Join Date: Aug 2001
Location: Lawrenceville, PA, USA
What should the ported vacuum typical be at idle?
I have a gauge I put in the dash to replace my clock. The line is "T-ed" into the distributor vacuum can line that connects to the front of my Holley 650, dual feed with Vac. Secondaries.
The gauge reads about 7" at idle @1000rpms.
As I open the throttle the vacuum climbs to about 15".
Driving I have seen it as high as 18". Does this sound about right?
I am getting ready to recurve my HEI and wondering if I can use the vacuum can. I have read that with a radical cam you shouldn't use the vacuum advance because to idle the initial timing will already be set to about 18*. (I think I am at 14* now and it doesn't like to idle below 900rpms). Plus, if the vacuum rises off idle with a radical cam you wouldn't want it pulling more advance into the mechanical curve.
What signifies a radical cam?
If I unhook the vacuum can will I suffer gas milage or other performance problems?
Would switching to manifold vacuum be better? (I don't want to start a debate on ported vs manifold, just looking for suggestions.)
The car is mainly a street car, I will probably race it a few times once I get it broken in but more of a toy to cruise in and have fun. So I am looking for a curve and setup that will give performance but keep the motor safe from detonation.
'79 Z28, 4spd, 3.73 10 bolt, 350 4-bolt .030 over with stud kit, 10:1 Compression, Keith Black Flat Tops, Comp Cams Magnum 294 Solid Cam .525 lift, 63cc Heads, Stainless valves, hardened exhaust seats, guideplates, Summit Needle Bearing Roller Rockers 1.5 ratio, Offy Single Plane Intake, Holley 650 Vac. Secondaries, Stock HEI (for now), Headers 1 7/8" primaries, 3" Collectors into 2 1/2" exhaust with "H" pipe and Turbo Mufflers.