At what rpm , how far open are the primaries ? Lots of variables to be considered ..
750-800 rpm, transition slot showing square or about .020. Timing at 14 initial at idle. A few degrees either way makes little difference to the vacuum level. 4 corner idle screws tuned to best vacuum. 14" vac is the best I can get at any carb or timing setting. I know that is not too low. My 383 runs 7-8" vac, but it has a way bigger cam in it. Just curious.At what rpm , how far open are the primaries ? Lots of variables to be considered ..
Timing Events: intake open -1, close 36, exhaust open 48, close -4.I can say this. My cam has close to the same adv duration & 15+° more at .050 than yours . At 900 rpm mine has 13" of vacuum . I'll take a WAG that its related to valve timing , early opening. Late closing ??
Having the ring seal you have would make me very happy !!
I degreed the cam in at 107.5 to the recommended 108 intake centerline. So within a half degree. Close enough.I agree with 2old, Cam timing, factory cams are ground to run at machined timing specs, controlled only by mechanical setting off a pin at TDC. Aftermarket cams need to be dialed in to the spec for that cam, or you can throw the pin in and run with it. Because of higher lift and different LSA, a few degrees of timing shift in relation to crank position can make several inches of vacuum difference.
If you believe the intake is leaking in the valley, pull out your PCV, and spray flammable brake clean in the vent hole on each valve cover, while idling. A pick up off rpm would indicate a leak.
The 4 corner idle also bleeds more are than a standard 4bbL.
Thanks Bogie. That makes me feel better about the vacuum level.For the duration this sounds about where it should be. Even if you’re using no overlap, the vacuum is still sensitive to when the intake valve is closed in crank degrees. I this case the cam is starting to get into that late to close zone that will show a a small but steady vacuum drop.
14 inches of vacuum at an idle isn’t bad at all. Run the engine and don’t worry about it.I have about 500 miles on my new rebuilt 355 SBC. It has 10:1 CR. Compression test shows 175 PSI in all cylinders and 1-2% leakdown on all cylinders. The cam is a HR Straub. .050 duration is 215/224, advertised is 284/296, Lift is .470/.490. Centerlines 108/116, LSA is 112, Zero overlap. I am getting a steady 14" vacuum at idle. I kind of expected more vacuum at idle. I don't have power vacuum assist brakes, so it really doesn't hurt a thing. I just expected it to be higher. Just wondering if I may have leak. I can detect no external leaks, so if anything is leaking it would have to be at the bottom of the intake gaskets.
What vacuum would you guys expect from this setup?