i have a 347 and i want to make sure my engine is running right but when i but my wide span vacuum gauge on it at idle the vacuum is very low but it goes to a very good level once reved, now i have a faily big cam in the car would that cause the low vacuum at idle????
To expand a bit that's why you will hear the term a "streetable" cam. This is one that will give you a smoother idle and produce enough vacuum at idle to power things such as power brakes etc.
You can and should adjust your idle micture on the carb for max vacuum at idle as well. You might pick up a little between this and timing. Base timing should be between 12-16 degrees (my 347 likes about 16).
i have a 347 and i want to make sure my engine is running right but when i but my wide span vacuum gauge on it at idle the vacuum is very low but it goes to a very good level once reved, now i have a faily big cam in the car would that cause the low vacuum at idle????
You bet. Now, if you want to smooth out the idle, and get better vacuum (which is real important if you have power brakes) use a set of Rhoads lifters. They have a groove in the inner piston that allows the lifter to reduce lift and dwell at low rpm. I have been able to get a 400 rpm idle out of performance cams using them.
My vacuum is right at 12 inches and my power brakes work fine. You might be right on the bubble, but if you can get it to maintain 12, you would be fine with PB.
My vacuum is right at 12 inches and my power brakes work fine. You might be right on the bubble, but if you can get it to maintain 12, you would be fine with PB.