Engine vacuum and timing for cammed 400
I have read up on the topic of engine vacuum and idle speed on several Pontiac forums and have a few questions regarding timing and engine vacuum on a 67 400 with an aftermarket cam:
Comp Cams 51-224-4 Extreme Energy
- Hydraulic Flat Tappet
- 1,800-6,000 rpm range
- 230/236 duration @ .050" lift (274/286 advertised)
- 0.488 intake/0.491 exhaust
- LSA 110*
Lars Tuning secrets sticky states that on "a performance engine, I like to see initial timing in the 16 – 18 degree range. Mild-cammed engines can get by with a little less. Big cammed engines like 20 to 24 degrees initial. But set total to 36 as a starting point."
My questions: Would my cam be considered mild or big? How much engine vacuum at idle (auto in park) should I expect to see? Idle speed is around 950 rpm in order to keep it running.
Holley 750 DP, no choke, heat crossover in intake is blocked, phenolic 1" open spacer to keep the fuel from boiling, Edelbrock intake with water crossover separated
I ask because my engine seems to like about 12* initial according to the timing light (vac adv unplugged and capped). Any more and I have trouble getting it to start, especially if the engine is warm. I'm sure if either my balancer slipped or the cam timing were slightly off I could better explain the quirky nature of this thing. I'm not sure how to check the balancer but will check the cam when I replace the timing cover (broken stud for water pump). Per Lars' article I will be pulling the HEI distributor to fix the shaft end play as soon as I can find a shim kit. I recall it felt like it need it the last time it was out. I want to get the little things worked out of the ignition system, idle, and fueling so I can get busy enjoying the drive while restoring it.
Any thoughts would be appreciated.