I have a 69 l78 chevelle rebuilt by local machine shop. He used a bullet cam (int 244/ exh 248 at .050 duration). Gross valve lift (int .592/ exh .588). Lobe separation 110. My power disc brakes work sometimes and then they don't. If I set the idle up to 1200 I get more brakes. I think the cam is too big for a restored original car. I gave my engine guy the stock specs for the L78 and wanted something a little more than stock. Is there any way to get more vacuum without changing the cam? I have everything stock (4346 holley and exhaust manifolds) and don't want to put a vacuum canister on the car.

How much vacuum do you have?
My 355 only has 8" of vacuum, and I have no problems with the power brakes....
Put a vacuum gauge on it,(manifold vacuum source) engine warmed up, (in gear if auto) and set the air/fuel mixture on your carb until you see the highest reading. Both screws should be about the same. 1 1/2 turns out is a good place to start.
Clamp the vacuum connection(s) as well to prevent leakage. Check for other vacuum leaks.

Gleek,

Two things on this. First, if you have a slow ramp cam with real long traditional seating values, you will have a lot of overlap and the resulting low vacuum at idle. Second, the original BBC solid cam with similiar .050 duration was ground on 114LSA, a 110LSA will be much less prone to civil street manners than the 114LSA grind.