Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
idle help
lightning boy:
What is the compression height of the piston and what is the head gasket thickness?
Did you perform the compression test with the throttle all the way open and all the plugs removed?
Seems low.
Put a mighty vac on the brake booster and see if it holds. Trans vac line too.
How did the valve springs look on the #2 hole?
73ss:
--- Quote from: lightning boy on December 17, 2021, 07:59:04 AM ---What is the compression height of the piston and what is the head gasket thickness? Machinist said pistons are 10 in the hole. I measured around .008", Hard for me to get a good measurement due to dome and piston rock at TDC. Head gasket is cometic, .040 thick.
Did you perform the compression test with the throttle all the way open and all the plugs removed?
Seems low. Yes
Put a mighty vac on the brake booster and see if it holds. Trans vac line too. Brake booster good, OD trans no vac line.
How did the valve springs look on the #2 hole? Springs & valves are great, Not sticking, Valves seal excellent on that hole. Rocker geometry is good.
--- End quote ---
I think this cam has too much overlap, card says 63.6 * overlap for advertised and 11.6* overlap at .050 lift.
Cliff Ruggles:
What is the advertised duration and check point?
The cam in my 455 is 289/308 @ .006" tappet lift, 112LSA and ICL at 109.5 and it makes 13.5" vacuum at 750rpms with only 10 degrees timing in it. Cranking pressure is 198-200psi across the board..
230/246 @ .050" is not a big cam in that engine and with 114LSA it shouldn't have a lot of overlap.
Late intake closing lowers cranking compression and will make the engine somewhat "lazy". Even with that said that little cam in a near 500CID engine with 10 to 1 compression it should me idling with a LOT more vacuum and not having to run more than 10-12 degrees initial timing.
Something is fundamentally wrong someplace......IMHO......
73ss:
I agree with your comments, Thanks for the tips. Some of the poor vacuum should be due to the #5 intake not sealing well. I don't see anywhere on the card at what lift they take the advertised duration at.
tayto:
"Degrees of Duration" 284.6*/289.6*
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