Can excessive lifter preload cause bad idle?
Just looking for a little feedback: I have gotten my engine to idle pretty good with idle circuit mods per Cliff Ruggles, but I think it could be better. Initial timing is 22*, total timing is 35* all in before 3000 rpm, vacuum advance is 10*. Idles at 800 rpm in park and 600 rpm is drive with a bit of a lope, with 14" hg and 10" hg vacuum respectively @ 4000 feet above sea level. Cam is TA 212 and degreed in at 109* ICL. Is this about what kind of vacuum to expect at idle with this cam? Is my timing about in the ball park? If the initial timing is backed off, vacuum will fall off and the engine will not idle at all, in fact it will just plain die below 1000 rpm. I suspected a vacuum leak so I replaced the Edelbrock composite gasket and trimmed down steel valley pan gasket per TA instructions, with just a new steel valley pan gasket with 3 coats of copper coat (the composite gasket was sliced at the bottom from the edge of the valley pan and was actually being squeezed out the top by about 1/8"). There was no change. When I built the motor, the exhaust valves were replaced with 1.755" TA stainless steel valves, but the factory intake valves were reused. As a result, the intake valve stems are about .020" higher than the exhausts. The heads were milled to clean up (.010"? and I don't know if they have been milled previously) and the block was decked about .010". The pushrods are stock length with stock rockers. I didn't measure the exact lifter preload, but the lifter plungers were about 1/3 of the way down their travel on the exhausts, while the intakes were down about 2/3's. Not ideal, I know. I am wondering if this excessive preload could be preventing the engine from idling at it's best? Is 22* initial timing too much to run with this mild of a cam? I would like to run 10*-12* initial, or am I just worrying about nothing? Would like to know before I spring for shorter or adjustable pushrods, or do the right thing and take the motor apart and have the intake valve stems cut down .020"--would any of these improve anything? Thanks for reading this far.
Steve, Rapid City, SD
1969 Chevrolet C/10: 1976 455 BBB, stock block, .030" over KB 357 pistons, .000" deck height, 9.75:1 CR, stock rods w/arp bolts, stock crank .010"-.010", TA oil pump booster plate and adj. regulator, TA 212 cam, stock valve train, 1972 pocket ported Stage 1 heads, B4B intake, 800 cfm Q-Jet, ported exhaust manifolds, 2 1/2" exhaust, Flowmaster Deltaflow 50 mufflers, TH400, stock converter, 3.73 posi truck 12 bolt, 3800 lbs empty.