mixture screws w/o nozzle drip. At that point there are several tests that can be done to decide which way to move forward if it still needs a little help.....
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